24,570 research outputs found
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
, , and produced in Pb-Pb collisions at 158
GeV/. 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
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
Contribution of Galaxies to the Background Hydrogen-Ionizing Flux
We estimate the evolution of the contribution of galaxies to the cosmic
background flux at 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- (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- systems (DLA). We use these models to compute the
galactic contribution to the Lyman-limit emissivity and background flux for . 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 . Though the resulting galaxy flux
is completely negligible at high redshifts, it is comparable to the quasar flux
at .Comment: 14 pages, 5 figures, requires mn.sty, accepted for publication in
MNRA
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
On the possible tools for the prevention of non-performing loans. A case study of an Italian bank
This work analyses the contribution of an Information Systems (IS) to the implementation of credit monitoring as a new integrated process to prevent non-performing loans in a small bank. The study focuses on the process of active monitoring of the entire credit portfolio, aimed at guiding the best migration between risk classes. This is understood as a set of integrated activities, in which the quality of information becomes a major determinant of the outcome. Such tools support risk management in the decision-making process and aiding performance evaluation. The purpose of this work is to highlight the possibility of an IS to support this new integrated process of credit monitoring, providing increasingly reliable data, availability on demand and real-time information
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
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