90 research outputs found
Spin polarized neutron matte and magnetic susceptibility within the Brueckner-Hartree-Fock approximation
The Brueckner--Hartree--Fock formalism is applied to study spin polarized
neutron matter properties. Results of the total energy per particle as a
function of the spin polarization and density are presented for two modern
realistic nucleon-nucleon interactions, Nijmegen II and Reid93. We find that
the dependence of the energy on the spin polarization is practically parabolic
in the full range of polarizations. The magnetic susceptibility of the system
is computed. Our results show no indication of a ferromagnetic transition which
becomes even more difficult as the density increases.Comment: 15 pages, 4 figures (Submitted to PRC
Spin-orbit and tensor interactions in homogeneous matter of nucleons: accuracy of modern many-body theories
We study the energy per particle of symmetric nuclear matter and pure neutron
matter using realistic nucleon--nucleon potentials having non central tensor
and spin--orbit components, up to three times the empirical nuclear matter
saturation density, fm. The calculations are carried out
within the frameworks of the Brueckner--Bethe--Goldstone (BBG) and Correlated
Basis Functions (CBF) formalisms, in order to ascertain the accuracy of the
methods. The two hole--line approximation, with the continuous choice for the
single particle auxiliary potential, is adopted for the BBG approach, whereas
the variational Fermi Hypernetted Chain/Single Operator Chain theory, corrected
at the second order perturbative expansion level, is used in the CBF one. The
energies are then compared with the available Quantum and Variational Monte
Carlo results in neutron matter and with the BBG, up to the three hole--line
diagrams. For neutron matter and potentials without spin--orbit components all
methods, but perturbative CBF, are in reasonable agreement up to 3
. After the inclusion of the LS interactions, we still find agreement
around , whereas it is spoiled at larger densities. The spin--orbit
potential lowers the energy of neutron matter at by 3--4 MeV
per nucleon. In symmetric nuclear matter, the BBG and the variational results
are in agreement up to 1.5 . Beyond this density, and in
contrast with neutron matter, we find good agreement only for the potential
having spin--orbit components.Comment: 18 pages, 4 tables. Accepted in PL
Microscopic calculations of spin polarized neutron matter at finite temperature
The properties of spin polarized neutron matter are studied both at zero and
finite temperature within the framework of the Brueckner--Hartree--Fock
formalism, using the Argonne v18 nucleon-nucleon interaction. The free energy,
energy and entropy per particle are calculated for several values of the spin
polarization, densities and temperatures together with the magnetic
susceptibility of the system. The results show no indication of a ferromagnetic
transition at any density and temperature.Comment: 19 pages, 5 figure
Weather Radar Rainfall Summer Analysis of Irrigated vs Rainfed Nearby Areas
Màster de Meteorologia, Facultat de Física, Universitat de Barcelona, Curs: 2020-2021, Tutor: Joan BechThe objective of this work is to study rainfall characteristics (frequency, amount and type) in a semi-arid region in the Eastern Ebro basin (Iberian Peninsula). The region is included approximately in a 20 km per 30 km rectangle and is divided in two different areas, one irrigated with an artificial channel, and another one non-irrigated. The two areas may present a big difference of surface temperature in a short distance, particularly during midday hours of summer months due to high evapotranspiration contrasts. The study focusses in finding possible differences in rainfall characteristics between two areas. The methodology used is based on the analysis of radar reflectivity data, which is processed to determine the rainfall type, classified in convective and non-convective, a part of rain occurrence and amount. The work examined June, July and August data from years 2014 to 2020 analysing daily, monthly and total rain events distributions in both areas. The results show a big variability of the rainfall in the region depending on the year and as expected, an increase in convective rain in both areas during the afternoon. Although there is not a significant difference in the rainfall type nor in the convective rainfall rate between areas, there is a difference in the convective rain distribution along each area, being the rain in the irrigated part less homogenous than the non-irrigated part. This study has been performed in the framework of the Analysis of Precipitation Processes in the Eastern Ebro Subbasin project (WISE-PreP, RTI2018-098693-B-C32/AEI)
Anomalous specific heat jump in a two-component ultracold Fermi gas
The thermodynamic functions of a Fermi gas with spin population imbalance are
studied in the temperature-asymmetry plane in the BCS limit. The low
temperature domain is characterized by anomalous enhancement of the entropy and
the specific heat above their values in the unpaired state, decrease of the gap
and eventual unpairing phase transition as the temperature is lowered. The
unpairing phase transition induces a second jump in the specific heat, which
can be measured in calorimetric experiments. While the superfluid is unstable
against a supercurrent carrying state, it may sustain a metastable state if
cooled adiabatically down from the stable high-temperature domain. In the
latter domain the temperature dependence of the gap and related functions is
analogous to the predictions of the BCS theory.Comment: 4 pages, 3 figures. v2 includes a discussion of instabilities; v3:
final version to appear in PR
Hyperon effects on the properties of -stable neutron star matter
We present results from Brueckner-Hartree-Fock calculations for
-stable neutron star matter with nucleonic and hyperonic degrees of
freedom employing the most recent parametrizations of the baryon-baryon
interaction of the Nijmegen group. Only and are present up
to densities . The corresponding equations of state are then used
to compute properties of neutron stars such as masses and radii.Comment: 4 pages, contributed talk at HYP2000, Torino, 23-27 Oct. 200
Finite temperature effects on the antikaon optical potential
By solving the Bethe-Goldstone equation, we have obtained the
optical potential from the effective interaction in nuclear matter
at T=0. We have extended the model by incorporating finite temperature effects
in order to adapt our calculations to the experimental conditions in heavy-ion
collisions. In the rank of densities (), the finite temperature
optical potential shows a smooth behaviour if we compare it to the
T=0 outcome. Our model has also been applied to the study of the ratio between
and produced at GSI with around 70 MeV. Our results point at
the necessity of introducing an attractive optical potential.Comment: 7 pages, 4 figures. Contribution to the proceedings of Mesons & Light
Nuclei '01 (2-6th July, Prague
Correlations derived from Modern Nucleon-Nucleon Potentials
Various modern nucleon-nucleon (NN) potentials yield a very accurate fit to
the nucleon-nucleon scattering phase shifts. The differences between these
interactions in describing properties of nuclear matter are investigated.
Various contributions to the total energy are evaluated employing the Hellmann
- Feynman theorem. Special attention is paid to the two-nucleon correlation
functions derived from these interactions. Differences in the predictions of
the various interactions can be traced back to the inclusion of non-local
terms.Comment: 7 pages, 4 figures include
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