3,365 research outputs found
The nuclear symmetry energy and other isovector observables from the point of view of nuclear structure
In this contribution, we review some works related with the extraction of the
symmetry energy parameters from isovector nuclear excitations, like the giant
resonances. Then, we move to the general issue of how to assess whether
correlations between a parameter of the nuclear equation of state and a nuclear
observable are robust or not. To this aim, we introduce the covariance analysis
and we discuss some counter-intuitive, yet enlightening, results from it.Comment: To be published in the proceedings of the 2014 Zakopane Conference on
Nuclear Physics (Acta Physica Polonica B
Neutron skin of 208Pb, nuclear symmetry energy, and the parity radius experiment
A precise determination of the neutron skin thickness of a heavy nucleus sets
a basic constraint on the nuclear symmetry energy (the neutron skin thickness
is the difference of the neutron and proton rms radii of the nucleus). The
parity radius experiment (PREX) may achieve it by electroweak parity-violating
electron scattering (PVES) on 208Pb. We investigate PVES in nuclear mean field
approach to allow the accurate extraction of the neutron skin thickness of
208Pb from the parity-violating asymmetry probed in the experiment. We
demonstrate a high linear correlation between the parity-violating asymmetry
and the neutron skin thickness in successful mean field forces as the best
means to constrain the neutron skin of 208Pb from PREX, without assumptions on
the neutron density shape. Continuation of the experiment with higher precision
in the parity-violating asymmetry is motivated since the present method can
support it to constrain the density slope of the nuclear symmetry energy to new
accuracy.Comment: 4 pages, 3 figures, some changes in text and references, version to
appear in Phys. Rev. Let
Spin injection from EuS/Co multilayers into GaAs detected by polarized electroluminescence
We report on the successful spin injection from EuS/Co multilayers into (100) GaAs at low temperatures. The spin injection was verified by means of polarized electroluminescence (EL) emitted from AlGaAs/GaAs-based spin-light-emitting diodes in zero external magnetic field. Spin-polarized electrons were injected from prototype EuS/Co spin injector multilayers. The use of semiconducting and ferromagnetic EuS circumvents the impedance mismatch. The EL was measured in side emission with and without an external magnetic field. A circular polarization of 5% at 8 K and 0 T was observed. In view of the rather rough interface between the GaAs substrate and first EuS layer, improvement of the interface quality is expected to considerably enhance the injected electron spin polarization
Imperfect Imitation Can Enhance Cooperation
The promotion of cooperation on spatial lattices is an important issue in
evolutionary game theory. This effect clearly depends on the update rule: it
diminishes with stochastic imitative rules whereas it increases with
unconditional imitation. To study the transition between both regimes, we
propose a new evolutionary rule, which stochastically combines unconditional
imitation with another imitative rule. We find that, surprinsingly, in many
social dilemmas this rule yields higher cooperative levels than any of the two
original ones. This nontrivial effect occurs because the basic rules induce a
separation of timescales in the microscopic processes at cluster interfaces.
The result is robust in the space of 2x2 symmetric games, on regular lattices
and on scale-free networks.Comment: 4 pages, 4 figure
Nuclear equation of state from ground and collective excited state properties of nuclei
This contribution reviews the present status on the available constraints to the nuclear equation of state (EoS) around saturation density from nuclear structure calculations on ground and collective excited state properties of atomic nuclei. It concentrates on predictions based on self-consistent mean-field calculations, which can be considered as an approximate realization of an exact energy density functional (EDF). EDFs are derived from effective interactions commonly fitted to nuclear masses, charge radii and, in many cases, also to pseudo-data such as nuclear matter properties. Although in a model dependent way, EDFs constitute nowadays a unique tool to reliably and consistently access bulk ground state and collective excited state properties of atomic nuclei along the nuclear chart as well as the EoS. For comparison, some emphasis is also given to the results obtained with the so called ab initio approaches that aim at describing the nuclear EoS based on interactions fitted to few-body data only. Bridging the existent gap between these two frameworks will be essential since it may allow to improve our understanding on the diverse phenomenology observed in nuclei. Examples on observations from astrophysical objects and processes sensitive to the nuclear EoS are also briefly discussed. As the main conclusion, the isospin dependence of the nuclear EoS around saturation density and, to a lesser extent, the nuclear matter incompressibility remain to be accurately determined. Experimental and theoretical efforts in finding and measuring observables specially sensitive to the EoS properties are of paramount importance, not only for low-energy nuclear physics but also for nuclear astrophysics applications
Mixed-mode impedance and reflection coefficient of two-port devices
From the point of view of mixed-mode scattering parameters, Smm, a two-port device can be excited using different driving conditions. Each condition leads to a particular set of input reflection and input impedance coefficient definitions that should be carefully applied depending on the type of excitation and symmetry of the two-port device. Therefore, the aim of this paper is to explain the general analytic procedure for the evaluation of such reflection and impedance coefficients in terms of mixed-mode scattering parameters. Moreover, the driving of a two-port device as a one-port device is explained as a particular case of a two-port mixed-mode excitation using a given set of mixed-mode loads. The theory is applied to the evaluation of the quality factor, Q, of symmetrical and non- symmetrical inductors.Ministerio de Innovación y Ciencia TEC2010-14825/MIC, TEC2010-21484Junta de Andalucía TIC-253
Predictions of super-exotic heavy mesons from interactions
We make a theoretical study of the three-body system composed of to look for possible bound states, which could be
associated to mesonic resonances of very exotic nature, containing open strange
and double-bottom flavours. The three-body interaction is evaluated by using
the fixed center approach to the Faddeev equations where the is bound forming an state, as it was found in previous
works, and the third particle, the , of much smaller mass,
interacts with the components of the cluster. We obtain bound states for all
the channels considered: spin , 1 and 2, all of them with isospin
and negative parity.Comment: 9 pages, 5 figure
TESTING A COMBINED MULTISPECTRAL-MULTITEMPORAL APPROACH FOR GETTING CLOUDLESS IMAGERY FOR SENTINEL-2
Abstract. Earth observation and land cover monitoring are among major applications for satellite data. However, the use of primary satellite information is often limited by clouds, cloud shadows, and haze, which generally contaminate optical imagery. For purposes of hazard assessment, for instance, such as flooding, drought, or seismic events, the availability of uncontaminated optical data is required. Different approaches exist for masking and replacing cloud/haze related contamination. However, most common algorithms take advantage by employing thermal data. Hence, we tested an algorithm suitable for optical imagery only. The approach combines a multispectral-multitemporal strategy to retrieve daytime cloudless and shadow-free imagery. While the approach has been explored for Landsat information, namely Landsat 5 TM and Landsat 8 OLI, here we aim at testing the suitability of the method for Sentinel-2 Multi-Spectral Instrument. A multitemporal stack, for the same image scene, is employed to retrieve a composite uncontaminated image over a temporal period of few months. Besides, in order to emphasize the effectiveness of optical imagery for monitoring post-disaster events, two temporal stages have been processed, before and after a critical seismic event occurred in Lombok Island, Indonesia, in summer 2018. The approach relies on a clouds and cloud shadows masking algorithm, based on spectral features, and a data reconstruction phase based on automatic selection of the most suitable pixels from a multitemporal stack. Results have been tested with uncontaminated image samples for the same scene. High accuracy is achieved
Electric dipole polarizability and the neutron skin
The recent high-resolution measurement of the electric dipole (E1)
polarizability (alphad) in 208Pb [Phys. Rev. Lett. 107, 062502 (2011)] provides
a unique constraint on the neutron-skin thickness of this nucleus. The
neutron-skin thickness (rskin) of 208Pb is a quantity of critical importance
for our understanding of a variety of nuclear and astrophysical phenomena. To
assess the model dependence of the correlation between alphad and rskin, we
carry out systematic calculations for 208Pb, 132Sn, and 48Ca based on the
nuclear density functional theory (DFT) using both non-relativistic and
relativistic energy density functionals (EDFs). Our analysis indicates that
whereas individual models exhibit a linear dependence between alphad and rskin,
this correlation is not universal when one combines predictions from a host of
different models. By averaging over these model predictions, we provide
estimates with associated systematic errors for rskin and alphad for the nuclei
under consideration. We conclude that precise measurements of rskin in both
48Ca and 208Pb---combined with the recent measurement of alphad---should
significantly constrain the isovector sector of the nuclear energy density
functional.Comment: Manuscript contains 5 pages, 2 figures, and 1 table. Submitted to
Physical Review Letter
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