Ciclo di Conferenze dei corsi di Laurea in Fisica del Dipartimento di Matematica e Fisica
Edizione 2015
Andrea Fabbri
Università Roma Tre & INFN
Le radiazioni ionizzanti in fisica medica: dalla diagnosi alla terapia
Link identifier #identifier__35837-1Locandina – 13 gennaio 2015, ore 15:00 Aula C
Il seminario introduce all’utilizzo delle radiazioni ionizzanti negli strumenti diagnostici, quali SPECT (Single Photon Computed Tomography) e PET (Positron Emission Tomography), nonché agli sviluppi in corso per apparati sempre più specifici e mirati ai singoli organi. In ambito terapeutico l’utilizzo di fotoni ed elettroni ad elevata energia è ormai uno strumento di uso quotidiano per i medici e i fisici sanitari nei reparti di radioterapia. Le nuove tecnologie che prevedono l’utilizzo di protoni e di ioni carbonio aprono nuovi orizzonti nella cura al cancro. Il gruppo di ricerca di Roma Tre lavora da anni su diverse applicazioni di fisica medica: dallo sviluppo di gamma camere per applicazioni SPECT, con particolare attenzione ad apparati compatti ad uso chirurgico ed a tomografi di nuova generazione. Altro filone di ricerca riguarda la misura della dose in radioterapia e nelle nuove tecniche di adroterapia. La parte attiva del dispositivo di misura è basato su sensori in diamante sintetico monocristallino che permette misure affidabili e ripetibili di elettroni, fotoni e protoni in un ampissimo spettro di energie.
Andrea Bizzarri
INGV Bologna
The Physics of Earthquakes: What We Have Understood in 50 Years and What We Can Do Now
Link identifier #identifier__129417-2Locandina – 3 febbraio 2015, ore 15:00 Aula C
The Physics of the earthquake source is undoubtedly a relatively juvenile discipline. Significant (conceptual) progresses have been made since the early ‘60s in the ambitious attempt to understand the plethora of physico–chemical, potentially competing, processes taking place during a faulting episode. Contrary to other fields of science, seismology can not plan experiments at the scale and in the conditions of the natural phenomenon and thus it has to rely on the data collected after real earthquakes. Laboratory experiments, conducted under restrictive conditions due to technical limitations, give general information which have to be scaled to the real–world. Geological (field) observations are inherently limited by the frequent inaccessibility of the seismogenic structures. On the other hand, theoretical and numerical models represent a powerful and complementary view of the problem, since they make it possible to explore, in realistic conditions, the energy–dissipating mechanisms occurring on the fault zones. The grand challenge of seismology definitively is the earthquake prediction, but efforts at doing this, based on the relatively incomplete understanding we have of the physics of earthquakes, have failed. Models of seismic ruptures can definitively represent an important contribution in this framework. We will present and discuss the results of state–of–the–art numerical experiments of synthetic earthquake events, with the special aim to illustrate the origin of the slip complexity and the pivotal role of the governing models assumed to govern the traction evolution on a fault. A complete picture of the fault constitutive models available for a deterministic description of earthquakes will be given; open issues and future developments will be also illustrated.
Pavel Winternitz
Université de Montréal
Superintegrability and exact solvability. Concepts and perspectives
Link identifier #identifier__68978-3Locandina – 3 marzo 2015, ore 15:00 Aula C
A review is given of the present status of superintegrable systems, i.e. finite dimensional classical and quantum Hamiltonian systems with more integrals of motion than degrees of freedom. The emphasis is on conceptual questions and on recent developments such as the discovery of infinite families of superintegrable systems with integrals of motion of arbitrary order in the momenta. Superintegrable systems involving particles with spin will be introduced.
Valeria Ferrari
Dipartimento di Fisica “G. Marconi” Sapienza, Università di Roma
Cento anni di Relatività Generale: dalle prime verifiche alla ricerca delle onde gravitazionali
Link identifier #identifier__170774-4Locandina – 22 aprile 2015, ore 15:00 Aula C
A dispetto dell’età, la teoria della Relatività Generale gode ancora di ottima salute. La prima verifica osservativa di una delle sue predizioni, la deflessione della luce in presenza di corpi massivi, fu effettuata da Eddington, Dayson and Davidson durante l’eclisse di Sole nel 1919. Da allora, le misure di redshift delle linee spettrali di oggetti compatti, dell’effetto lente gravitazionale, del trascinamento dei riferimenti inerziali dovuto alla rotazione dei corpi, l’osservazione di buchi neri supermassivi al centro delle galassie e lo studio dettagliato del moto delle pulsar binarie, per citare alcune delle osservazioni astrofisiche più importanti, hanno permesso di verificare la validità della teoria e delle sue predizioni. Inoltre, gli esperimenti per verificare la validità del principio di equivalenza su cui la teoria si basa, si sono susseguiti negli anni arrivando a precisioni sempre maggiori. Ma le onde gravitazionali sfuggono ancora a una rivelazione diretta, sebbene le osservazioni del moto delle pulsar binarie abbiano dimostrato che esistono. Riusciremo a catturarle con i rivelatori interferometrici Virgo e LIGO che stanno per entrare in funzione?
Luca Biferale
Università di Roma Tor Vergata
Una visita guidata attraverso la turbolenza in 2D, in 3D e in dimensioni intermedie
Link identifier #identifier__1757-5Locandina – 5 maggio 2015, ore 15:00 Aula C
In this seminar, I will discuss a few important open problems in “Fully Developed Turbulence” concerning its most idealised realisation, i.e. the case of statistically homogeneous and isotropic flows. I will discuss the importance of inviscid conserved quantities in relation to the most striking statistical properties shown by all turbulent flows: the growth of small-scales strongly non-Gaussian fluctuations, including the presence of anomalous scaling laws. By using unconventional numerical methodology, based on a Galerkin decimation of Fourier modes, I will argue that some phenomena characterising homogeneous and isotropic flows might be important also for a much larger spectrum of applications, including flows with geophysical and astrophysical relevance as for the case of rotating turbulence and/or conducting fluids.
Marco Grilli
Sapienza Università di Roma
Superconductivity and Quantum Criticality
Link identifier #identifier__152408-6Locandina – 23 giugno 2015, ore 15:00 Aula C
Although it was discovered more than a century ago, superconductivity (SC) still keeps its charm and is one of the most actively investigated subjects in condensed-matter physics. Our understanding of SC rests on two milestone paradigms: the Landau theory of normal Fermi liquids and the Bardeen-Cooper-Schrieffer (BCS) theory of SC. The former describes the metallic state where sizably interacting electrons give eventually rise to weakly interacting “quasiparticles”. According to the BCS theory, these nearly free quasiparticles are then paired by the attractive forces mediated by the phonons, thereby forming singlet pairs with opposite momentum. As soon as they are formed, these electron pairs condense in a coherent macroscopic quantum state giving rise to the superconducting phase. In the last three decades, both these “classical” paradigms have been challenged and an increasingly long list of materials has been found, where the metallic phase seems not to be a Fermi liquid and SC emerges in some anomalous way. One quite common feature of these anomalous superconducting systems is that the concept of quantum criticality is somehow involved in their strange physical properties. This talk aims to briefly revise the above traditional concepts to contrast the anomalous metallic and superconducting behaviors of these new materials, which are described emphasizing their intriguing proximity to quantum criticality.
Paolo De Bernardis
Dipartimento di Fisica – Sapienza Università di Roma
Cosmic Microwave Background Cosmology
Link identifier #identifier__180617-7Locandina – 15 settembre 20215, ore 15:00 Aula C
Precision measurements of the CMB provide essential information on all phases of the evolution of the Universe: from inflation to galaxy clusters, and all its components. In this talk we review the observables and measurement techniques, we report selected recent results from the Planck mission, and describe two experiments: the forthcoming italian balloon-borne LSPE (Large Scale Polarization Explorer), and the ambitious “final” CMB mission COrE++, to be proposed to ESA.
Vincenzo Artale
ENEA, C.R. Frascati
The Thermohaline Circulation: New Problems and Prospects on its Study and Numerical Simulation Focusing in Particular on the Mediterranean Ocean Circulation
Link identifier #identifier__93549-8Locandina – 13 ottobre 2015, ore 15:00 Aula B
Since of the ’50s Stommel’s pioneeristic works, the dominant paradigm of the ocean conveyor belt is based on the concept that the horizontal pressure forces resulting from the hydrostatically balanced horizontal density differences drive the ocean flow. More recently, many studies have revitalized the role of the ocean’s eddy and wind field in establishing the characteristic and variability of the global thermohaline circulation. These recent finding reconcile Stommel theory with the modeling results of ’70 regarding the effect of eddies on the deep flow, still an important component of the THC. Moreover the THC, due to the intrinsic heterogeneity and nonlinearity of the ocean circulation, describable by many variables that vary significantly over space and time scale covering many order of magnitude, if only due to the dominance of advective fluxes within the ocean water 3-D domains, but also to the many complex feedback between the domains. As consequence positive (negative) feedback can lead to instability that drives the system to new modes of behaviour that bear little resemblance to the external forcing, if such destabilising processes are not properly represented, the ocean circulation, for example simulated in the OGCM, may not able to display important observed modes of ocean internal variability. In this talk we review those studies, which collectively, are changing the classical view of the global conveyor belt; in particular we discuss how these results have had an influence on some recent theoretical and numerical results on the Mediterranean thermohaline circulation and on its future development.
Mario Vietri
Scuola Normale Superiore
On the late evolution of binary pulsars’ magnetospheres
Link identifier #identifier__114659-9Locandina – 3 novembre 2015, ore 15:00 Aula B
I will discuss the magnetospheric interaction of inspiraling binary pulsars in their late stages of evolution, right before their merger. The compression of the magnetosphere induces powerful electric fields which cannot be screened by any distribution of charges and currents. When the inspiraling induced by gravitational waves has brought the two stars to some critical radius, the induction electric field generates a pair plasma, which leads to a catastrophic collapse of the nearly steady state solution. This releases an outflow of pair-dominated plasma with an energy density roughly equivalent to that stored in the magnetic field; however, since the currents creating the field are safely stored inside the stars, this process repeats itself as a wind, giving rise to a potentially observable phenomenon which is identical to a short GRB in terms of total energy release and burst duration.