Gianluca Gregori

Abstract:

By performing an ensemble of molecular dynamics simulations, the model-dependent ionization state is computed for strongly interacting systems self-consistently. This is accomplished through a free energy minimization framework based on the technique of thermodynamic integration. To illustrate the method, two simple models applicable to partially ionized hydrogen plasma are presented in which pair potentials are employed between ions and neutral particles. Within the models, electrons are either bound in the hydrogen ground state or distributed in a uniform charge-neutralizing background. Particular attention is given to the transition between atomic gas and ionized plasma, where the effect of neutral interactions is explored beyond commonly used models in the chemical picture. Furthermore, pressure ionization is observed when short-range repulsion effects are included between neutrals. The developed technique is general, and we discuss the applicability to a variety of molecular dynamics models for partially ionized warm dense matter.

Abstract:

Cosmic rays (CRs) play a pivotal role in shaping the thermal and dynamical properties of astrophysical environments, such as galaxies and galaxy clusters. Recent observations suggest a stronger confinement of CRs in certain astrophysical systems than predicted by current CR-transport theories. Here, we show that the incorporation of microscale physics into CR-transport models can account for this enhanced CR confinement. We develop a theoretical description of the effect of magnetic microscale fluctuations originating from the mirror instability on macroscopic CR diffusion. We confirm our theory with large-dynamical-range simulations of CR transport in the intracluster medium (ICM) of galaxy clusters and kinetic simulations of CR transport in micromirror fields. We conclude that sub-teraelectronvolt CR confinement in the ICM is far more effective than previously anticipated on the basis of Galactic-transport extrapolations. The transformative impact of micromirrors on CR diffusion provides insights into how microphysics can reciprocally affect macroscopic dynamics and observable structures across a range of astrophysical scales.

Abstract:

Data used for the generation of the figures

Abstract:

Recent archaeological research in the Valle Sabbia in the territory of Brescia (BS-Northern Italy) has led to the discovery of a new place of worship from the Roman era, possibly built on an ancient indigenous sanctuary. The Valle Sabbia is one of the alpine valleys of Lombardy, north of Brescia (the Colonia Augusta Civica Brixia). The territory, crossed by the river Chiese, stretches between Lake Idro and Lake Garda, in a favourable geographical position that puts it in direct contact with the plain on one side and the Alps on the other. Since 2000, campaigns of archaeological excavations have led to the discovery of different contexts that can be interpreted as sacred, with frequenting from prehistoric times to Roman times and which have as recurrent characteristic a close relationship with the surrounding landscape, with a clear preference for mountainous and wooded contexts. The most important novelties, concerning the Roman period, emerge in Villanuova sul Clisi, where on a panoramic hill overlooking the entire Valle Sabbia and Garda Lake, various wall structures have emerged that define a complex built on several levels, with a rectangular main room of about 11×4,20 m, made with large structures confining the summit plateau, and other lateral ones. The recovered materials indicate a visitation from the 1st to the 4th century A.D.: in addition to coins, fibulae and ceramics, some miniature metal ex-voto with dedications to Iuppiter Aeternus, various graffiti on plaster and a stone altar also inscribed have been uncovered.

Abstract:

The pursuit of inertial confinement fusion ignition target designs requires precise experimental validation of the conditions within imploding capsules, in particular the density and temperature of the compressed shell. Previous work has identified x-ray Thomson scattering (XRTS) as a viable diagnostic tool for inferring the in-flight compressed deuterium-tritium shell conditions during capsule implosions (Poole et al 2022 Phys. Plasmas 29 072703). However, this study focused on one-dimensional simulations, which do not account for the growth of hydrodynamic instabilities. In this work, two-dimensional DRACO simulations incorporating intermediate-mode perturbations up to Legendre mode ℓ=50 were used to generate synthetic XRTS spectra with the SPECT3D code. The analysis employed Markov-Chain Monte Carlo techniques to infer plasma conditions from these spectra. The results demonstrate that the XRTS diagnostic platform can effectively discern the in-flight compressed shell conditions for targets with varying adiabats, even in the presence of intermediate-mode perturbations. This work underscores the potential of XRTS for realistic inertial confinement fusion experiments, providing a robust method for probing the complex dynamics of fusion implosions.