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Tommaso Leonori

Publications and source records attributed to Tommaso Leonori.

13 recordsLinked to original sources
arXiv2025

Quasilinear elliptic equations with singular quadratic growth terms

In this paper we deal with positive solutions for singular quasilinear problems whose model is $$ \begin{cases} -Δu + \frac{|\nabla u|^2}{(1-u)^γ}=g & \mbox{in $Ω$,}\newline \hfill u=0 \hfill & \mbox{on $\partialΩ$,} \end{cases} $$ where $Ω$ is a bounded open set of $\mathbb{R}^N$, $g\geq 0 $ is a function in some Lebesgue space, and $γ>0$. We prove both existence and nonexistence of solutions depending on the value of $γ$ and on the size of $g$.

math.AP↗
arXiv2025

Existence and nonexistence of solutions for singular quadratic quasilinear equations

We study both existence and nonexistence of nonnegative solutions for nonlinear elliptic problems with singular lower order terms that have natural growth with respect to the gradient, whose model is $$ \begin{cases} -Δu + \frac{|\nabla u|^2}{u^γ} = f & \mbox{in } Ω,\newline \hfill u=0 \hfill & \mbox{on } \partial Ω, \end{cases} $$ where $Ω$ is an open bounded subset of $\mathbb{R}^N $, $γ> 0$ and $f$ is a function which is strictly positive on every compactly contained subset of $Ω$. As a consequence of our main results, we prove that the condition $γ<2$ is necessary and sufficient for the existence of solutions in $H^{1}_{0}(Ω)$ for every sufficiently regular $f$ as above.

math.AP↗
arXiv2024

Gradient estimates for quasilinear elliptic Neumann problems with unbounded first-order terms

This paper studies global a priori gradient estimates for divergence-type equations patterned over the $p$-Laplacian with first-order terms having polynomial growth with respect to the gradient, under suitable integrability assumptions on the source term of the equation. The results apply to elliptic problems with unbounded data in Lebesgue spaces complemented with Neumann boundary conditions posed on convex domains of the Euclidean space.

math.AP↗
arXiv2024

On maximal regularity estimates for quasilinear evolution equations via the integral Bernstein method

This work addresses the problem of (global) maximal regularity for quasilinear evolution equations with sublinear gradient growth and right-hand side in Lebesgue spaces, complemented with Neumann boundary conditions. The proof relies on a suitable variation of the Bernstein technique and the Bochner identity, and provides new results even for the simpler parabolic $p$-Laplacian equation with unbounded source term. As a byproduct we also obtain a second-order estimate that can be of independent interest when the right-side of the equation belongs to $L^m$, $m\neq 2$. This approach leads to new results even for stationary problems.

math.AP↗
arXiv2023

The best approximation of a given function in $L^2$-norm by Lipschitz functions with gradient constraint

The starting point of this paper is the study of the asymptotic behavior, as $p\to\infty$, of the following minimization problem $$ \min\left\{\frac1{p}\int|\nabla v|^{p}+\frac12\int(v-f)^2 \,, \quad \ v\in W^{1,p} (Ω)\right\}. $$ We show that the limit problem provides the best approximation, in the $L^2$-norm, of the datum $f$ among all Lipschitz functions with Lipschitz constant less or equal than one. Moreover such approximation verifies a suitable PDE in the viscosity sense. After the analysis of the model problem above, we consider the asymptotic behavior of a related family of nonvariational equations and, finally, we also deal with some functionals involving the $(N-1)$-Hausdorff measure of the jump set of the function.

math.AP↗
arXiv2023

Global fractional Calderón-Zygmund type regularity

We obtain a global fractional Calderón-Zygmund regularity theory for the fractional Poisson problem. More precisely, for $Ω\subset \mathbb{R}^N$, $N \geq 2$, a bounded domain with boundary $\partial Ω$ of class $C^2$, $s \in (0,1)$ and $f \in L^m(Ω)$ for some $m \geq 1$, we consider the problem $$ \left. \begin{aligned} (-Δ)^s u = f \quad \mbox{in } Ω, \qquad\ u = 0 \quad \mbox{in } \mathbb{R}^N \setminus Ω, \end{aligned} \right. $$ and, according to $m$, we find the values of $s \leq t < \min\{1,2s\}$ and of $1 < p < +\infty$ such that $u \in L^{t,p}(\mathbb{R}^N)$ and such that $u \in W^{t,p}(\mathbb{R}^N)$.

math.AP↗
arXiv2022

Deterministic KPZ-type equations with nonlocal "gradient terms"

The main goal of this paper is to prove existence and non-existence results for deterministic Kardar-Parisi-Zhang type equations involving non-local "gradient terms". More precisely, let $Ω\subset \mathbb{R}^N$, $N \geq 2$, be a bounded domain with boundary $\partial Ω$ of class $C^2$. For $s \in (0,1)$, we consider problems of the form \[ \tag{KPZ} \left\{ \begin{aligned} (-Δ)^s u & = μ(x) |\mathbb{D}(u)|^q + λf(x), \quad && \mbox{ in } Ω,\\ u & = 0, && \mbox{ in } \mathbb{R}^N \setminus Ω, \end{aligned} \right. \] where $q > 1$ and $λ> 0$ are real parameters, $f$ belongs to a suitable Lebesgue space, $μ$ belongs to $L^{\infty}(Ω)$ and $\mathbb{D}$ represents a nonlocal "gradient term". Depending on the size of $λ> 0$, we derive existence and non-existence results. In particular, we solve several open problems posed in [4, Section 6] and [2, Section 7].

math.AP↗
arXiv2017

Comparison results for unbounded solutions for a parabolic Cauchy-Dirichlet problem with superlinear gradient growth

In this paper we deal with uniqueness of solutions to the following problem \[ \begin{cases} \begin{split} & u_t-Δ_p u=H(t,x,\nabla u) &\quad \text{in}\quad Q_T,\\ & u (t,x) =0 &\quad \text{on}\quad(0,T)\times \partial Ω,\\ & u(0,x)=u_0(x) &\quad \displaystyle\text{in }\quad Ω\end{split} \end{cases} \] where $Q_T=(0,T)\times Ω$ is the parabolic cylinder, $Ω$ is an open subset of $\mathbb{R}^N$, $N\ge2$, $1<p<N$, and the right hand side $\displaystyle H(t,x,ξ):(0,T)\timesΩ\times \mathbb{R}^N\to \mathbb{R}$ exhibits a superlinear growth with respect to the gradient term.

math.AP↗
arXiv2017

Principal Eigenvalue of Mixed Problem for the Fractional Laplacian: Moving the Boundary Conditions

We analyze the behavior of the eigenvalues of the following non local mixed problem $\left\{ \begin{array}{rcll} (-Δ)^{s} u &=& λ_1(D) \ u &\innΩ,\\ u&=&0&\inn D,\\ \mathcal{N}_{s}u&=&0&\inn N. \end{array}\right $ Our goal is to construct different sequences of problems by modifying the configuration of the sets $D$ and $N$, and to provide sufficient and necessary conditions on the size and the location of these sets in order to obtain sequences of eigenvalues that in the limit recover the eigenvalues of the Dirichlet or Neumann problem. We will see that the non locality plays a crucial role here, since the sets $D$ and $N$ can have infinite measure, a phenomenon that does not appear in the local case (see for example \cite{D,D2,CP}).

math.AP↗
arXiv2017

Parabolic equations with natural growth approximated by nonlocal equations

In this paper we study several aspects related with solutions of nonlocal problems whose prototype is $$ u_t =\displaystyle \int_{\mathbb{R}^N} J(x-y) \big( u(y,t) -u(x,t) \big) \mathcal G\big( u(y,t) -u(x,t) \big) dy \qquad \mbox{ in } \, Ω\times (0,T)\,, $$ being $ u (x,t)=0 \mbox{ in } (\mathbb{R}^N\setminus Ω)\times (0,T)\,$ and $ u(x,0)=u_0 (x) \mbox{ in } Ω$. We take, as the most important instance, $\mathcal G (s) \sim 1+ \fracμ{2} \frac{s}{1+μ^2 s^2 }$ with $μ\in \mathbb{R}$ as well as $u_0 \in L^1 (Ω)$, $J$ is a smooth symmetric function with compact support and $Ω$ is either a bounded smooth subset of $\mathbb{R}^N$, with nonlocal Dirichlet boundary condition, or $\mathbb{R}^N$ itself. The results deal with existence, uniqueness, comparison principle and asymptotic behavior. Moreover we prove that if the kernel rescales in a suitable way, the unique solution of the above problem converges to a solution of the deterministic Kardar-Parisi-Zhang equation.

math.AP↗
arXiv2014

Local estimates for parabolic equations with nonlinear gradient terms

In this paper we deal with local estimates for parabolic problems in $\mathbb{R}^N$ with absorbing first order terms, whose model is $\{ {l} u_t- Δu +u |\nabla u|^q = f(t,x) \quad &{in}\, (0,T) \times \mathbb{R}^N\,, \\[1.5 ex] u(0,x)= u_0 (x) &box{in}\, \mathbb{R}^N.$ where $T>0$, $N\geq 2$, $1<q\leq 2$, $f(t,x)\in L^1( 0,T; L^1_{\rm loc} (\mathbb{R}^N))$ and $u_0\in L^1_{\rm loc} (\mathbb{R}^N)$.

math.AP↗
arXiv2012

Ground states of self-gravitating elastic bodies

The existence of static, self-gravitating elastic bodies in the non-linear theory of elasticity is established. Equilibrium configurations of self-gravitating elastic bodies close to the reference configuration have been constructed in [6] using the implicit function theorem. In contrast, the steady states considered in this article correspond to deformations of the relaxed state with no size restriction and are obtained as minimizers of the energy functional of the elastic body.

math-ph↗