Notiziario Scientifico

Notiziario dei seminari di carattere matematico
a cura del Dipartimento 'G. Castelnuovo'
Sapienza Università di Roma

Settimana dal 30 gennaio al 6 febbraio 2017


Lunedì 30 gennaio 2017
Ore 11:00, aula B
Incontro di lavoro su Calcolo delle Variazioni e Γ-convergenza/Working seminar on Calculus of Variations and Γ-convergence
Rufat Badal (TU Munich)
Gamma-convergence analysis of a generalized XY model: fractional vortices and string defects


Lunedì 30 gennaio 2017
Ore 14:30, aula di Consiglio
seminario di Analisi Matematica
Virginia Agostiniani (SISSA Trieste)
Plate models for thin soft active materials
We describe a couple of 'non-Euclidean' plate models and discuss their rigorous derivation from 3D systems characterised by kinematically incompatible spontaneous strains. The results presented are inspired by the modelling of ribbons of soft active materials, such as nematic elastomers or gels, which exhibit nontrivial bending configurations as states of (non-zero) minimal energy.


Lunedì 30 gennaio 2017
Ore 16:00, aula C
seminario BSD
Riccardo Salvati Manni (Sapienza Università di Roma)
Disco unitario generalizzato, semispazio superiore di Siegel, spazi di moduli di varietà abeliane


Martedì 31 gennaio 2017
Ore 14:00, aula G
seminario di Probabilità e Statistica
Valentina Cammarota (King's College, London)
On the critical values of random spherical harmonics
We study the limiting distribution, in the high energy limit, of critical points and extrema of random spherical harmonics. In particular, we first derive the density functions of extrema and saddles and then we provide analytic expressions for the variances. Our arguments require a careful investigation of the validity of the Kac-Rice formula in nonstandard circumstances, entailing degeneracies of covariance matrices for first and second derivatives of the processes being analyzed. It is well known that after proper rescaling random spherical harmonics converge to Berry's random plane waves; in the second part of the talk we focus on the spatial distribution of critical points of random plane waves. Based on joint works with Dmitry Beliaev, Domenico Marinucci and Igor Wigman.


Martedì 31 gennaio 2017
Ore 14:30, aula Dal Passo, Università di Roma Tor Vergata
seminario di Equazioni Differenziali
Andrea Braides (Università di Roma Tor Vergata)
Homogenization of geometric flows on lattices and a remark by De Giorgi
Gradient-flow type dynamics for spin systems give rise to motions of (crystalline) mean-curvature type with some features that are sometimes hard to foresee from the behaviour of the same systems in the static case. We give some examples after linking this issue to some late interests and a personal remark by De Giorgi, and to a commutativity theorem of gradient flow and Gamma-convergence


Martedì 31 gennaio 2017
Ore 15:00, aula G
seminario di Probabilità e Statistica
Sokol Ndreca (University Center of Belo Horizonte)
On a problem of Kendall
In this talk we consider a stochastic point process i+xi, where i∈N and the xi's are i.i.d exponential random variables with standard deviation σ. Some properties of this process are investigated. We then study a discrete time single server queueing system with this process as arrival process and deterministic unit service time. We obtain a functional equation of the bivariate probability generating function of the stationary distribution for the system. The functional equation is quite singular, does not admit simple solution. We find the solution of such equation on a subset of its set of definition. Finally we prove that the stationary distribution of the system decays super-exponentially fast in the quarter plane. The queueing model, motivated by air and railway traffic, has been proposed by Kendall and others some five decades ago, but no solution of it has been found so far. This is a joint work with Gianluca Guadagni, Carlo Lancia and Benedetto Scoppola.


Martedì 31 gennaio 2017
Ore 15:00, aula di Consiglio
seminario di Modellistica Differenziale Numerica
Yvain Queau (Technical University Munchen)
Nonlinear PDEs arising in photometric 3D-reconstruction: why they are unavoidable and how to handle them
Photometric 3D-reconstruction techniques aim at inferring the 3D geometry of a scene, given one or several 2D images of this scene. They do so by analyzing the luminous quantities in the images. A physics-based model for the observed colors is introduced, which describes the interactions between the geometry, the reflectance of the observed surface, the lighting and the camera. Then, this model needs to be inverted in each pixel so as to recover the geometry. In this talk, we describe some recent advances regarding modeling and resolution of shape-from-shading (single image) and photometric stereo (multiple images obtained under varying lighting). We show that resorting to PDEs is a natural way to cope with some of the arising ambiguities, but also to elegantly formulate the problem by reducing the number of unknowns and priors. Nevertheless, the resulting PDEs are usually nonlinear and cannot be solved exactly because of measurement noise. Hence, we discuss possible linearization strategies to make the problem tractable, as well as variational resolution schemes for ensuring robustness. Works in collaboration with Jean-Denis Durou (Université de Toulouse).


Mercoledì 1 febbraio 2017
Ore 20:30, aula Magna del Rettorato, Università di Roma Tre, v.le Ostiense 159
la Fisica incontra la Città
Fabio Bruni (Università di Roma Tre)
Cuocere quanto basta....ma quanto basta?
Pensare alla cucina come ad un vero e proprio laboratorio di fisica ci rende non solo maggiormente consapevoli dei vari processi fisici alla base della preparazione di cibi, ma anche (ed eventualmente) in grado di creare nuove e gustose ricette. Si parlerà quindi dell'equazione della diffusione del calore e della sua complicata soluzione, ma anche di diversi approcci per rispondere alla domanda nel titolo del seminario, basati su innovative tecniche di cottura o su modelli aleatori. Inoltre, proprietà fisiche come il modulo elastico e la pressione osmotica verranno usate per spiegare la formazione di emulsioni o per la preparazione della puntarella perfetta.


Giovedì 2 febbraio 2017
Ore 14:30, aula 211, Università di Roma Tre, l.go san L. Murialdo 1
seminario di Geometria
Tomoyuki Hisamoto (Nagoya University)
Coercivity of the K-energy and uniform K-stability
As a weak version of Yau-Tian-Donaldson conjecture, we expect that coercivity of the K-energy functional is equivalent to uniform K-stability. I would like to explain that this is true in the toric case.


Venerdì 3 febbraio 2017
Ore 16:00, aula Picone
seminario per Insegnanti (Piano Lauree Scientifiche)
Paolo Maroscia (Sapienza Università di Roma)
Matematica e Letteratura



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