Young Seminars SIFS

La SIFS organizza gli Young Seminars SIFS su temi vari connessi alla Fisica Statistica, come attività culturale per dare uno spazio ai ricercatori più giovani, ovvero studenti, dottorandi e coloro che hanno ricevuto il titolo di dottorato da meno di 5 anni.

I seminari hanno cadenza mensile, con due interventi nella stessa sessione, e saranno poi resi disponibili online tramite il canale Youtube ufficiale della SIFS, per chi fosse interessato e non riuscisse a seguirli in diretta.

I
seminari non saranno troppo ed esclusivamente tecnici, ma saranno dedicati anche ad un'introduzione generale sulla tematica affrontata.

I colloquia sono tenuti online sulla piattaforma Microsoft Teams.

Istuzioni per partecipare ai Seminars

  • prima dell'orario stabilito per il seminario verrà pubblicato nella Home del sito web della SIFS e su questa pagina, il link per poter accedere al meeting su Teams;

  • chiunque può accedere al meeting semplicemente cliccando sul link, anche in assenza di un account Teams o Microsoft. Consigliamo fortemente l'uso di Google Chrome che è completamente supportato da Teams, mentre altri browsers potrebbero dare problemi;

  • una volta cliccato sul link è sufficiente seguire le indicazioni, inserendo un nome per essere individuabili nella riunione. Vi chiediamo di accedere alla riunione spegnendo videocamera e microfono prima di entrare o immediatamente, in modo da alleggerire la piattaforma;

  • i seminari verranno registrati, per essere reso accessibile successivamente tramite il canale Youtube SIFS: partecipando alla riunione date il consenso per la registrazione;

  • in ogni sessione si terranno due seminari di mezz'ora ciascuno, con 25 minuti riservati al talk vero e 5 minuti riservati alle domande.

Upcoming Seminars

Modelling Immune Recognition with Restricted Boltzmann Machines

Barbara Bravi, Laboratoire de Physique, École Normale Supérieure Paris


Abstract: The immune response of an organism when it is infected by a pathogen is based on the recognition of small portions of its proteins. This raises two questions: what protein portions are relevant to this process? And what immune cells are able to recognize them? In this talk, I will discuss models to answer those two questions that are based on the machine learning method known as Restricted Boltzmann Machine and that are learned from large protein sequence datasets. These models provide flexible and interpretable frameworks to characterize and predict immune recognition of both cancer and infections.

Date: 11th February 2021 - 16.30 Rome Time

Getting hotter by heating less: how driven granular materials dissipate energy in excess

Andrea Plati, Sapienza Università di Roma


Abstract: A fundamental question in systems driven out of thermodynamic equilibrium is how the properties of the Non Equilibrium Stationary States (NESS) are related to the specific mechanisms by which external energy is supplied. Vibro-fluidized granular matter, where a NESS is reached through a balance between the energy injected by a mechanical vibration and the dissipation due to inelastic collisions, represents a good context to tackle this problem.

In this talk, we present experimental and numerical results about the relation between the kinetic energy acquired by a driven dense granular system and the input energy. Our focus is on the dependence of the granular behavior on two main parameters: frequency and vibration amplitude. We find that there exists an optimal forcing frequency, at which the system reaches the maximal kinetic energy: if the input energy is increased beyond such a threshold, the system dissipates more and more energy and recovers a colder and more viscous state. Studying dissipative properties of the system, we unveil a striking difference between this nonmonotonic behavior and a standard resonance mechanism. This feature is also observed at the microscopic scale of the single-grain dynamics and can be interpreted as an instance of negative specific heat. An analytically solvable model based on a generalized forced-damped oscillator well reproduces the observed phenomenology, illustrating the role of the competing effects of forcing and dissipation.


Date: 11th February 2021 - 16.30 Rome Time

Past Seminars

Spatial patterns in the velocity field of Active Matter systems

Lorenzo Caprini, University of Camerino


Abstract: Many systems of biological or technological interest, such as bacterial colonies or cell monolayers, show spatial patterns in their velocity field without displaying a global polarization. In this talk, we investigate this phenomenon through a non-equilibrium stochastic dynamics, the so-called Active Brownian Particles (ABP), which is one of the most popular minimal models to describe the behavior of several experimental active particles. We report the first evidence that pure repulsive spherical ABP, without alignment interactions, spontaneously form large domains of particles with aligned velocities, both in homogeneous dense phases and phase-separated regimes. The size of the velocity domains is measured through the correlation length of the spatial velocity correlations whose shape is analytically predicted. We unveil the non-thermal nature of this collective phenomenon that, instead, is induced by the interplay between steric interactions and active forces, also highlighting the dynamical role played by inertial forces. The results are summarized in a non-equilibrium phase diagram, packing fraction vs persistence time, where the structural properties of the system (distinguishing active liquid, hexatic and solid phases) are superimposed with the velocity correlation lengths. The presence of the almost-translational order typical of hexatic and solid configurations plays a crucial role and reveals an interesting scenario which also involves intermittency phenomena in the time-trajectory of the kinetic energy.

Date: 14th January 2021 - 16.30 Rome Time

Synthetic models for quantum many-body physics out of equilibrium

Lorenzo Piroli, Max-Planck-Institut für Quantenoptik


Abstract: It has been known for a long time that thermalization is associated with "chaotic'' behavior at the microscopic level, although a quantitative understanding of its key mechanisms from fundamental theories poses formidable challenges. This problem can be effectively tackled in isolated many-body quantum systems, where the absence of interactions with the environment allows us to gain valuable insight from both first-principle calculations, and quantum simulation experiments. In this talk, I will review recent studies aiming at capturing the most relevant aspects of thermalization processes using theoretical "quantum circuit" models for the many-body dynamics, which are inspired by ideas of quantum simulation by quantum computers. In particular, I will focus on how standard tools in statistical mechanics have been successfully employed for obtaining nontrivial analytic results in this context.

Date: 14th January 2021 - 16.30 Rome Time