174 research outputs found
Composition and thermodynamics of nuclear matter with light clusters
We investigate nuclear matter at finite temperature and density, including
the formation of light clusters up to the alpha particle The novel feature of
this work is to include the formation of clusters as well as their dissolution
due to medium effects in a systematic way using two many-body theories: a
microscopic quantum statistical (QS) approach and a generalized relativistic
mean field (RMF) model. Nucleons and clusters are modified by medium effects.
Both approaches reproduce the limiting cases of nuclear statistical equilibrium
(NSE) at low densities and cluster-free nuclear matter at high densities. The
treatment of the cluster dissociation is based on the Mott effect due to Pauli
blocking, implemented in slightly different ways in the QS and the generalized
RMF approaches. We compare the numerical results of these models for cluster
abundances and thermodynamics in the region of medium excitation energies with
temperatures T <= 20 MeV and baryon number densities from zero to a few times
saturation density. The effect of cluster formation on the liquid-gas phase
transition and on the density dependence of the symmetry energy is studied.
Comparison is made with other theoretical approaches, in particular those,
which are commonly used in astrophysical calculations. The results are relevant
for heavy-ion collisions and astrophysical applications.Comment: 32 pages, 15 figures, minor corrections, accepted for publication in
Physical Review
1-2-3-flavor color superconductivity in compact stars
We suggest a scenario where the three light quark flavors are sequentially
deconfined under increasing pressure in cold asymmetric nuclear matter, e.g.,
as in neutron stars. The basis for our analysis is a chiral quark matter model
of Nambu--Jona-Lasinio (NJL) type with diquark pairing in the spin-1 single
flavor (CSL) and spin-0 two/three flavor (2SC/CFL) channels, and a
Dirac-Brueckner Hartree-Fock (DBHF) approach in the nuclear matter sector. We
find that nucleon dissociation sets in at about the saturation density, n_0,
when the down-quark Fermi sea is populated (d-quark dripline) due to the flavor
asymmetry imposed by beta-equilibrium and charge neutrality. At about 3n_0
u-quarks appear forming a two-flavor color superconducting (2SC) phase, while
the s-quark Fermi sea is populated only at still higher baryon density. The
hybrid star sequence has a maximum mass of 2.1 M_sun. Two- and three-flavor
quark matter phases are found only in gravitationally unstable hybrid star
solutions.Comment: 4 pages, 2 figures, to appear in the proceedings of Quark Matter
2008: 20th International Conference on Ultra-Relativistic Nucleus Nucleus
Collisions (QM 2008), Jaipur, India, 4-10 Feb 200
Mobility patterns of the elderly tourist in Algarve
The present work is part of the Project for Scientific Research and Techno-logical Development "Accessibility for All in Tourism" focuses on modal in-terfaces designed according to the concepts of "Universal Design" and "Age Sensitive Design". In this project 851 surveys were carried out for elderly tourists, who arrived in Algarve (Portugal) through the international Airport of Faro, in the summer of 2018, with a view to understanding their prefer-ences and needs in terms of mobility. It presents the characterization of the senior tourist in Algarve, according to: gender, age, academic qualification, situation in the relation to the profession, nationality, disability and/or disa-bilities that affects mobility and the need to use technical aids to move. It analyses and compares, from the point of view of sustainable mobility, the mobility of the elderly tourist, by gender and age group, in the country where they reside and in the Algarve region. This information is useful for local au-thorities and for transport operators in order to make the mobility of elderly tourists, in Algarve, more sustainable from a social, economic and environ-mental standpoint.The Research Project ACCES4ALL - Accessibility for All in Tourisminfo:eu-repo/semantics/publishedVersio
Core collapse supernovae in the QCD phase diagram
We compare two classes of hybrid equations of state with a hadron-to-quark
matter phase transition in their application to core collapse supernova
simulations. The first one uses the quark bag model and describes the
transition to three-flavor quark matter at low critical densities. The second
one employs a Polyakov-loop extended Nambu-Jona-Lasinio (PNJL) model with
parameters describing a phase transition to two-flavor quark matter at higher
critical densities. These models possess a distinctly different temperature
dependence of their transition densities which turns out to be crucial for the
possible appearance of quark matter in supernova cores. During the early post
bounce accretion phase quark matter is found only if the phase transition takes
place at sufficiently low densities as in the study based on the bag model. The
increase critical density with increasing temperature, as obtained for our PNJL
parametrization, prevents the formation of quark matter. The further evolution
of the core collapse supernova as obtained applying the quark bag model leads
to a structural reconfiguration of the central proto-neutron star where, in
addition to a massive pure quark matter core, a strong hydrodynamic shock wave
forms and a second neutrino burst is released during the shock propagation
across the neutrinospheres. We discuss the severe constraints in the freedom of
choice of quark matter models and their parametrization due to the recently
observed 2 solar mass pulsar and their implications for further studies of core
collapse supernovae in the QCD phase diagram.Comment: 19 pages, 4 figures, CPOD2010 conference proceedin
How strange are compact star interiors ?
We discuss a Nambu--Jona-Lasinio (NJL) type quantum field theoretical
approach to the quark matter equation of state with color superconductivity and
construct hybrid star models on this basis. It has recently been demonstrated
that with increasing baryon density, the different quark flavors may occur
sequentially, starting with down-quarks only, before the second light quark
flavor and at highest densities also the strange quark flavor appears. We find
that color superconducting phases are favorable over non-superconducting ones
which entails consequences for thermodynamic and transport properties of hybrid
star matter. In particular, for NJL-type models no strange quark matter phases
can occur in compact star interiors due to mechanical instability against
gravitational collapse, unless a sufficiently strong flavor mixing as provided
by the Kobayashi-Maskawa-'t Hooft determinant interaction is present in the
model. We discuss observational data on mass-radius relationships of compact
stars which can put constraints on the properties of dense matter equation of
state.Comment: 7 pages, 2 figures, to appear in the Proceedings of the International
Conference SQM2009, Buzios, Rio de Janeiro, Brazil, Sep.27-Oct.2, 200
Strange Exotic States and Compact Stars
We discuss the possible appearance of strange exotic multi-quark states in
the interior of neutron stars and signals for the existence of strange quark
matter in the core of compact stars. We show how the in-medium properties of
possible pentaquark states are constrained by pulsar mass measurements. The
possibility of generating the observed large pulsar kick velocities by
asymmetric emission of neutrinos from strange quark matter in magnetic fields
is outlined.Comment: 10 pages, invited talk given at the International Conference on
Strangeness in Quark Matter 2006 (SQM2006), UCLA, USA, March 26-31, 2006,
Journal of Physics G in press, refs. adde
Constraining mean-field models of the nuclear matter equation of state at low densities
An extension of the generalized relativistic mean-field (gRMF) model with
density dependent couplings is introduced in order to describe thermodynamical
properties and the composition of dense nuclear matter for astrophysical
applications. Bound states of light nuclei and two-nucleon scattering
correlations are considered as explicit degrees of freedom in the
thermodynamical potential. They are represented by quasiparticles with
medium-dependent properties. The model describes the correct low-density limit
given by the virial equation of state (VEoS) and reproduces RMF results around
nuclear saturation density where clusters are dissolved. A comparison between
the fugacity expansions of the VEoS and the gRMF model provides consistency
relations between the quasiparticles properties, the nucleon-nucleon scattering
phase shifts and the meson-nucleon couplings of the gRMF model at zero density.
Relativistic effects are found to be important at temperatures that are typical
in astrophysical applications. Neutron matter and symmetric matter are studied
in detail.Comment: 50 pages, 21 figure
Equation of State of Nuclear Matter at high baryon density
A central issue in the theory of astrophysical compact objects and heavy ion
reactions at intermediate and relativistic energies is the Nuclear Equation of
State (EoS). On one hand, the large and expanding set of experimental and
observational data is expected to constrain the behaviour of the nuclear EoS,
especially at density above saturation, where it is directly linked to
fundamental processes which can occur in dense matter. On the other hand,
theoretical predictions for the EoS at high density can be challenged by the
phenomenological findings. In this topical review paper we present the
many-body theory of nuclear matter as developed along different years and with
different methods. Only nucleonic degrees of freedom are considered. We compare
the different methods at formal level, as well as the final EoS calculated
within each one of the considered many-body schemes. The outcome of this
analysis should help in restricting the uncertainty of the theoretical
predictions for the nuclear EoS.Comment: 51 pages, to appear in J. Phys. G as Topical Revie
Phase diagrams in nonlocal PNJL models constrained by Lattice QCD results
Based on lattice QCD-adjusted SU(2) nonlocal Polyakov--Nambu--Jona-Lasinio
(PNJL) models, we investigate how the location of the critical endpoint in the
QCD phase diagram depends on the strenght of the vector meson coupling, as well
as the Polyakov-loop (PL) potential and the form factors of the covariant
model. The latter are constrained by lattice QCD data for the quark propagator.
The strength of the vector coupling is adjusted such as to reproduce the slope
of the pseudocritical temperature for the chiral phase transition at low
chemical potential extracted recently from lattice QCD simulations. Our study
supports the existence of a critical endpoint in the QCD phase diagram albeit
the constraint for the vector coupling shifts its location to lower
temperatures and higher baryochemical potentials than in the case without it.Comment: 23 pages, 10 figures. Version accepted in Phys. Part. Nucl. Lett. (to
appear), references adde
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