Seminario di Fenomenologia
Dr. Stefano Frixione (INFN Genova)
Although the computation of a vast class of $e^+e^-$ cross sections
is fully doable in perturbative QED, the perturbative series is not
well behaved unless a mechanism is devised that allows one to take
into account, to all orders in the coupling constant, the effects
due to multiple emissions of photons and $e^+e^-$ pairs off the
incoming particles. I shall discuss one such mechanism, that has
a strict analogy with its counterpart in QCD and is based upon
the so-called Parton Distribution Functions (PDFs) of the electron
and the positron. I shall present recent results that have improved
the accuracy to which these PDFs are known.
Our friend Carlo M. Becchi has turned 80 on October 20, 2019.
We invite all friends and colleagues to wish Carlo a very happy birthday and at the same time review his seminal contribution to theoretical physics and his role within the national and international community.
A ‘light’ workshop with both purposes will therefore take place at the Physics Department of the University of Genova on Feb. 4th, 2020
Seminario di Superconduttività Applicata
Dott. Fedor Gomory (Slovak Academy of Sciences)
Coated conductor (CC) tapes with functional REBCO (RE = Y, Gd, Er,…) layer exhibit unprecedented capability of transporting large amounts of electricity. Critical current, Ic, could reach e.g. 1000 A in a tape 12 mm wide when cooled down to 77 K. However, checking this property along the tape length quite often reveals the existence of locations with Ic value reduced to, say, 900 A. It is not obvious which of these two values should be considered the limitation for a steady long term operation. We expect that a current slightly surpassing the local critical value could be sustained, but at further increase of current the temperature will rise quickly creating the “hot spot” with enormous local dissipation causing an irreparable damage.
Analytical treatment of this electro-thermal problem has been performed. It was found that at surpassing the local Ic, the temperature could stabilize at an elevated value, because the dissipation is balanced by cooling capability of the environment. Then for a given tape architecture and cooling conditions one can find the value of transported current that triggers the development of hot spot. Advantage of this approach is rather simple way to compute the extent to which a tape is able to transport currents larger than the local minimum of critical current. Explicit formulas cover the dependence of hot spot development on the tape architecture and quality of cooling and in this way provide clear indications for an improvement of tape robustness.
Christiana Pantelidou (Trinity Dublin)
seminario fenomenologia: Fabrizio Caola (Oxford)
Seminario fisica teorica Andrea Amoretti (U. Genova)
Seminario di Fenomenologia Dr.ssa Carmelita Carbone (INAF Milano)
Seminario teorico: Alexander Krikun (Nordita Sweden)
Seminario fenomenologia: Matt LeBlanc (U. of Arizona/CERN)