arXiv subjects

P. Costa

Publications and source records attributed to P. Costa.

10 recordsLinked to original sources

arXiv2025

CaNS-Fizzy: A GPU-accelerated finite difference solver for turbulent two-phase flows

CaNS-Fizzy -- Fizzy for short -- is a GPU-accelerated numerical solver for massively-parallel Direct Numerical Simulations (DNS) of incompressible two-phase flows. A DNS enables direct access to all flow quantities, resolved in time and space at all relevant continuum scales. The resulting numerical experiments provide complete data sets for the analysis of the detailed mechanisms underlying the flow, particularly the interaction between the chaotic and multi-scale dynamics of turbulence and the interface movement and deformation. The insights gained can guide the design and operation of various applications, such as boiling heat transfer, liquid-liquid extraction, gas-liquid reactors, absorption and stripping columns, distillation columns, liquid combustion appliances, in all of which the rate of heat and mass transfer between phases is proportional to the interfacial area. Fizzy's two-phase capabilities were implemented using the efficient, GPU-accelerated Navier-Stokes solver CaNS as base.

physics.flu-dyn↗

arXiv2023

Temperature and Strong Magnetic Field Effects in Dense Matter

We study consistently the effects of magnetic field on hot and dense matter. In particular, we look for differences that arise due to assumptions that reproduce the conditions produced in particle collisions or astrophysical scenarios, such as in the core of fully evolved neutron stars (beyond the protoneutron star stage). We assume the magnetic field to be either constant or follow a profile extracted from general relativity calculations of magnetars and make use of two realistic models that can consistently describe chiral symmetry restoration and deconfinement to quark matter, the Chiral Mean Field (CMF) and the Polyakov-loop extended Nambu-Jona-Lasinio (PNJL) models. We find that net isospin, net strangeness, and weak chemical equilibrium with leptons can considerably change the effects of temperature and magnetic fields on particle content and deconfinement in dense matter. We finish by discussing the possibility of experimentally detecting quark deconfinement in dense and/or hot matter and the possible role played by magnetic fields.

nucl-th↗

arXiv2019

Exploration of the phase diagram and the thermodynamic properties of QCD at finite temperature and chemical potential with the PNJL effective model

The QCD transition from a hadronic to a quark-gluon plasma phase is a cross-over at vanishing/small baryo-chemical potential, while at higher chemical potentials it is argued that it becomes of first order, ending with a critical end-point. The present goal is the determination of the critical line and, possibly, the recognition of the critical endpoint. For this purpose, the effective model (Nambu-Jona-Lasinio model with Polyakov Loop) with 2+1 flavours is used. In Mean Field Approximation it is possible to obtain all thermodynamic quantities (pressure, entropy, energy and quark density) and their fluctuations, in particular, the generalized quark-number susceptibilities. We use the net baryon-number fluctuations and net-strangeness fluctuations to identify the critical line and the order of the phase transition in the chemical potential - temperature plane.

hep-ph↗

arXiv2019

Solar flare forecasting using morphological properties of sunspot groups

We describe a new tool developed for solar flare forecasting on the base of some sunspot group properties. Assuming that the flare frequency follows the Poisson statistics, this tool uses a database containing the morphological characteristics of the suspot groups daily observed by the Equatorial Spar of INAF $-$ Catania Astrophysical Observatory since January 2002 up today. By means of a linear combination of the flare rates computed on the base of some properties of the sunspot groups, like area, number of pores and sunspots, Zurich class, relative importance between leading spot and density of the sunspot population, and type of penumbra of the main sunspot, we determine the probability percentages that a flare of a particular energy range may occur. Comparing our forecasts with the flares registered by GOES satellites in the 1$-$8 \AA{} X$-$ray band during the subsequent 24 hrs we measured the performance of our method. We found that this method, which combines some morphological parameters and a statistical technique, has the best performances for the strongest events, which are more interesting for their implications in the Earth environment.

astro-ph.SR↗

arXiv2018

Homologous white light solar flares driven by photosperic shear motions

We describe the peculiarity of two recurrent white light flares occurred on Sept. 06, 2017, in the super Active Region (SAR) NOAA 12673, with a time interval, between their peaks, of about 3 hours. These events of X2.2 and X9.3 GOES class are very important not only for their high level of emission and for the visible effects on the lower layers of the solar atmosphere, discernible as clear white light ribbons, but as well for the strong horizontal photospheric motions which seemed to drive them. In fact, we observed for several hours before the flare occurrence the displacement of a negative umbra located in the main delta spot of the Active Region. We measured velocities up to 0.6 km s$^{-1}$. The strong and persistent shear motion of the photospheric structures together with the high intensity of the magnetic flux involved by these events can be considered responsible for the new energy continuously supplied into the magnetic system. From the timing of the emissions at different wavelengths we were able to provide some constraints for the modeling of such events.

astro-ph.SR↗

arXiv2016

Drag reduction in turbulent channel flow laden with finite-size oblate spheroids

We study suspensions of oblate rigid particles in a viscous fluid for different values of the particle volume fractions. Direct numerical simulations have been performed using a direct-forcing immersed boundary method to account for the dispersed phase, combined with a soft-sphere collision model and lubrication corrections for short-range particle-particle and particle-wall interactions. With respect to the single phase flow, we show that in flows laden with oblate spheroids the drag is reduced and the turbulent fluctuations attenuated. In particular, the turbulence activity decreases to lower values than those obtained by only accounting for the effective suspension viscosity. To explain the observed drag reduction we consider the particle dynamics and the interactions of the particles with the turbulent velocity field and show that the particle wall layer, previously observed and found to be responsible for the increased dissipation in suspensions of spheres, disappears in the case of oblate particles. These rotate significantly slower than spheres near the wall and tend to stay with their major axes parallel to the wall, which leads to a decrease of the Reynolds stresses and turbulence production and so to the overall drag reduction.

physics.flu-dyn↗

arXiv2015

Inverse Magnetic Catalysis in hot quark matter within (P)NJL models

Apart from Magnetic Catalysis at low temperatures, recent LQCD studies have shown the opposite effect at temperatures near the transition region: instead of enhancing, the magnetic field suppresses the quark condensates (Inverse Magnetic Catalysis). In this paper, two approaches are discussed within NJL-type models with Polyakov Loop that reproduce both effects.

hep-ph↗

arXiv2014

Inverse magnetic catalysis in the (2+1)-flavor Nambu--Jona-Lasinio and Polyakov--Nambu--Jona-Lasinio models

The QCD phase diagram at zero chemical potential and finite temperature subject to an external magnetic field is studied within the three flavor Nambu--Jona-Lasinio (NJL) model and the NJL model with the Polyakov loop (PNJL). A scalar coupling parameter dependent on the magnetic field intensity is considered. The scalar coupling has been fitted so that the lattice QCD pseudocritical chiral transition temperatures are reproduced and in the limit of large magnetic field decreases with the inverse of the magnetic field intensity. This dependence of the coupling allows to reproduce the lattice QCD results with respect to the quark condensates and Polyakov loop: due to the magnetic field the quark condensates are enhanced at low and high temperatures and suppressed for temperatures close to the transition temperatures and the Polyakov loop increases with the magnetic field.

hep-ph↗

arXiv2012

Some properties of two Nambu--Jona-Lasinio -type models with inputs from lattice QCD

We investigate the phase diagram of the so-called Polyakov--Nambu--Jona-Lasinio (PNJL) model at finite temperature and nonzero chemical potential. The calculations are performed in the light and strange quark sectors ($u$, $d$, $s$), which includes the 't Hooft instanton induced interaction term that breaks the axial symmetry, and the quarks are coupled to the (spatially constant) temporal background gauge field. On one hand, a special attention is payed to the critical end point (CEP). The strength of the flavor-mixing interaction alters the CEP location, since when it becomes weaker the CEP moves to low temperatures and can even disappear. On the other hand, we also explore the connection between QCD, a nonlocal Nambu--Jona-Lasinio type model and the Landau gauge gluon propagator. Possible links between the quenched gluon propagator and low energy hadronic phenomenology are investigated.

hep-ph↗

arXiv2011

D mesons at finite temperature and density in the PNJL model

We study D meson resonances in hot, dense quark matter within the NJL model and its Polyakov-loop extension. We show that the mass splitting between D^+ and D^- mesons is moderate, not in excess of 100 MeV. When the decay channel into quasifree quarks opens (Mott effect) at densities above twice saturation density, the decay width reaches rapidly the value of 200 MeV which entails a spectral broadening sufficient to open J/psi dissociation processes. Contrary to results from hadronic mean-field theories, the chiral quark model does not support the scenario of a dropping D meson masses so that scenarios for J/psi dissociation by quark rearrangement built on the lowering of the threshold for this process in a hot and dense medium have to be reconsidered and should account for the spectral broadening.

hep-ph↗