Weekly Seminars for June 2008

Wednesday 11th June 2008 

Università "La Sapienza Roma - Aula 8 (Dip. Fisica N.E.)

Speaker: Prof. Charles W. Misner from University of Maryland, College Park, Maryland USA and currently ICRANet Pescara

Title: John A Wheeler's rescue of Einstein's gravitation theory

Abstract: In the 1930s and 1940s Einstein's general relativity (gravitation) theory was mostly regarded as irrelevant to "real" physics. This was due in part to the lack of new experiments and to the uncertainty of cosmological data. But it also reflected a distaste for most efforts to follow Einstein's lead in seeking a unified field theory in ways that ignored the (then) new particles -- neutrons, positrons, neutrinos, and eventually mesons -- and the non-electromagnetic forces they implied. From the early 1950s through the mid 1970s Wheeler was the most effective among those seeking to have general relativity revitalized by compatibility with current physics and prospects for new experiments and by new expectations for the content of this theory. His leadership style in producing new generations of physicists is emphasized.

Presentation: PPT

Friday 13th June 2008

Università "La Sapienza" Roma - Aula Rasetti (2° p. Dip. Fisica V.E.)

Speaker: Dr. Stefano Covino from Osservatorio Astronomico di Brera (INAF)

Title: The Exceptionally Bright GRB080319B

Abstract: The Swift satellite has revolutionised GRB science providing a wealth of new data which forced researchers in the field to change established views. Beyond providing high-quality observations for hundreds of GRBs, Swift was also able to detect an exceptional event: GRB080319B. This GRB is known to have reached during the prompt phase an unprecedented brightness in the optical. It could have been visible with the naked eye for a few tens of seconds. Moreover, the lucky occurrence of a previous GRB about half an hour before, at about 10 degrees from the GRB080319B position, allowed wide-field cameras to follow the optical emission during the prompt phase even before the GRB alert was delivered by Swift. Together with the multiwavelength coverage of the prompt phase, the brightness of the afterglow allowed us to derive a rich dataset in the X-ray and optical/NIR. We now review these data and discuss the proposed interpretations in the context of the beamed fireball scenario.

Presentation: PPT

Friday 13th June 2008

Università "La Sapienza" Roma - Aula 6 (Dip. Fisica N.E.)

Speaker: Prof. Guido Barbiellini from INFN, Sez. Trieste

Title: Fulmini e Saette

Abstract: The astrophysical Mission AGILE is on a low equatorial orbit at 550 Km above sea level since April 23 2007 when was launched from the Indian base of Sriharicota close to Chennai (ancient Madras) in the south region of India. The instruments on board of AGILE are able to detect high energy photons coming from everywhere in the energy range from 0.1 to1000 Mev. This electromagnetic waves are usually denominated X and Gamma rays and due to very short wave length the interaction enhance their particles behaviour. Many important astrophysical observations are already obtained in this first year of observation. During the time of earth observation, due to solar energy constrains, the AGILE telescope has detected gamma emission coming from below, very short (~1msec) and of high intensity ~ 100 counts on a surface of ~100 cm2 . The very same phenomenon has been observed in the 90 by the NASA Space mission dedicated to Compton (CGRO). This fast gamma flash (TGF) only recently (2006) has been related to lightning. A very precise time coincidence between the burst timing and an electromagnetic antenna sensible to the electromagnetic field originated by the discharge has proven the common source of the two phenomena. The electric field associated to the cloud of a thunderstorm or in to the different regions of our atmosphere are in general lower of the electric air breakdown so the lightning need a trigger . Recently has been suggested that the extensive air showers initiated by the cosmic rays in the atmosphere can play this role. The fast ionization due to the EAS creates the free electrons seed for the discharge. The electrons have to reach in a short time a relativistic energy in order to minimize the energy losses in the air. The detection of energetic photons with an energy spectrum compatible with that of a bremsstrahlung from 30 Mev electrons ,is in agreement with the previous suggestion. The formation of the different kinds of lightnings is a very complex phenomenon that imply the contribution of many recent scientific discoveries not known to our ancestors that ascribed the lightning to the Zeus's fury. From the sky Zeus was sending to earth burning arrows prepared in large series by Vulcano. This was a satisfactory possibility.


Saturday 14th June 2008

ICRANet Pescara, Seminars Room

Speaker: Diego J. Cirilo Lombardo from Bogoliubov Laboratory of Theoretical Physics, Joint Institute of Nuclear Research, Dubna - Russia

Title: New spherically symmetric monopole and regular solutions in Einstein-Born-Infield theory

Abstract: In this work a new asymptotically flat solution of the coupled Einstein-Born-Infeld equations for a static spherically symmetric space-time is obtained. When the intrinsic mass is zero the resulting spacetime is regular everywhere, in the sense given by B. Hoffmann and L. Infeld in 1937, and the Einstein-Born-Infeld theory leads to the identification of the gravitational with the electromagnetic mass. This means that the metric, the electromagnetic field and their derivatives have not discontinuities in all the manifold. In particular, there are not conical singularities at the origin, in contrast to well known monopole solution studied by B. Hoffmann in 1935. The lack of uniqueness of the action function in Non-Linear-Electrodynamics is discussed.

Presentation: PPT

Wednesday 25th June 2008

Università "La Sapienza" Roma - Aula Rasetti (2° piano Dip. Fisica Ed. Marconi)

Speaker: Dr. Alessandro Cardinali from Associazione EURATOM-ENEA sulla Fusione, Sezione Teoria

Title: Tecniche asintotiche nello studio della propagazione di onde elettromagnetiche ad alta frequenza in mezzi ionizzati

Abstract: Lo studio della propagazione e dell'assorbimento di onde elettromagnetiche ad alta frequenza in gas ionizzati sottoposti a campi magnetici esterni, e' descritto dal sistema di equazioni integro-differenziali di Maxwell-Vlasov. Sotto opportune condizioni il sistema Maxwell-Vlasov puo essere ricondotto ad equazioni piu trattabili sia analiticamente sia numericamente. Medoti asintotici di tipo WKB applicati alle equazioni modello permettono inoltre di ottenere analiticamente e numericamente le soluzioni e di studiare i limiti di validita' delle tecniche asintotiche. Il carattere Hamiltoniano delle equazioni modello, che derivano dall'analisi WKB, permette di sfruttare la teoria perturbativa dei sistemi Hamiltoniani e delle trasformazioni canoniche nella ricerca delle soluzioni analitiche. L'approccio numerico alla soluzione delle equazioni invece deve essere orientato alla costruzione di algoritmi che conservino il carattere simplettico del sistema Hamiltoniano. Saranno discussi i risultati e le soluzioni trovate analiticamente e numericamente.