1,721,005 research outputs found
La biblioteca manoscritta greca di Achille Stazio
Full text linkLa presente ricerca mira alla ricostruzione della parte manoscritta greca della biblioteca appartenuta ad Achille Stazio (1524-1581), giunta alla chiesa di S. Maria e S. Gregorio in Vallicella per volontà testamentaria dell’illustre umanista portoghese e, perciò, nucleo fondativo dell’attuale Biblioteca Vallicelliana di Roma. Fonte primaria per l’individuazione dei codici vallicelliani provenienti dal lascito staziano è il reperimento delle postille marginali di mano del lusitano, il riconoscimento delle quali è possibile grazie a un’analisi paleografica fondata sul confronto con alcuni materiali sicuramente autografi. Il contenuto delle unità codicologiche individuate per mezzo dello spoglio sistematico del fondo manoscritto greco della Biblioteca Vallicelliana è quindi confrontato con le voci presenti negli antichi inventari relativi alla libraria di Stazio. I dati ricavati dall’analisi codicologica e paleografica dei manoscritti di provenienza staziana sono raccolti in schede descrittive e rielaborati alla luce delle informazioni desumibili dalla bibliografia, da materiale d’archivio e dalla comparazione con fondi librari analoghi. Le nuove acquisizioni emerse dallo studio dei codici consentono notevoli precisazioni sulla biblioteca e sui metodi di lavoro di Stazio, nonché di chiarire la storia di alcuni manoscritti vallicelliani e, più in generale, della Biblioteca Vallicelliana ai suoi primordi
Large KAM Tori for Quasi-linear Perturbations of KdV
No full textIn this paper we prove the persistence of space periodic multi-solitons of arbitrary size under any quasi-linear Hamiltonian perturbation, which is smooth and sufficiently small. This answers positively a longstanding question whether KAM techniques can be further developed to prove the existence of quasi-periodic solutions of arbitrary size of strongly nonlinear perturbations of integrable PDEs
Large amplitude traveling waves for the non-resistive MHD system
No full textWe prove the existence of large amplitude bi-periodic traveling waves (stationary in a moving frame) of the two-dimensional non-resistive Magnetohydrodynamics (MHD) system with a traveling wave external force with large velocity speed λ(ω_1, ω_2) and of amplitude of order O(λ^(1+) ) where λ ≫ 1 is a large parameter. For most values
of ω = (ω_1, ω_2) and for λ ≫ 1 large enough, we construct bi-periodic traveling wave solutions of arbitrarily large amplitude as λ → +∞. More precisely, we show that the velocity field is of order O(λ^(0+)), whereas the magnetic field is close to a constant vector as λ → +∞. Due to the presence of small divisors, the proof is based on a nonlinear Nash–Moser scheme adapted to construct nonlinear waves of large amplitude. The main difficulty is that the linearized equation at any approximate solution is an unbounded perturbation of large size of a diagonal operator and hence the problem is not perturbative. The invertibility of the linearized operator is then performed by using tools
from micro-local analysis and normal forms together with a sharp analysis of high- and low-frequency regimes with respect to the large parameter λ ≫ 1. To the best of our knowledge, this is the first result in which global in time, large amplitude solutions are constructed for the 2D non-resistive MHD system with periodic boundary conditions and also the first existence result of large amplitude quasi-periodic solutions for a nonlinear PDE in higher space dimension
Large KAM tori for perturbations of the defocusing NLS equation
No full textWe prove that small, semi-linear Hamiltonian perturbations of the defocusing nonlinear Schr\u7fodinger (dNLS) equation on the circle have an abundance of invariant tori of any size and (finite) dimension which support quasi-periodic solutions. When compared with previous results the novelty consists in considering perturbations which do not satisfy any symmetry condition (they may depend on x in an arbitrary way) and need not be analytic. The main diculty is posed by pairs of almost resonant dNLS frequencies. The proof is based on the integrability of the dNLS equation, in particular the fact that the nonlinear part of the Birkho coordinates is one smoothing. We implement a Newton-Nash-Moser
iteration scheme to construct the invariant tori. The key point is the reduction of linearized
operators, coming up in the iteration scheme, to 2 2 block diagonal ones with constant
coecients together with sharp asymptotic estimates of their eigenvalues
Quadratic Lifespan for the Sublinear -SQG Sharp Front Problem
No full textIn this paper we consider the generalized surface quasi-geostrophic α-SQG equations, in the
"sublinear regime" α ∈ (0, 1) and we study the stability of vortex patches close to vortex
disc
Roma religiosa. Monasteri e città (secc. IX–XVI)
No full textL’incontro di studi sul tema „Roma religiosa. Monasteri e città (secc. IX–XVI)” si è svolto a Roma il 27 e 28 novembre 2014, su iniziativa del Dipartimento di Storia, Culture, Religioni dell’Università degli studi di Roma „La Sapienza“, in collaborazione con l’Istituto Storico Germanico di Roma. Séguito del primo convegno dedicato a Roma religiosa (2008) – i cui
atti sono stati pubblicati nel 2009 nel numero 132 dell’Archivio della Società Romana di Storia Patria – ha centrato l’attenzione sul rapporto tra la società romana e il monachesimo cittadino con un taglio largamente diacronico – dal Tardo antico alla prima Età moderna – e con approccio volutamente multidisciplinare – dalla storia del libro a quella dell’arte, da tematiche di storia religiosa a problemi di gestione economica delle istituzioni monastiche
Quasi-periodic water waves
Full text linkWe present the result and the ideas of the recent paper (Berti and Montalto, Quasi-periodic standing wave solutions of gravity-capillary water waves, http://arxiv.org/abs/1602.02411, 2016) concerning the existence of Cantor families of small-amplitude time quasi-periodic standing wave solutions (i.e. periodic and even in the space variable x) of a 2-dimensional ocean, with infinite depth, in irrotational regime, under the action of gravity and surface tension at the free boundary. These quasi-periodic solutions are linearly stable. © 2016, Springer International Publishing
Quasi-periodic solutions for the forced Kirchhoff equation on T^d
Full text linkIn this paper we prove the existence of small-amplitude quasi-periodic solutions with Sobolev regularity, for the d-dimensional forced Kirchhoff equation with periodic boundary conditions. This is the first result of this type for a quasi-linear equation in high dimension. The proof is based on a Nash–Moser scheme in Sobolev class and a regularization procedure combined with a multiscale analysis in order to solve the linearized problem at any approximate solutio
Quasi-periodic incompressible Euler flows in 3D
Full text linkWe prove the existence of time-quasi-periodic solutions of the incompressible Euler equation on the three-dimensional torus T3, with a small time-quasi-periodic external force. The solutions are perturbations of constant (Diophantine) vector fields, and they are constructed by means of normal forms and KAM techniques for reversible quasilinear PDEs
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