Interaction corrections: temperature and parallel field dependencies of the Lorentz number in two-dimensional disordered metals

The electron-electron interaction corrections to the transport coefficients are calculated for a two-dimensional disordered metal in a parallel magnetic field via the quantum kinetic equation approach. For the thermal transport, three regimes (diffusive, quasiballistic and truly ballistic) can be identified as the temperature increases. For the diffusive and quasiballistic regimes, the Lorentz number dependence on the temperature and on the magnetic field is studied. The electron-electron interactions induce deviations from the Wiedemann-Franz law, whose sign depend on the temperature: at low temperatures the long-range part of the Coulomb interaction gives a positive correction, while at higher temperature the inelastic collisions dominate the negative correction. By applying a parallel field, the Lorentz number becomes a non-monotonic function of field and temperature for all values of the Fermi-liquid interaction parameter in the diffusive regime, while in the quasiballistic case this is true only sufficiently far from the Stoner instability.Comment: 11 pages, 5 figures. Appendix A revised, notes adde

Il rapporto fra stato e regioni al tempo del coronavirus: una premessa

L’emergenza sanitaria ha evidenziato una serie di problemi in ordine al reciproco ascolto ed all’adeguata determinazione degli ambiti di competenza attribuiti allo Stato ed alle regioni, già latenti in precedenza ed ulteriormente sviluppati in questa fase. Da qui la necessità di rispondere ad alcune domande essenziali sul ruolo svolto dallo Stato e dalle regioni durante questo periodo di emergenza per verificare come il sistema ha funzionato e per capire le prospettive futur

Riforme costituzionali per garantire la stabilità governativa

Si apre una nuova stagione di riforme costituzionali? Dinanzi alle varie ipotesi di riforma che vengono prospettate, quella che più di altre necessita un intervento innovatore riguarda il ruolo e le caratteristiche del Presidente del Consiglio dei ministri. Il rafforzamento dei suoi poteri costituisce un elemento imprescindibile in un contesto europeo e per un corretta organizzazione della Presidenza del Consiglio e di tutto il suo governo

L’accentramento del potere decisionale nel governo e le fonti di gestione dell’emergenza sanitaria

The topics analyzed in this paper concern the methods of action of the government during the emergency and, in particular, the use of the sources of law during this period. The anomalies of these two profiles use reverberate in the post-Covid period and in particular in the phase of development and implementation of the New Generation Italy (PNRR)

Multibody Models for the Analysis of a Fall From Height: Accident, Suicide, or Murder?

The final subject position is often the only evidence in the case of the fall of a human being from a given height. Foreseeing the body trajectory and the respective driving force may not be trivial due to the possibility of rotations and to an unknown initial position and momentum of the subject. This article illustrates how multibody models can be used for this aim, with specific reference to an actual case, where a worker fell into a stair well, prior to stair mounting, and he was found in an unexpected posture. The aim of the analysis was establishing if this worker was dead in that same place, if he had been pushed, and which was his initial position. A multibody model of the subject has been built (“numerical android”), given his stature and his known mass. Multiple simulations have been performed, following a design of experiments where various initial positions and velocity as well as pushing forces have been considered, while the objective function to be minimized was the deviation of the numerical android position from the actual worker position. At the end of the analysis, it was possible to point how a very limited set of conditions, all including the application of an external pushing force (or initial speed), could produce the given final posture with an error on the distance function equal to 0.39 m. The full analysis gives a demonstration of the potentiality of multibody models as a tool for the analysis of falls in forensic inquiries

Extreme High-Field Superconductivity in Thin Re Films

We report the high-field superconducting properties of thin, disordered Re films via magneto-transport and tunneling density of states measurements. Films with thicknesses in the range of 9 nm to 3 nm had normal state sheet resistances of $\sim$0.2 k$\Omega$ to $\sim$1 k$\Omega$ and corresponding transition temperatures in the range of 6 K to 3 K. Tunneling spectra were consistent with those of a moderate coupling BCS superconductor. Notwithstanding these unremarkable superconducting properties, the films exhibited an extraordinarily high upper critical field. We estimate their zero-temperature $H_{c2}$ to be more than twice the Pauli limit. Indeed, in 6 nm samples the estimated reduced critical field $H_{c2}/T_c\sim$ 5.6 T/K is among the highest reported for any elemental superconductor. Although the sheet resistances of the films were well below the quantum resistance $R_Q=h/4e^2$, their $H_{c2}$'s approached the theoretical upper limit of a strongly disordered superconductor for which $k_F\ell\sim1$.Comment: 12 pages, 10 figure