Pagina 38

Date | Type | Start | End | Room | Speaker | From | Title |
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10/12/20 | Seminario | 16:00 | 17:00 | Carlangelo Liverani | Università di Roma "Tor Vergata" |
DinAmicI: Another Internet Seminar (DAI Seminar) Locating Ruelle-Pollicott resonances
- in streaming mode -
(see the instructions in the abstract)
We study the spectrum of transfer operators associated to various dynamical systems. Our aim is to obtain precise information on discrete spectrum. To this end we propose a unitary approach. We consider various settings where new information can be obtained following different branches along the proposed path. These settings include affine expanding Markov maps, uniformly expanding Markov maps, non-uniformly expanding maps, hyperbolic diffeomorphisms. We believe this to be the germ of a general theory. Joint work with O. Butterley and N. Kiamari.
Note:
The zoom link to the seminar will be posted on the DinAmicI website and on Mathseminars.org. Moreover, it will be also streamed live via the youtube DinAmicI channel.
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10/12/20 | Seminario | 14:00 | 15:00 | Gabriele Benedetti | Ruprecht-Karls-Universitat Heidelberg | Strong magnetic fields on surfaces: trapped motions and fully periodic systems It is a central problem in experimental physics to design magnetic fields that trap charged particles in a region of space. In this talk, we show how to use the KAM theorem to trap particles constrained on a surface if the magnetic field is strong and certain non-degenerate conditions on the field or on the curvature of the surface are satisfied. Using similar ideas we show that the motion of a particle in a strong magnetic field is periodic for every initial condition if and only if the field is constant and the surface has constant curvature.
This is joint work with Luca Asselle.
The talk is part of the activity of the MIUR Department of Excellence Project CUP E83C18000100006. | |

03/12/20 | Colloquium | 16:00 | 17:00 | Andrei Okounkov | Columbia University (NY, USA) |
Colloquium di Dipartimento ”Lie theory without groups”
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(see the link in the abstract)
Lie theory, which deals with smooth groups of transformations, is one of the cornerstones of mathematics and has great importance for both theory and applications. It is also visibly limited, as the globe of Lie groups has been explored and inhabited. However, in recent years, some new geometric and algebraic structures have been recognized as being as good as Lie groups in every respect, including e.g. their contribution to the supply of special functions. My goal in this talk will be to explain where these new avenues of Lie theory lead.
Note:
This talk is part of the activity of the MIUR Excellence Department Project MATH@TOV CUP
E83C18000100006
Link for the streaming (via Teams) | |

26/11/20 | Seminario | 17:00 | 18:00 | Anna Miriam Benini | Università di Parma | DinAmicI: Another Internet Seminar (DAI Seminar) Infinite entropy for transcendental entire functions
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(see the instructions in the abstract)
Defining entropy on noncompact metric spaces is a tricky business, since there are several natural and nonequivalent generalizations of the usual notions of entropy for continuous maps on compact spaces. By defining entropy for transcendental maps on the complex plane as the sup over the entropy restricted to compact forward invariant subsets, we prove that with this definition the entropy of such functions is infinite. The proof relies on covering results which are distinctive to holomorphic maps.
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26/11/20 | Seminario | 14:00 | 15:00 | Elsa Marchini | Politecnico di Milano | Minimal time optimal control for the moon lander problem We study a variant of the classical safe landing optimal control problem in aerospace, introduced by Miele in the Sixties, where the target was to land a spacecraft on the moon by minimizing the consumption of fuel. Assuming that the spacecraft has a failure and that the thrust (representing the control) can act in both vertical directions, the new target becomes to land safely by minimizing time, no matter of what the consumption is. In dependence of the initial data (height, velocity, and fuel), we prove that the optimal control can be of four different kinds, all being piecewise constant. Our analysis covers all possible situations, including the nonexistence of a safe landing strategy due to the lack of fuel or for heights/velocities for which also a total braking is insufficient to stop the spacecraft. N.B.: this talk is part of the activity of the MIUR Excellence Department Project CUP E83C18000100006 | |

19/11/20 | Seminario | 14:00 | 15:00 | Sara Daneri | Gran Sasso Science Institute | Symmetry breaking for local/nonlocal interaction functionals
In this talk I will review some recent results obtained in collaboration with E. Runa and A. Kerschbaum on the one-dimensionality of the minimizers of a family of continuous local/nonlocal interaction functionals in general dimension. Such functionals have a local term, typically the perimeter or its Modica-Mortola approximation, which penalizes interfaces, and a nonlocal term favouring oscillations which are high in frequency and in amplitude. The competition between the two terms is expected by experiments and simulations to give rise to periodic patterns at equilibrium. Functionals of this type are used to model pattern formation, either in material science or in biology. The difficulty in proving the emergence of such structures is due to the fact that the functionals are symmetric with respect to permutation of coordinates, while minimizers are not.
We will present new techniques and results showing that for two classes of functionals (used to model generalized anti-ferromagnetic systems, respectively colloidal suspensions), both in sharp interface and in diffuse interface models, minimizers are one-dimensional and periodic, in general dimension.
In the discrete setting such results had been previously obtained for a smaller set of functionals with a different approach by Giuliani and Seiringer.
N.B.: this talk is part of the activity of the MIUR Excellence Department Project CUP E83C18000100006
The seminar will be online at the following link | |

16/11/20 | Seminario | 14:00 | 15:00 | Isaia Nisoli | Universidade Federal de Rio de Janeiro (Brasile) | DinAmicI: Another Internet Seminar (DAI Seminar) A simple system presenting Noise Induced Order
- in streaming mode -
(see the instructions in the abstract)
In this talk I will present a family of one dimensional systems with random additive noise such that, as the noise size increases, the Lyapunov exponent of the stationary measure transitions from positive to negative. This phenomena is known in literature as Noise Induced Order, and was first observed in a model of the Belosouv-Zhabotinsky reaction and its existence was proven only recently by Galatolo-Monge-Nisoli. In the talk I will show how this phenomena is strictly connected with non-uniform hyperbolicity and the coexistence of regions of expansion and contraction in phase space; the result is attained through a result on the continuity of the Lyapunov exponent of the stationary measure with respect to the size of the noise.
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12/11/20 | Seminario | 16:00 | 17:00 | Stefano Marò | Università di Pisa | DinAmicI: Another Internet Seminar (DAI Seminar) Chaotic motion in the breathing circle billiard
- in streaming mode -
(see the instructions in the abstract)
We consider the free motion of a point particle inside a circular billiard with periodically moving
boundary, with the assumption that the collisions of the particle with the boundary are elastic so that the
energy of the particle is not preserved. It is known that if the motion of the boundary is regular enough
then the energy is bounded due to the existence of invariant curves. We show that it is nevertheless possible
that the motion of the particle is chaotic, also under regularity assumptions for the moving boundary. More
precisely, we show that there exists a class of functions describing the motion of the boundary for which
the billiard map admits invariant probability measures with positive metric entropy. The proof relies on
variational techniques based on Aubry-Mather theory. Joint work with Claudio Bonanno.
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12/11/20 | Seminario | 14:00 | 15:00 | Claudianor Alves | Università Federale di Campina Grande (Brasile) | Super-critical Neumann problems on unbounded domains In this paper, by making use of a new variational principle, we prove existence of nontrivial solutions for two different types of semilinear problems with Neumann boundary conditions in unbounded domains. Namely, we study elliptic equations and Hamiltonian systems on the unbounded domain $Omega=R^{m} imes B_r$ where $B_r$ is a ball centered at the origin with radius $r$ in $mathbb{R}^{n}$. Our proofs consist of several new and novel ideas that can be used in broader contexts. This is a joint work with Abbas Moameni that was accepted for publication in Nonlinearity.
N.B.: this talk is part of the activity of the MIUR Excellence Department Project CUP E83C18000100006.
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05/11/20 | Seminario | 16:30 | 17:30 | Adrian Perez Bustamante | Georgia Institute of Technology | Gevrey estimates and domains of analyticity for asymptotic expansions of tori in weakly dissipative systems We consider the problem of following quasi-periodic tori in perturbations of some Hamiltonian systems which involve friction and external forcing. In a first goal, we use different numerical methods (Pade approximants, Newton continuation till boundary) to obtain numerically the domain of convergence. We also study the properties of the asymptotic series of the solution. In a second goal, we study rigorously the (divergent) series of formal expansions of the torus obtained using Lindstedt method. We show that, for some systems in the literature, the series is Gevrey. We hope that the method can be of independent interest: we develop KAM estimates for the divergent series. In contrast with the regular KAM method, we lose control of all the domains, so that there is no convergence, but we can generate enough control to show that the series is Gevrey.
This is joint work with R. Calleja and R. de la Llave.
This activity is made in collaboration with the Departments of Mathematics of the Universities of Milano, Padova, Pisa and Roma Tor Vergata (Excellence Department project MATH@TOV). |

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