Rendiconti dell’Istituto di Matematica dell’Università di Trieste: an International Journal of Mathematics vol.57 (2025)

This research project considers the d-dimensional MagnetoHydroDynamics (MHD) system defined on a sufficiently smooth bounded domain, d = 2, 3 with homogeneous boundary conditions, and subject to external sources assumed to cause instability. The initial conditions for both fluid and magnetic equations are taken of low regularity. We then seek to uniformly stabilize such MHD system in the vicinity of an unstable equilibrium pair, in the critical setting of correspondingly low regularity spaces, by means of explicitly constructed, static, feedback controls, which are localized on an arbitrarily small interior subdomain. In addition, the actuators will be minimal in number. The resulting space of well-posedness and stabilization is a suitable product space eB2−2/p q,p (Ω) × eB2−2/p q,p (Ω), 1 < p < 2q 2q−1 , q > d, of tight Besov spaces for the fluid velocity component and the magnetic field component (each “close” to L3(Ω) for d = 3). It is known that such Besov space does not recognize compatibility conditions at the boundary, yet it provides a “minimal” level of regularity necessary to handle the nonlinear terms. In this paper we provide a solution of the first step: uniform stabilization of the linearized MHD. Showing maximal Lp-regularity up to T = ∞ for the feedback stabilized linearized system is critical for the analysis of well-posedness and stabilization of the feedback nonlinear problem. The solution of the nonlinear stabilization problem is to be given in a successive paper [29].

We prove advanced regularity results for solutions to a sixth order equation arising in the mechanical Kirchhoff-Love’s type model of the static equilibrium of a nanoplate in bending. Such regularity properties play a crucial role in the treatment, among others, of the inverse problem consisting in the determination of the Winkler coefficient of a nanoplate.

We classify all closed non-orientable P2-irreducible 3- manifolds obtained by identifying the faces of a cube, i.e. those with cubic-complexity one. We show that they are the four flat ones.

Via the global bifurcation theorem due to Rabinowitz, the paper shows bifurcation properties of the solutions of the following nonlinear Dirichlet problem, involving a double phase operator, that is ( −Δap u − νΔmu = λa(x)|u|m−2u + f(x, u) in Ω, u = 0 on ∂Ω, where 1 < m < p < N, p/m < 1 + 1/N and λ, ν ∈ R.

We classify completely the equivalence groups and the classical Lie point symmetry groups of generalized radial Liouville-Bratu- Gelfand problems.