Seminari/Colloquia
Pagina 29
Date  Type  Start  End  Room  Speaker  From  Title 

23/11/21  Seminario  16:00  17:00  1201 Dal Passo  Rafael SorianoLopez  Universidad Carlos III Madrid  Bound and ground states for an elliptic system with double criticality ( MS Teams Link for the streaming )
We will consider a nonlinear elliptic system in R^N. The interest of this problem is based on the presence of critical power nonlinearities and a nonlinear coupling, possibly critical, as well as Hardytype singular potentials. By means of variational methods, we will focus on the existence of solutions. More precisely, we shall derive new results on bound and ground states of the underlying energy functional. Finally, we extend our results to the special case of ''SchrödingerKortewegde Vries'' coupling type term.
This seminar is based on a couple of works in collaboration with Eduardo Colorado and Alejandro Ortega (UC3M).
NB:This talk is part of the activity of the MIUR Excellence Department Project MATH@TOV CUP E83C18000100006 
23/11/21  Seminario  14:30  15:30  1201 Dal Passo  Margherita Lelli Chiesa 
Let (S,L) be a general K3 surface of genus g. I will prove that the closure in L of the Severi variety parametrizing curves in L of geometric genus h is connected for h>=1 and irreducible for h>=4, as predicted by a well known conjecture. This is joint work with Andrea Bruno.
 
16/11/21  Seminario  14:00  15:00  1201 Dal Passo  Margarida Melo 
In the last few years, tropical methods have been applied quite successfully in understanding several aspects of the geometry of classical algebrogeometric moduli spaces. In particular, in several situations the combinatorics behind compactifications of moduli spaces have been given a tropical modular interpretation. Consequently, one can study different properties of these (compactified) spaces by studying their tropical counterparts.
In this talk, which is based in joint work with Madeleine Brandt, Juliette Bruce, Melody Chan, Gwyneth Moreland and Corey Wolfe, I will illustrate this phenomena for the moduli space Ag of abelian varities of dimension g. In particular, I will show how to apply the tropical understanding of the classical toroidal compactifications of Ag to compute, for small values of g, the top weight cohomology of Ag.
The techniques we use follow the breakthrough results and techniques recently developed by ChanGalatiusPayne in understanding the topology of the moduli space of curves via tropical geometry.
 
16/11/21  Seminario  13:00  14:00  1201 Dal Passo  Francesco Calabrò  Università degli Studi di Napoli Federico II  The use of artificial neural networks for the numerical solution of PDEs with collocation
Artificial neural networks are nowadays a widespread tool in applied mathematics for approximation and classification purposes. In this talk, we will survey recent results on the use of neural networks in computing the solution of PDEs. First of all, we introduce the use of network functions for the computation of forward and inverse problems for PDEs. Then, we will focus on collocation methods with feedforward neural network with a single hidden layer and sigmoidal transfer functions randomly generated, the socalled extreme learning machines. We will present results on elliptic problems both in the linear (with sharp gradient) case and for the construction of bifurcation diagrams of nonlinear problems.
The results are obtained in collaboration with Gianluca Fabiani and Costantinos Siettos.
This talk is part of the activity of the MIUR Excellence Department Project CUP E83C18000100006.
MS Teams link for the streaming 
12/11/21  Seminario  16:00  17:00  1201 Dal Passo  "Zetafunctions for class two nilpotent groups"  in live & streaming mode  (see the instructions in the abstract)
The notion of Zetafunction for groups was introduced in a seminal paper from Grunewald, Segal and Smith and proved to be a powerful tool to study the subgroup growth in some classes of groups.
In this seminar I will introduce this Zetafunction presenting some general properties for this object. I will then focus on some results obtained for class two nilpotent groups. I will in particular describe some combinatorial tecniques used to tackle this problem, namely the study of series associated to polyhedral integer cones. This is a joint work with Christopher Voll and Marlies Vantomme. N.B.: please click HERE to attend the talk in streaming  
12/11/21  Seminario  14:30  15:30  1201 Dal Passo  "On the multiplication of spherical functions of reductive spherical pairs"  in live & streaming mode  (see the instructions in the abstract)
Let G be a simple complex algebraic group and let K be a reductive subgroup of G such that the coordinate ring of G/K is a multiplicity free Gmodule. We consider the Galgebra structure of C[G/K], and study the decomposition into irreducible summands of the product of irreducible Gsubmodules in C[G/K]. We will present a conjectural decomposition rule for some special reductive pairs together with some partial results supporting the conjecture. We will explain how our conjecture would actually follow from an old conjecture of Stanley on the multiplication of Jack symmetric functions. We will also present a few new basic results related to Stanley's conjecture itself. The talk is based on a collaboration with Jacopo Gandini.
N.B.: please click HERE to attend the talk in streaming  
09/11/21  Seminario  16:00  17:00  1201 Dal Passo  Lorenza D'Elia  Università di Roma "Tor Vergata"  Homogenization of discrete thin structures (MS Teams link for the streaming at the end of the abstract)
We investigate discrete thin objects which are described by a subset $X$ of $mathbb{Z}^d imes {0,dots, M1 }^k$, for some $Minmathbb{N}$ and $d,kgeq 1$. We only require that $X$ is a connected graph and periodic in the first $d$directions. We consider quadratic energies on $X$ and we perform a discretetocontinuum and dimensionreduction process for such energies. We show that, upon scaling of the domain and of the energies by a small parameter $varepsilon$, the scaled energies $Gamma$converges to a $d$dimensional functional. The main technical points are a dimensionlowering coarsegraining process and a discrete version of the pconnectedness approach by Zhikov. This is a joint work with A. Braides.
MS Teams Link for the streaming Note: This talk is part of the activity of the MIUR Department of Excellence Project MATH@TOV CUP E83C18000100006 
09/11/21  Seminario  14:30  15:30  1201 Dal Passo  Roberto Pirisi 
Given an algebraic variety X, the Brauer group of X is the group of Azumaya algebras over X, or equivalently the group of SeveriBrauer varieties over X. While the Brauer group has been widely studied for schemes, computations at the level of moduli stacks are relatively recent, the most prominent of them being the computations by Antieau and Meier of the Brauer group of the moduli stack of elliptic curves over a variety of bases, including Z, Q, and finite fields. In a recent series of joint works with A. Di Lorenzo, we use the theory of cohomological invariants, and its extension to algebraic stacks, to completely describe the Brauer group of the moduli stacks of hyperelliptic curves, and their compactifications, over fields of characteristic zero, and the primetochar(k) part in positive characteristic. It turns out that the Brauer group of the noncompact stack is generated by elements coming from the base field, cyclic algebras, an element coming from a map to the classifying stack of étale algebras of degree 2g+2, and when g is odd by the BrauerSeveri fibration induced by taking the quotient of the universal curve by the hyperelliptic involution. This paints a richer picture than in the case of elliptic curves, where all nontrivial elements come from cyclic algebras. Regarding the compactifications, there are two natural ones, the first obtained by taking stable hyperelliptic curves and the second by taking admissible covers. It turns out that the Brauer group of the former is trivial, while for the latter it is almost as large as in the noncompact case, a somewhat surprising difference as the two stacks are projective, smooth and birational, which would force their Brauer groups to be equal if they were schemes.
 
02/11/21  Seminario  16:00  17:00  1201 Dal Passo  Stefano Pasquali  Lund University, Sweden  Chaoticlike transfers of energy in Hamiltonian PDEs (MS Teams link for the streaming at the end of the abstract)
A fundamental problem in nonlinear Hamiltonian PDEs on compact manifolds is understanding how solutions can exchange energy among Fourier modes. I will present a recent result which shows a new type of chaoticlike transfers of energy for the nonlinear cubic Wave, the Hartree and the nonlinear cubic Beam equation on the 2dimensional torus by combining techniques from dynamical systems and PDEs .
This mechanism is based on the existence of heteroclinic connections between invariant manifolds and on the construction of symbolic dynamics (Smale horseshoe) for the Birkhoff Normal Form truncation of those equations.
This is a joint work with F. Giuliani, M. Guardia and P. Martin (UPC, Barcelona).
MS Teams Link for the streaming Note: This talk is part of the activity of the MIUR Department of Excellence Project MATH@TOV CUP E83C18000100006 
02/11/21  Seminario  14:30  15:30  1201 Dal Passo  Peter Stevenhagen 
Let E be an elliptic curve defined over a number field K. Then for every prime p of K for which E has good reduction, the point group of E modulo p is a finite abelian group on at most 2 generators. If it is cyclic, we call p a prime of cyclic reduction for E. We will answer basic questions for the set of primes of cyclic reduction of E: is this set infinite, does it have a density, and can such a density be computed explicitly from the Galois representation associated to E? This is joint work with Francesco Campagna (MPIM Bonn).

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