Browsing by Author "Sfecci, Andrea"

Now showing 1 - 7 of 7
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    Non-well-ordered lower and upper solutions for semilinear systems of PDEs
    (SISSA, 2020-05) Fonda, Alessandro; Klun, Giuliano; Sfecci, Andrea
    We prove existence results for systems of boundary value problems involving elliptic second order differential operators. The as-sumptions involve lower and upper solutions, which may be either well-ordered, or not at all. The results are stated in an abstract framework, and can be translated also for systems of parabolic type.
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    On Dini derivatives of real functions
    (2021) Fonda, Alessandro; Klun, Giuliano; Sfecci, Andrea; mathematics
    For a continuous function f, the set Vf made of those points where the lower left derivative is strictly less than the upper right derivative is totally disconnected. Besides continuity, alternative assumptions are proposed so to preserve this property. On the other hand, we construct a function f whose set Vf coincides with the entire domain, and nevertheless f is continuous on an infinite set, possibly having infinitely many cluster points. Some open problems are proposed.
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    On the Dirichlet problem associated to bounded perturbations of positively-(p, q)-homogeneous Hamiltonian systems
    (2022-02-21) Fonda, Alessandro; Klun, Giuliano; Obersnel, Franco; Sfecci, Andrea; mathematics
    The existence of solutions for the Dirichlet problem associated to bounded perturbations of positively-(p, q)-homogeneous Hamiltonian sys tems is considered both in nonresonant and resonant situations. In order to deal with the resonant case, the existence of a couple of lower and up per solutions is assumed. Both the well-ordered and the non-well-ordered cases are analysed. The proof is based on phase-plane analysis and topo logical degree theory
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    Periodic bouncing solutions for nonlinear impact oscillators
    (SISSA, 2012-04) Fonda, Alessandro; Sfecci, Andrea; Mathematics; Functional Analysis and Applications
    We prove the existence of a periodic solution to a nonlinear impact oscillator, whose restoring force has an asymptotically linear behavior. To this aim, after regularizing the problem, we use phase-plane analysis, and apply the Poincare'–Bohl fixed point Theorem to the associated Poincare' map, so to find a periodic solution of the regularized problem. Passing to the limit, we eventually find the “bouncing solution” we are looking for.
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    Periodic solutions of nearly integrable Hamiltonian systems bifurcating from infinite-dimensional tori
    (2019-09-12) Fonda, Alessandro; Klun, Giuliano; Sfecci, Andrea
    We prove the existence of periodic solutions of some infinite-dimensional nearly integrable Hamiltonian systems, bifurcating from infinite-dimensional tori, by the use of a generalization of the Poincaré–Birkhoff Theorem.
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    Periodic solutions of second order differential equations in Hilbert spaces
    (SISSA, 2020-05) Fonda, Alessandro; Klun, Giuliano; Sfecci, Andrea
    We prove the existence of periodic solutions of some infinite-dimensional systems by the use of the lower/upper solutions method. Both the well-ordered and non-well-ordered cases are treated, thus generalizing to systems some well established results for scalar equations.
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    Well-ordered and non-well-ordered lower and upper solutions for periodic planar systems
    (2021-01-08) Fonda, Alessandro; Klun, Giuliano; Sfecci, Andrea; mathematics
    The aim of this paper is to extend the theory of lower and upper solutions to the periodic problem associated with planar systems of differential equations. We generalize previously given definitions and we are able to treat both the well-ordered case and the non-well-ordered case. The proofs involve topological degree arguments, together with a detailed analysis of the solutions in the phase plane.