| 18/05/22 | Seminario | 14:00 | 15:00 | 2001 | Tom Lyche | University of Oslo | A C1 simplex spline basis for the Alfeld split
Piecewise polynomials over triangles and tetrahedrons have applications in several branches ranging from finite element analysis, surfaces in computer aided design... The smoothness on tetrahedrons is obtained either by high degrees of polynomials or using smaller degrees when splitting the tetraehedron into smaller pieces. Here we consider the Alfeld split which generalizes the Clough-Tocher split of a triangle. Simplex splines with arbitrary knots are the natural generalization of univariate B-splines to several variables. We consider degrees d = 2s-1 in dimension s and construct a partition of unity basis for the space S12s-1;s on the Alfeld split, consisting of simplex-splines. We also show a Marsden like identity for s ≤ 5.
Joint work with Jean-Louis Merrien.
This talk is part of the activity of the MIUR Excellence Department Project CUP E83C18000100006. |
| 17/05/22 | Seminario | 16:00 | 17:00 | 1201 Dal Passo | Chaona Zhu | Chinese Academy of Sciences and Roma "Tor Vergata" | Prescribing scalar curvatures: the negative case
( MS Teams Link for the streaming )
The problem of prescribing conformally the scalar curvature on a closed manifold of negative Yamabe invariant is always solvable, if the function to be prescribed is strictly negative, while sufficient and necessary conditions are known in the case that function is non positive. Still in the case of a negative Yamabe invariant, Rauzy (Trans. Amer. Math. Soc. 1995) showed solvability, if the function to be prescribed is not too positive, as quantified by Aubin-Bismuth (J. Funct. Anal. 1997) later on. In this talk we will review these results variationally and shed some light on the case, when Rauzy’s conditions fail. This talk is joint work with Martin Mayer.
NB:This talk is part of the activity of the MIUR Excellence Department Project MATH@TOV CUP E83C18000100006
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| 13/05/22 | Colloquium | 15:00 | 16:00 | 1201 Dal Passo | Michela Procesi | Università di Roma Tre | May12: Celebrating Women in Maths
Order and chaos and wave dynamics
(Opening address by Gabriella Tarantello)
(MS Teams link for the streaming at the end of the abstract)
Many physical phenomena are well described as the propagation of waves: the motion of the sea, the transmission of sound, electromagnetic waves (light, radio waves). Their mathematical description is often extremely complicated, and characterized by the coexistence of stable and chaotic behaviors. I will discuss some models of wave propagation by nonlinear Partial Differential Equations illustrating briefly the main difficulties as well as some mathematical methods used to study them.
A small refreshment will be served at the end of the colloquium.
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 |
| 10/05/22 | Seminario | 16:00 | 17:00 | 1201 Dal Passo | Filippo Gazzola | Politecnico di Milano | Long-time behavior of partially damped systems modeling degenerate plates with piers
( MS Teams Link for the streaming )
We consider a partially damped nonlinear beam-wave system of evolution PDE's modeling the dynamics of a degenerate plate. The plate can move both vertically and torsionally and, consequently, the solution has two components. We show that the component from the damped beam equation always vanishes asymptotically while the component from the (undamped) wave equation does not. In case of small energies we show that the first component vanishes at exponential rate. Our results highlight that partial damping is not enough to steer the whole solution to rest and that the partially damped system can be less stable than the undamped system. Hence, the model and the behavior of the solution enter in the framework of the so-called "indirect damping" and "destabilization paradox". These phenomena are valorized by a physical interpretation leading to possible new explanations of the Tacoma Narrows Bridge collapse.
Joint work with Abdelaziz Soufyane (University of Sharjah, UAE)
NB:This talk is part of the activity of the MIUR Excellence Department Project MATH@TOV CUP E83C18000100006 |
| 10/05/22 | Colloquium | 14:30 | 15:30 | 1201 Dal Passo | Slava Rychkov | IHES, Bures sur Yvette, Paris |
COLLOQUIUM LEVI-CIVITA
“Bootstrap” method in physics and
mathematics
In the last 10-15 years, “bootstrap” was applied to problems as disparate as critical exponents of second-order phase transitions, scattering of elementary particles, chaotic dynamical systems, and Laplacian spectra on hyperbolic manifolds. This produced many new computer-assisted bounds on various quantities of interest. I will explain common features of these problems, and what is this bootstrap method which applies to all of them. |
| 09/05/22 | Colloquium | 15:00 | 16:00 | 1201 Dal Passo | Lorenzo Rosasco | University of Genova | A guided tour of machine learning (theory)
In this talk, we will provide a basic introduction to some of the fundamental ideas and results in machine learning, with emphasis on mathematical aspects. We will begin contrasting the modern data driven approach to modeling to classic mechanistic approaches. Then, we will discuss basic elements of machine learning theory connected to approximation theory, probability and optimization. Finally, we will discuss the need of new theoretical advances at the light of recent empirical observations while using deep neural networks. |
| 06/05/22 | Seminario | 14:30 | 15:30 | 1201 Dal Passo | Peter FIEBIG | Friedrich-Alexander-Universität Erlangen-Nürnberg |
Algebra & Representation Theory Seminar (ARTS)
"Tilting modules and torsion phenomena"
- in live & streaming mode -
( click HERE to attend the talk in streaming )
N.B.: this talk is part of the activity of the MIUR Excellence Department Project CUP E83C18000100006
Given a root system and a prime number p we introduce a category X of “graded spaces with Lefschetz operators” over a ring A. Then we show that under a base change morphism from A to a field K this category specialises to representations of the hyperalgebra of a reductive group, if K is a field of positive characteristic, and of a quantum group at pl-th root of unity, if K is the pl-th cyclotomic field. In this category we then study torsion phenomena (over the ring A) and construct for any highest weight a family of universal objects with certain torsion vanishing condi-tions. By varying these conditions, we can interpolate between the Weyl modules (maximal torsion) and the tilting objects (no torsion). This construction might shed some light on the character generations philosophy of Lusztig and Lusztig-Williamson.
N.B.: please click HERE to attend the talk in streaming.
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| 04/05/22 | Seminario | 14:00 | 15:00 | 2001 | Marjeta Knez | University of Ljubljana | A super-smooth C1 spline space over planar mixed triangle and quadrilateral meshes
In the talk a C1 spline space over mixed meshes composed of triangles and quadrilaterals, suitable for FEM-based or isogeometric analysis, will be introduced. The mesh is considered to be a partition of a planar polygonal domain into triangles and/or quadrilaterals. The proposed space combines the Argyris triangle element with the C1
quadrilateral element for polynomial degrees d ≥ 5. The spline space is assumed to be C2 at all vertices and C1 across edges, and the splines are uniquely determined by C2-data at the vertices, values and normal derivatives at chosen points on the edges, and values at some additional points in the interior of the elements.
The motivation for combining the Argyris triangle element with a recent C1 quadrilateral construction, inspired by isogeometric analysis, is two-fold: on one hand, the ability to connect triangle and quadrilateral finite elements in a C1 fashion is non-trivial and of theoretical interest. On the other hand, the construction facilitates the meshing process by allowing more flexibility while remaining C1 everywhere. This is for instance relevant when trimming of tensor-product B-splines is performed.
As it will be demonstrated by numerical examples the presented spline space can be employed to various applications like interpolation and least square approximation of a given function or to solve the biharmonic equation via its weak form and Galerkin discretization.
This talk is part of the activity of the MIUR Excellence Department Project CUP E83C18000100006. |
| 03/05/22 | Seminario | 16:00 | 17:00 | 1201 Dal Passo | Francesco Fidaleo | Università di Roma | Spectral actions for q-particles and their asymptotic
( MS Teams Link for the streaming )
For spectral actions made of the average number of particles and arising fromopen systems made of general free q-particles (including Bose, Fermi and classical ones corresponding to q= pm 1 and 0, respectively) in thermal equilibrium, we compute the asymptotic expansion with respect to the natural cut-off. We treat both relevant situations relative to massless and massive particles, where the natural cut-off is 1/eta=k_eta T and 1//sqrt{eta}, respectively. We show that the massless situation enjoys less regularity properties than the massive one. We also consider the passage to the continuum describing infinitely extended open systems in thermal equilibrium. We briefly discuss the appearance of condensation phenomena occurring for Bose-like q-particles, for which qin (0,1], after passing to the continuum. We also compare the arising results for the finite volume situation (discrete spectrum) with the corresponding infinite volume one (continuous spectrum).
NB:This talk is part of the activity of the MIUR Excellence Department Project MATH@TOV CUP E83C18000100006 |
| 22/04/22 | Seminario | 16:00 | 17:00 | 1201 Dal Passo | Andrea APPEL | Università di Parma |
Algebra & Representation Theory Seminar (ARTS)
"Schur-Weyl duality for quantum affine symmetric pairs"
- in live & streaming mode -
( please click HERE to attend the talk in streaming )
N.B.: This talk is part of the activity of the MIUR Excellence
Department Project MATH@TOV CUP E83C18000100006
In the work of Kang, Kashiwara, Kim, and Oh, the Schur-Weyl duality between quantum affine algebras and affine Hecke algebras is extended to certain Khovanov-Lauda-Rouquier (KLR) algebras, whose defining combinatorial datum is given by the poles of the normalised R-matrix on a set of representations.
In this talk, I will review their construction and introduce a "boundary" analogue, consisting of a Schur-Weyl duality between a quantum symmetric pair of affine type and a modified KLR algebra arising from a (framed) quiver with a contravariant involution. With respect to the Kang-Kashiwara-Kim-Oh construction, the extra combinatorial datum we take into account is given by the poles of the normalised K-matrix of the quantum symmetric pair.
N.B.: please click HERE to attend the talk in streaming.
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