Transverse mass distributions of strange particles produced in Pb-Pb collisions at 158 A GeV/c

Experiment NA57 has collected high statistics, high purity samples of $K^0_s$, $\Lambda$, $\Xi$ and $\Omega$ produced in Pb-Pb collisions at 158 $A$ GeV/$c$. In this paper we present a study of the transverse mass spectra of these particles for a sample of events corresponding to about the most central 55% of the inelastic Pb-Pb cross section. We analyse the transverse mass distributions in the framework of the blast-wave model for the full sample under consideration and, for the first time at the SPS, as a function of the event centrality.Comment: Contribution to the International Workshop on QCD: QCD@Work 2003 - Conversano (Italy) 14-18 June 2003 (eConf C030614

Results on Lambda and Xi production in Pb-Pb collisions at 160 GeV/c per nucleon from the NA57 experiment

The NA57 experiment has been designed to study the onset of enhanced production of strange baryons and anti-baryons in Pb-Pb collisions with respect to p-Be collisions. This enhancement is considered a sensitive signature for a phase transition to a new state of matter -- the Quark Gluon Plasma (QGP). In this paper, we report results on Lambda and Xi hyperon production in central Pb-Pb collisions at 160 GeV/c per nucleon beam momentum.Comment: To be published in the proceedings of The XXXVIIth Rencontres de Moriond "QCD And High Energy Hadronic Iinteractions". n. of pages:6. n. of figures:

ALICE results on heavy-ion physics at the LHC

ALICE is a multipurpose detector for high-energy nucleus-nucleus physics at the CERN Large Hadron Collider (LHC). In November 2010, ALICE took its first Pb-Pb data at the centre-of-mass energy of 2.76TeV per nucleon pair; reference data in proton-proton collisions at the same energy and at 7TeV were collected in 2010 and 2011. A second, higher statistics Pb-Pb run took place in fall 2011. An overview of the main physics results is presented

Contribution of Galaxies to the Background Hydrogen-Ionizing Flux

We estimate the evolution of the contribution of galaxies to the cosmic background flux at $912 \AA$ by means of a semi-analytic model of galaxy formation and evolution. Such a modelling has been quite successful in reproducing the optical properties of galaxies. We assume hereafter the high-redshift damped Lyman-$\alpha$ (DLA) systems to be the progenitors of present day galaxies, and we design a series of models which are consistent with the evolution of cosmic comoving emissivities in the available near infrared (NIR), optical, ultraviolet (UV), and far infrared (FIR) bands along with the evolution of the neutral hydrogen content and average metallicity of damped Lyman-$\alpha$ systems (DLA). We use these models to compute the galactic contribution to the Lyman-limit emissivity and background flux for $0 \simeq z \le 4$. We take into account the absorption of Lyman-limit photons by HI and dust in the interstellar medium (ISM) of the galaxies. We find that the background Lyman-limit flux due to galaxies might dominate (or be comparable to) the contribution from quasars at almost all redshifts if the absorption by HI in the ISM is neglected. The ISM HI absorption results in a severe diminishing of this flux--by almost three orders of magnitude at high redshifts to between one and two orders at $z \simeq 0$. Though the resulting galaxy flux is completely negligible at high redshifts, it is comparable to the quasar flux at $z \simeq 0$.Comment: 14 pages, 5 figures, requires mn.sty, accepted for publication in MNRA

Chiral two-dimensional electron gas in a periodic magnetic field

We study the energy spectrum and electronic properties of two-dimensional electron gas in a periodic magnetic field of zero average with a symmetry of triangular lattice. We demonstrate how the structure of electron energy bands can be changed with the variation of the field strength, so that we can start from nearly free electron gas and then transform it continuously to a system of essentially localized chiral electron states. We find that the electrons near some minima of the effective potential are responsible for occurrence of dissipationless persistent currents creating a lattice of current contours. The topological properties of the electron energy bands are also varied with the intensity of periodic field. We calculated the topological Chern numbers of several lower energy bands as a function of the field. The corresponding Hall conductivity is nonzero and, when the Fermi level lies in the gap, it is quantized.Comment: 10 pages;9 figures;42 reference

Sampling-Based Query Re-Optimization

Despite of decades of work, query optimizers still make mistakes on "difficult" queries because of bad cardinality estimates, often due to the interaction of multiple predicates and correlations in the data. In this paper, we propose a low-cost post-processing step that can take a plan produced by the optimizer, detect when it is likely to have made such a mistake, and take steps to fix it. Specifically, our solution is a sampling-based iterative procedure that requires almost no changes to the original query optimizer or query evaluation mechanism of the system. We show that this indeed imposes low overhead and catches cases where three widely used optimizers (PostgreSQL and two commercial systems) make large errors.Comment: This is the extended version of a paper with the same title and authors that appears in the Proceedings of the ACM SIGMOD International Conference on Management of Data (SIGMOD 2016

The determinants of land use in Italy from a spatial perspective: A re-interpretation at the time of Covid-19

Since the post-Second World War period, territorial development in Italy has been characterised by unsustainable settlement patterns, including the unplanned and wildfire growth of urban systems and the propensity to overbuilding. Systematic knowledge of the key aspects of land use patterns is the basis for planning sustainable land development. Furthermore, the outbreak of the COVID-19 pandemic has accentuated the need to re-address land management to ensure public safety and protection. By using the Spatial Durbin Model (SDM), this work aims to: i) analyse the determinants that best quantitatively describe land use patterns in Italian municipalities; ii) provide a re-interpretation of the main results in light of the territorial re-planned process required by the Covid-19 pandemic. The results suggest that monitoring land use and strengthening quality and cooperation between local institutions are needed to preserve the environment and ecosystem services that underlie more sustainable land use planning