Special Session 105: Nonlinear Differential Problems on Flat and Curved Structures: Variational and Topological Methods

Nonlinear differential equations in the whole space

Eleonora Amoroso
University of Messina
Italy
Co-Author(s):    
Abstract:
In this talk, we present some existence and multiplicity results for nonlinear elliptic equations involving the p-Laplacian operator and which are defined in the whole space. As a special case, the existence of two non-zero solutions, one with negative energy and other with positive one, for equations having combined effects of concave and convex nonlinearities is obtained. The approach is based on variational methods and critical point theory. This is a joint work with G. Bonanno and K. Perera.

Multiple Solutions for Nonlinear Elliptic Differential Inclusions

Gabriele Bonanno
University of Messina
Italy
Co-Author(s):    
Abstract:
A multiplicity result for elliptic differential inclusions is presented. The approach is based on variational methods and a theorem on the existence of two generalized nonzero critical points is applied. Finally, differential equations with discontinuous nonlinearities are studied.

A Variant Prescribed Curvature Flow on Closed Surfaces with Negative Euler Characteristic

Franziska Borer
Technical University of Berlin
Germany
Co-Author(s):    Peter Elbau, Tobias Weth
Abstract:
Let $(M,\bar g)$ be a two-dimensional, smooth, closed, connected, oriented Riemann manifold endowed with a smooth background metric $\bar g$. A classical problem raised by Kazdan and Warner is the question which smooth functions $f:M\to\mathbb{R}$ arise as the Gauss curvature $K_g$ of a conformal metric $g(x)=\mathrm{e}^{2u(x)}\bar g(x)$ on $M$ and to characterise the set of all such metrics. In this talk, we give an overview on several results concerning prescribed Gauss curvature problems depending on the given function $f$ as well as the Euler characteristic $\chi(M)$ of the manifold $M$, and consider everything in the flow context. Finally we will see, that in the case where the characteristic $\chi(M)$ is negative and $f$ is sign-changing, we have to introduce a new kind of prescribed Gauss curvature flow to solve the problem. This is a joint work with Peter Elbau and Tobias Weth.

Two positive solutions for parametric singular $p$-Laplacian type problems

Pasquale Candito
Mediterranean University of Reggio Calabria
Italy
Co-Author(s):    
Abstract:
The aim of this talk is to discuss some recent results about the existence of at least two positive solutions for parametric singular $p$-Laplacian type problems.

Existence and regularity results for a class of singular parabolic problems with L1 data

Ida de Bonis
Sapienza University of Rome
Italy
Co-Author(s):    Maria Michaela Porzio
Abstract:
In this paper we prove existence and regularity results for a class of parabolic problems with irregular initial data and lower order terms singular with respect to the solution. We prove that, even if the initial datum is not bounded but only in $L^1(\Omega)$, there exists a solution that `instantly` becomes bounded.

Tumor-inmune cell interactions by a chemotaxis system with logistic source

Rafael Diaz Fuentes
University of Cagliari
Italy
Co-Author(s):    
Abstract:
This talk presents an extension of a previously studied class of chemotaxis systems, in which a source term of logistic type is introduced into one of the three parabolic partial differential equations. The source term of logistic type is given by the expression $u^k(1-u)$. This choice generalizes some models previously described in literature. We study some properties of the classical solutions for the superquadratic and quadratic degradation rate, i.e., $k>1$ and $k=1$ respectively. Under suitable assumptions on the initial data and the coefficients of the system, the global-in-time existence of the classical solutions and their uniform boundedness are proved in bounded domains of $\mathbb{R}^n$, $n \geq 3$.

Existence results for nonlinear differential problems and applications to neural networks

Giuseppina D`Agui
University of Messina
Italy
Co-Author(s):    
Abstract:
This talk concerns results on the existence of positive solutions to boundary value problems for ordinary differential equations. In particular, we show the existence of a periodic weak solution to a nonlinear parametric differential problem using variational methods. The core approach is based on critical point theorems, with particular emphasis on a recently developed non-zero local minimum theorem. The results presented are part of the research carried out within the project: PNRR-MAD-2022-12376692- PNRR-Missione 6 - Componente 2 Investimento 2.1 Valorizzazione e Potenziamento della Ricerca Biomedica del SSN

Tumbling Downhill along a Given Curve

Jean-Pierre Eckmann
University of Geneva
Switzerland
Co-Author(s):    Y. Sobolev and T. Tlusty
Abstract:
A cylinder will roll down an inclined plane in a straight line. A cone will wiggle along a circle on that plane and then will stop rolling. We ask the inverse question: For which curves drawn on the inclined plane $R^2$ can one chisel a shape that will roll downhill following precisely this prescribed curve and its translationally repeated copies? This is a nice, and easy to understand problem, but the solution is quite interesting. (After a Nature paper, Solid-body trajectoids shaped to roll along desired pathways, August 2023, and Notices AMS, Vol 71, 2024)

Ordered solutions for degenerate Kirchhoff problems

Francesca Faraci
University of Catania
Italy
Co-Author(s):    K.Silva
Abstract:
In this talk we study a parametrized Kirchhoff type equation with two degeneracy points. The existence of two $H_0^1(\Omega)$-norm ordered solutions is established for small value of the parameter via a careful analysis of the fiber maps associated to the energy functional. As a consequence we show existence of multiple or even infinitely many solutions to degenerate Kirchhoff equations. Some applications are given. Based on the paper: F. Faraci, K. Silva, Ordered solutions for degenerate Kirchhoff problems, submitted.

Singular (N,q)-Lapacian equation on Riemannian manifolds.

Csaba Farkas
Sapientia Hungarian University of Transylvania
Romania
Co-Author(s):    
Abstract:
n this talk, we aim to investigate the existence of solutions for a singular elliptic equation of (N,q)-Laplacian type on a non-compact, complete N-dimensional Riemannian manifold with nonnegative Ricci curvature and Euclidean volume growth. The nonlinearity appearing in the problem exhibits exponential critical growth in the Moser-Trudinger sense. By combining variational arguments with a Lions-type compactness principle, we guarantee the existence of a non-zero, isometry-invariant solution for such problems.

Riccati pairs: an alternative approach to Hardy inequalities

Sandor Kajanto
Babes-Bolyai University, Cluj-Napoca
Romania
Co-Author(s):    
Abstract:
Riccati pairs allow us to establish Hardy inequalities on Riemannian manifolds by solving corresponding Riccati-type ordinary differential inequalities. This method relies solely on simple convexity arguments, the divergence theorem, and the Laplace comparison theorem. Moreover, it is symmetrization-free, making it broadly applicable: inequalities formulated on model space forms extend naturally to general manifolds with lower sectional curvature.

Sharp Sobolev inequalities on noncompact Riemannian manifolds

Alexandru Kristaly
Babes-Bolyai University
Romania
Co-Author(s):    
Abstract:
In their seminal work, Cordero-Erausquin, Nazaret and Villani [Adv. Math., 2004] proved sharp Sobolev inequalities in Euclidean spaces via Optimal Transport, raising the question whether their approach is powerful enough to produce sharp Sobolev inequalities also on Riemannian manifolds. By using $L^1$-optimal transport approach, the compact case has been successfully treated by Cavalletti and Mondino [Geom. Topol., 2017], even on metric measure spaces verifying the synthetic lower Ricci curvature bound. In the present talk we affirmatively answer the above question for noncompact Riemannian manifolds with non-negative Ricci curvature; namely, by using Optimal Transport theory with quadratic distance cost, sharp $L^p$-Sobolev and $L^p$-logarithmic Sobolev inequalities (both for $p>1$ and $p=1$) are established, where the sharp constants contain the asymptotic volume ratio arising from precise asymptotic properties of the Talentian and Gaussian bubbles, respectively. Talk based on [A]. [A] Krist\`aly Alexandru, Sharp Sobolev inequalities on noncompact Riemannian manifolds with $Ric\geq 0$ via optimal transport theory. Calc. Var. Partial Differential Equations 63 (2024), no. 8, Paper No. 200.

On some properties of solutions to a class of parabolic system

Monica Marras
University of Cagliari
Italy
Co-Author(s):    Y. Chiyo, T. Yokota, S. Vernier-Piro
Abstract:
We are interested in qualitative properties as blow-up phenomena, decay in time, boundedness, global existence for solutions of some classes of parabolic systems. In particular, we study a new class of Keller Segel models, which presents a limited flux and an optimal transport of cells density according to chemical signal density.

Sharp Morrey-Sobolev inequalities on Finsler manifolds with nonnegative Ricci curvature

Agnes Mester
University of Bern
Switzerland
Co-Author(s):    Alexandru Kristaly, Ildiko I. Mezei
Abstract:
We present sharp Morrey-Sobolev inequalities (i.e., in the case $p>n$) on $n$-dimensional Finsler manifolds having nonnegative $n$-Ricci curvature. For this purpose, we elaborate suitable anisotropic symmetrization arguments by applying the sharp isoperimetric inequality available on these spaces. We also provide a Hardy-type inequality within the same geometric setting. As application, by using variational arguments, we guarantee the existence & multiplicity of solutions for certain elliptic PDEs involving the Finsler-Laplace operator. Our results are also new in the Riemannian setting. Talk based on Kristaly A, Mester A, Mezei I. I, Sharp Morrey-Sobolev inequalities and eigenvalue problems on Riemannian- Finsler manifolds with nonnegative Ricci curvature, Commun. Contemp. Math, 25 (2023), no. 10, Paper No. 2250063.

Nonsmooth analysis for boundary value problems with discontinuous nonlinearities

Valeria Morabito
University of Messina
Italy
Co-Author(s):    
Abstract:
In this talk, we investigate the existence of solutions for boundary value problems governed by nonlinear differential equations with discontinuous nonlinearities, employing nonsmooth techniques from variational analysis. Specifically, we focus on Clarke`s theory for locally Lipschitz functionals, which provides a framework for analyzing functionals that exhibit nonsmooth behavior, extending classical variational methods to non-smooth setting.

Sharp inequalities on Riemannian manifolds with Euclidean volume growth

Carlo Morpurgo
University of Missouri
USA
Co-Author(s):    Luigi Fontana, Liuyu Qin
Abstract:
In this talk, I will discuss recent results on Moser-Trudinger inequalities on complete Riemannian manifolds with nonnegative Ricci curvature and large volume growth. These inequalities will feature different best constants under different norm conditions. The main tools involved in the proof are sharp asymptotic and global estimates for heat kernels and Green functions, combined with recent results on Adams inequalities on metric measure spaces, obtained in joint work with Liuyu Qin.

A study of the Kuramoto model for synchronization phenomena based on a degenerate partial differential equation

Sergio Polidoro
Dipartimento FIM - Universit\`{a} di Modena e Reggio Emilia
Italy
Co-Author(s):    Giulio Pecorella, Cecilia Vernia
Abstract:
We consider a semilinear integro-differential equation that arises when introducing inertial effects in the Kuramoto model. Based on the known theory of degenerate Kolmogorov operators, existence, uniqueness and regularity results for the relevant Cauchy problem are discussed. Moreover, a stable numerical operator, which is consistent with the degenerate Kolmogorov operator, is provided in order to produce numerical solutions. Numerical experiments show how the synchronization phenomena depend on the parameters of the Kuramoto model with inertia.

A Cauchy problem and a semigroup of positive operators

AUGUSTA RATIU
LUCIAN BLAGA UNIVERSITY OF SIBIU
Romania
Co-Author(s):    Augusta Ratiu, Mihai Ilina
Abstract:
Let $j\in {\mathbb Z}$. Motivated by Swiderski's result [4], the following Cauchy problem $$ \left\{ \begin{array}{l} u_t^{\prime}=xu_{xx}^{\prime\prime}-(j-1)u_x^{\prime},\, x\geq 0,\, t>0, \nonumber \ \displaystyle\lim_{t\to 0^{+}}u(t,x)=f(x),\,\, x\geq 0, \nonumber\end{array}\right.$$ was considered in the paper [2]. A semigroup of positive operators was investigated in [3] and it was proved that it provides a solution of the Cauchy problem. Direct approaches to find solutions were also considered in [3]. The Cauchy problem $$ \left\{ \begin{array}{l} u_t^{\prime}=\dfrac{x}{2}u_{xx}^{\prime\prime},\, x\geq 0,\, t>0, \nonumber \ \displaystyle\lim_{t\to 0^{+}}u(t,x)=f(x),\,\, x\geq 0, \nonumber\end{array}\right.$$ was investigated in [1] using the theory of $C_0$-semigroups. We will present the connections between the solutions of the two problems. $$ $$ References $$ $$ [1] F. Altomare, I. Carbone, On Some Degenerate Differential Operators on Weighted Function Spaces, J. Math. Anal. Appl. 213 (1997), 308-333. $$ $$ [2] U. Abel, A.M. Acu, M. Heilmann, I. Ra\c sa, On some Cauchy problems and positive linear operators (manuscript) $$ $$ [3] U. Abel, A.M. Acu, M. Heilmann, I. Ra\c sa, Commutativity and spectral properties for a general class of Sz\`asz-Mirakjan-Durrmeyer operators, arXiv:2407.21722 $$ $$ [4] T. Swiderski, Global approximation theorems for the generalized modified Sz\`asz-Mirakyan operators in polynomial weight spaces, Demo. Math., 36(2), 2003, 383-392.

On multiplicative time-dependent perturbations of semigroups and cosine families generators

Valentina Taddei
Department of Sciences and Methods for Engineering, University of Modena and Reggio Emilia
Italy
Co-Author(s):    Erica Ipocoana
Abstract:
We investigate the vibrating string equation $\begin{equation*} \frac{\partial^2 u}{\partial t^2}= a(t) \frac{\partial^{2}u}{\partial \xi^{2}} + g\biggl(t,\xi,u, \frac{\partial u}{\partial t} \biggr), \quad t \in[0,b], \xi \in (0,1), \end{equation*}$ where the tension coefficient $a$ varies with time. Our strategy consists in transforming the PDE into the equivalent semilinear ODE $\begin{equation*} \ddot x(t)=a(t)A x(t) + f(t,x(t),\dot x(t)), \quad t \in [0,b], \end{equation*}$ in the Banach space $ L^p([0,1]), $ having, as linear part, a multiplicative time-dependent perturbation of the spatial second derivative operator $ A $, generating a cosine family. Our technique is based on the reduction to the associated first order problem, whose linear part consists into a multiplicative time-dependent perturbation of a semigroup generator. The aim of our talk is providing sufficient conditions guaranteeing that such perturbations respectively generates a fundamental and an evolution system, finding an explicit formula in both cases.

Nonlinear sampling Durrmeyer operators in functional spaces

Arianna Travaglini
University of Florence
Italy
Co-Author(s):    Gianluca Vinti
Abstract:
Among sampling type operators, the Generalized Durrmeyer-Sampling type series represents a generalization of both the Generalized and Kantorovich Sampling operators. The talk is focused on some recent approximation results for the Nonlinear version of Durrmeyer-Sampling type operators. \ For what concerns the space of continuous functions, a pointwise and uniform convergence theorem is provided. Moreover, approximation results for the nonlinear sampling Durrmeyer operators in the general setting of Orlicz spaces are also discussed. This results also ensures convergence in notable specific cases, such as in $L^p$-spaces, Zygmund spaces, and exponential spaces. Moreover, by considering the case of functions that are not necessarily continuous, these findings prove especially valuable in practical applications, where most real-world signals, such as digital images, are not mathematically represented by continuous functions.

Discrete and semi-discrete sampling type operators and applications to image segmentation

Gianluca Vinti
Department of Mathematics and Informatics, University of Perugia
Italy
Co-Author(s):    
Abstract:
In this talk, I will present some convergence results for discrete and semi-discrete operators of sampling type and I will show their applications to digital image processing. In particular, I will use a family of the above operators to solve a medical problem concerning the segmentation of the patent lumen of the aortic vessel. The above problem will be discussed showing two approaches: a deterministic one, that exploits results of approximation theory and one based on artificial intelligence methods through the use of convolutional neural networks. Finally, I will compare them each other by the numerical estimation of some similarity indexes.