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In this paper we study a class of Hardy--Sobolev type systems defined in $\mathbb{R}^N$ and coupled by a singular critical Hardy--Sobolev term. The main novelty of this work is that the orders of the singularities are independent and contained in a wide range. By means of variational techniques, we will prove the existence of positive bound and ground states for such a system. In particular, we find solutions as minimizers or Mountain--Pass critical points of the energy functional on the underlying Nehari manifold., Comment: arXiv admin note: text overlap with arXiv:2211.17047

In this paper, we prove a couple of new nonlinear functional inequalities of Sobolev type akin to the logarithmic Sobolev inequality. In particular, one of the inequalities reads $$ \int_{\mathbb{S}^1}\arctan\left(\frac{\partial_x u}{u}\right)\partial_xu \,dx\geq \arctan\left(\|u(t)\|_{\dot{W}^{1,1}(\mathbb{S}^1)}\right)\|u(t)\|_{\dot{W}^{1,1}(\mathbb{S}^1)}. $$ Then, these inequalities are used in the study of the nonlinear \emph{arctan}-fast diffusion equation $$ \partial_t u-\partial_x\arctan\left(\frac{\partial_x u}{u}\right)=0. $$ For this highly nonlinear PDE we establish a number of well-posedness results and qualitative properties.

In this work we analyze a class of nonlinear fractional elliptic systems involving Hardy--type potentials and coupled by critical Hardy-Sobolev--type nonlinearities in $\mathbb{R}^N$. Due to the lack of compactness at the critical exponent the variational approach requires a careful analysis of the Palais-Smale sequences. In order to overcome this loss of compactness, by means of a concentration--compactness argument the compactness of PS sequences is derived. This, combined with a energy characterization of the semi-trivial solutions, allow us to conclude the existence of positive ground and bound state solutions en terms of coupling parameter $\nu>0$ and the involved exponents $\alpha,\beta$., Comment: arXiv admin note: text overlap with arXiv:2211.17047

In this paper, by variational and topological arguments based on linking and $\nabla$-theorems, we prove the existence of multiple solutions for the following nonlocal problem with mixed Dirichlet-Neumann boundary data, $$ \left\{ \begin{array}{lcl} (-\Delta)^su=\lambda u+f(x,u) & &\text{in } \Omega, \\[2pt] \mkern+39mu u=0& &\text{on } \Sigma_{\mathcal{D}}, \\[2pt] \mkern+26mu \displaystyle \frac{\partial u}{\partial \nu}=0& &\text{on } \Sigma_{\mathcal{N}}, \end{array} \right. $$ where $(-\Delta)^s$, $s\in (1/2,1)$, is the spectral fractional Laplacian operator, $\Omega\subset\mathbb{R}^N$, $N>2s$, is a smooth bounded domain, $\lambda>0$ is a real parameter, $\nu$ is the outward normal to $\partial\Omega$, $\Sigma_{\mathcal{D}}$, $\Sigma_{\mathcal{N}}$ are smooth $(N-1)$-dimensional submanifolds of $\partial\Omega$ such that $\Sigma_{\mathcal{D}}\cup\Sigma_{\mathcal{N}}=\partial\Omega$, $\Sigma_{\mathcal{D}}\cap\Sigma_{\mathcal{N}}=\emptyset$ and $\Sigma_{\mathcal{D}}\cap\overline{\Sigma}_{\mathcal{N}}=\Gamma$ is a smooth $(N-2)$-dimensional submanifold of $\partial\Omega$.

In this work we analyze the behavior of truncated functionals as \begin{equation*} \int_{\mathbb{R}^N}\int_{B(x,\delta)} G\left(\frac{|u(x)-u(y)|}{|x-y|^{s}}\right)\frac{dydx}{|x-y|^N}\qquad\text{for }\delta\to0^+. \end{equation*} Here the function $G$ is an Orlicz function that in addition is assumed to be a regularly varying function at $0$. A prototype of such function is given by $G(t)=t^p(1+|\log(t)|)$ with $p\geq2$. These kind of functionals arise naturally in {\it peridynamics}, where long-range interactions are neglected and only those exerted at distance smaller than $\delta>0$ are taken into account, i.e., the {\it horizon} $\delta>0$ represents the range of interactions or nonlocality.\\ This work is inspired by the celebrated result by Bourgain, Brezis and Mironescu, who analyzed the limit $s\to1^-$ with $G(t)=t^p$. In particular, we prove that, under appropriate conditions, \begin{equation*} \lim\limits_{\delta\to0^+}\frac{p(1-s)}{G(\delta^{1-s})}\int_{\mathbb{R}^N}\int_{B(x,\delta)}G\left(\frac{|u(x)-u(y)|}{|x-y|^{s}}\right)\frac{dydx}{|x-y|^N}=K_{N,p}\int_{\mathbb{R}^N}|\nabla u(x)|^p dx, \end{equation*} for $p=index(G)$ and an explicit constant $K_{N,p}>0$. Moreover, the converse is also true, if the above localization limit exist as $\delta\to0^+$, the Orlicz function $G$ is a regularly varying function with $index(G)=p$.

This paper is focused on the solvability of a family of nonlinear elliptic systems defined in $\mathbb{R}^N$. Such equations contain Hardy potentials and Hardy-Sobolev criticalities coupled by a possible critical Hardy-Sobolev term. That problem arises as a generalization of Gross-Pitaevskii and Bose-Einstein type systems. By means of variational techniques, we shall find ground and bound states in terms of the coupling parameter $\nu$ and the order of the different parameters and exponents. In particular, for a wide range of parameters we find solutions as minimizers or Mountain-Pass critical points of the energy functional on the underlying Nehari manifold., Comment: 26 pages. arXiv admin note: text overlap with arXiv:2107.03737

Using the TNG50 cosmological simulation and observations from the Kilo-Degree Survey (KiDS), we investigate the connection between galaxy mergers and optical morphology in the local Universe over a wide range of galaxy stellar masses ($8.5\leqslant\log(M_\ast/\text{M}_\odot)\leqslant11$). To this end, we have generated over 16,000 synthetic images of TNG50 galaxies designed to match KiDS observations, including the effects of dust attenuation and scattering, and used the $\mathrm{\mathtt{statmorph}}$ code to measure various image-based morphological diagnostics in the $r$-band for both data sets. Such measurements include the Gini-$M_{20}$ and concentration-asymmetry-smoothness statistics. Overall, we find good agreement between the optical morphologies of TNG50 and KiDS galaxies, although the former are slightly more concentrated and asymmetric than their observational counterparts. Afterwards, we trained a random forest classifier to identify merging galaxies in the simulation (including major and minor mergers) using the morphological diagnostics as the model features, along with merger statistics from the merger trees as the ground truth. We find that the asymmetry statistic exhibits the highest feature importance of all the morphological parameters considered. Thus, the performance of our algorithm is comparable to that of the more traditional method of selecting highly asymmetric galaxies. Finally, using our trained model, we estimate the galaxy merger fraction in both our synthetic and observational galaxy samples, finding in both cases that the galaxy merger fraction increases steadily as a function of stellar mass., Comment: 18 pages, 12 figures. Accepted for publication in MNRAS

In this work we study the existence of solutions to the following critical fractional problem with concave-convex nonlinearities, \begin{equation*} \left \{ \begin{array}{l} (-\Delta)^su=\lambda u^q+u^{2_s^*-1},\ u>0\quad\text{in }\Omega,\\[3pt] \mkern+51mu u=0\quad\text{on } \Sigma_{\mathcal{D}}\\ \mkern+36mu \displaystyle \frac{\partial u}{\partial \nu}=0\quad\text{on } \Sigma_{\mathcal{N}} \end{array} \right. \end{equation*} where $\Omega\subset\mathbb{R}^N$ is a smooth bounded domain, $\frac{1}{2}0$, $\nu$ is the outwards normal to $\partial\Omega$, $\Sigma_{\mathcal{D}}$, $\Sigma_{\mathcal{N}}$ are smooth $(N-1)$-dimensional submanifolds of $\partial\Omega$ such that $\Sigma_{\mathcal{D}}\cup\Sigma_{\mathcal{N}}=\partial\Omega$, $\Sigma_{\mathcal{D}}\cap\Sigma_{\mathcal{N}}=\emptyset$, and $\Sigma_{\mathcal{D}}\cap\overline{\Sigma}_{\mathcal{N}}=\Gamma$ is a smooth $(N-2)$-dimensional submanifold of $\partial\Omega$.\newline In particular, we will prove that, for the sublinear case $00$. We will also prove that solutions are bounded.

In this work we study the following class of systems of coupled nonlinear fractional nonlinear Schr\"odinger equations, \begin{equation*} \left \{ \begin{array}{l} (-\Delta)^s u_1+ \lambda_1 u_1= \mu_1 |u_1|^{2p-2}u_1+\beta |u_2|^{p} |u_1|^{p-2}u_1 \quad\text{in }\mathbb{R}^N,\\[3pt] (-\Delta)^s u_2 + \lambda_2 u_2= \mu_2 |u_2|^{2p-2}u_2+\beta |u_1|^{p}|u_2|^{p-2}u_2 \quad\text{in }\mathbb{R}^N, \end{array} \right. \end{equation*} where $ u_1,\, u_2\in W^{s,2}(\mathbb{R}^N)$, with $ N=1,\, 2,\, 3$; $\lambda_j,\,\mu_j>0$, $j=1,2$, $\beta\in \mathbb{R}$, $p\geq 2$ and $\displaystyle\frac{p-1}{2p}N0$ for $j=1,\ldots ,m\ge 3$, the coupling parameters $\beta_{jk}=\beta_{kj}\in \mathbb{R}$ for $j,k=1,\ldots,m$, $j\neq k$. For this system we prove similar results as for $m=2$, depending on the values of the parameters $\beta_{jk}, p, \lambda_j,\mu_j$, (for $j,k=1,\ldots,m$, $j\neq k$).

We consider the existence of bound and ground states for a family of nonlinear elliptic systems in $\mathbb{R}^N$, which involves equations with critical power nonlinearities and Hardy-type singular potentials. The equations are coupled by what we call ``Schr\"odinger-Korteweg-de Vries'' non-symmetric terms, which arise in some phenomena of fluid mechanics. By means of variational methods, ground states are derived for several ranges of the positive coupling parameter $\nu$. Moreover, by using min-max arguments, we seek bound states under some energy assumptions., Comment: 26 pages, 3 figures. arXiv admin note: text overlap with arXiv:2107.03737

We study the existence of bound and ground states for a class of nonlinear elliptic systems in $\mathbb{R}^N$. These equations involve critical power nonlinearities and Hardy-type singular potentials, coupled by a term containing up to critical powers. More precisely, we find ground states either the positive coupling parameter $\nu$ is large or $\nu$ is small under suitable assumptions on the other parameters of the problem. Furthermore, bound states are found as Mountain-Pass-type critical points of the underlying functional constrained on the Nehari manifold. Our variational approach improves some known results and allows us to cover range of parameters which have not been considered previously., Comment: 30 pages

In this work we prove a strong maximum principle for fractional elliptic problems with mixed Dirichlet-Neumann boundary data which extends the one proved by J. D\'avila to the fractional setting. In particular, we present a comparison result for two solutions of the fractional Laplace equation involving the spectral fractional Laplacian endowed with homogeneous mixed boundary condition. This result represents a non-local counterpart to a Hopf's Lemma for fractional elliptic problems with mixed boundary data., Comment: 13 pages, This paper is published in Fract. Calc. Appl. Anal., Vol. 24, No 6 (2021), pp. 1699 1715, so cite it with the journal coordinates

We develop three asymptotic models of surface waves in a non-newtonian fluid with odd viscosity. This viscosity is also known as Hall viscosity and appears in a number of applications such as quantum Hall fluids or chiral active fluids. Besides the odd viscosity effects, these models capture both gravity and capillary forces up to quadratic interactions and take the form of nonlinear and nonlocal wave equations. Two of these models describe bidirectional waves while the third PDE studies the case of unidirectional propagation. We also prove the well-posedness of these asymptotic models in spaces of analytic functions and in Sobolev spaces. Finally, we present a number of numerical simulations for the unidirectional model., Comment: 3 figures

In this work we prove the non-degeneracy of the critical points of the Robin function for the Fractional Laplacian under symmetry and convexity assumptions on the domain $\Omega$. This work extends to the fractional setting the results of M. Grossi concerning the classical Laplace operator.

In this work we analyze the behavior of the spectrum of the peridynamic fractional $p$-Laplacian, $(-\Delta_p)_{\delta}^s$, under the limit process $\delta\to0^+$ or $\delta\to+\infty$. We prove spectral convergence to the classical $p$-Laplacian under a suitable scaling as $\delta\to0^+$ and to the fractional $p$-Laplacian as $\delta\to+\infty$.

In this work we introduce volume constraint problems involving the nonlocal operator $(-\Delta)_{\delta}^{s}$, closely related to the fractional Laplacian $(-\Delta)^{s}$, and depending upon a parameter $\delta>0$ called horizon. We study the associated linear and spectral problems and the behavior of these volume constraint problems when $\delta\to0^+$ and $\delta\to+\infty$. Through these limit processes on $(-\Delta)_{\delta}^{s}$ we derive spectral convergence to the local Laplacian and to the fractional Laplacian as $\delta\to 0^+$ and $\delta \to +\infty$ respectively, as well as we prove the convergence of solutions of these problems to solutions of a local Dirichlet problem involving $(-\Delta)$ as $\delta\to0^+$ or to solutions of a nonlocal fractional Dirichlet problem involving $(-\Delta)^s$ as $\delta\to+\infty$., Comment: 24 pages

This paper is devoted to the study of the existence of positive solutions for a problem related to a higher order fractional differential equation involving a nonlinear term depending on a fractional differential operator, $$(-\Delta)^{\alpha} u=\lambda u+ (-\Delta)^{\beta}|u|^{p-1}u \quad \mbox{in}\quad \Omega;\qquad (-\Delta)^{j}u=0\quad \mbox{on}\quad \partial\Omega,\quad \mbox{for}\quad j\in\mathbb{Z},\: 0\leq j< [\alpha]$$ where $\Omega$ is a bounded domain in $\mathbb{R}^{N}$, $0<\beta<1$, $\beta<\alpha<\beta+1$ and $\lambda>0$. In particular, we study the fractional elliptic problem, $$ (-\Delta)^{\alpha-\beta} u= \lambda(-\Delta)^{-\beta}u+ |u|^{p-1}u \quad\mbox{in} \quad \Omega;\qquad u=0 \quad \hbox{on} \quad \partial\Omega,$$ and we prove existence or nonexistence of positive solutions depending on the parameter $\lambda>0$, up to the critical value of the exponent $p$, i.e., for $1

In this work we study the solvability of the Cauchy Problem for a quasilinear degenerate high-order parabolic equation \begin{equation*} \left\{ \begin{tabular}{lcl} $u_t=(-1)^{m-1}\nabla\cdot(f^n(|u|)\nabla\Delta^{m-1}u)$ & &in $\mathbb{R}^N\times\mathbb{R}_+$, $u(x,0)=u_0(x)$& & in $\mathbb{R}^N$, \end{tabular} \right. \end{equation*} with $m\in\mathbb{N},\ m>1$ and $n>0$ a fixed exponent. Moreover, $f$ is a continuous monotone increasing positive bounded function with $f(0)=0$ and the initial data $u_0(x)$ is bounded smooth and compactly supported. Thus, through an homotopy argument based on an analytic $\varepsilon$-regularization of the degenerate term $f^n(|u|)$ we are able to extract information about the solutions inherited from the polyharmonic equation when $n=0$.

This paper is devoted to the existence of positive solutions for a problem related to a fourth-order differential equation involving a nonlinear term depending on a second order differential operator, $$(-\Delta)^2 u=\lambda u+ (-\Delta)|u|^{p-1}u,$$ in a bounded domain $\Omega\subset\mathbb{R}^N$, $N\geq 7$, and assuming homogeneous Navier boundary conditions. In particular, we study a second order equation involving a nonlocal term of the form, $$-\Delta u=\lambda (-\Delta)^{-1} u+|u|^{p-1}u,$$ under Dirichlet boundary conditions and we prove the existence of positive solutions depending on the positive real parameter $\lambda>0$, up to the critical value of the exponent $p$, i.e., when $1

In this work we study the existence of solutions to the critical Brezis-Nirenberg problem when one deals with the spectral fractional Laplace operator and mixed Dirichlet-Neumann boundary conditions, i.e., $$ \left\{\begin{array}{rcl} (-\Delta)^su & = & \lambda u+u^{2_s^*-1},\quad u>0\quad\mbox{in}\quad \Omega,\\ u & = & 0\quad\mbox{on}\quad \Sigma_{\mathcal{D}},\\ \displaystyle\frac{\partial u}{\partial \nu} & = & 0\quad\mbox{on}\quad \Sigma_{\mathcal{N}}, \end{array}\right. $$ where $\Omega\subset\mathbb{R}^N$ is a regular bounded domain, $\frac{1}{2}