The behavior and properties of neutrinos in non-uniform nuclear matter, surrounded by electrons and other neutrinos are studied. The nuclear matter itself is modeled by the non-linear Walecka model, where the so-called nuclear pasta phase is described using the Thomas-Fermi approximation, solved in a Wigner-Seitz cell. We obtain the total cross-section and mean-free path for the neutrinos, taking into account scattering and neutrino absorption, and compare the final results for two known kind of model parametrizations: one in which non-linear effects in the strong sector are explicitly written in the model Lagrangian and another one in which the coupling constants are density dependent. The solution for this problem is important for the understanding of neutrino diffusion in a newly born neutron star after a supernova explosion. PACS number(s): 24.10. Jv,25.30.Pt,21.65.Mn
Pairing effects in non-uniform nuclear matter, surrounded by electrons, are studied in the protoneutron star early stage and in other conditions. The so-called nuclear pasta phases at sub saturation densities are solved in a Wigner-Seitz cell, within the Thomas-Fermi approximation. The solution of this problem is important for the understanding of the physics of a newly born neutron star after a supernova explosion. It is shown that the pasta phase is more stable than uniform nuclear matter on some conditions and the pairing force relevance is studied in the determination of these stable phases.
We perform extended Thomas–Fermi calculations in the Wigner–Seitz cell below and above neutron drip with realistic functionals. The resulting energy density is decomposed as a sum of bulk terms and a surface term, and a compressible liquid drop analytical formula is used to fit the surface tension. The effect of curvature terms and neutron skin is studied in detail. A very good reproduction of the microscopic data is obtained using an expression that depends only on the mass and charge of the cluster, showing that the in-medium modifications of the nuclear energy in the presence of an external neutron gas can be effectively accounted for in the isospin dependence of the surface tension. In this first application, aimed at establishing the fitting protocol, we concentrate on the Sly4 energy functional, but the study can be easily generalized to different functionals, and the resulting parametrizations can be used for direct applications in pasta calculations in neutron star crusts and supernova matter.
Este trabalho aborda uma investigação acerca da resolução de problemas no Ensino de Física no âmbito da disciplina de Estágio Supervisionado, realizado em uma turma do segundo ano do ensino médio, tendo como objetivo principal analisar o engajamento dos alunos em práticas de resolução de problemas. Os fracassos observados em avaliações baseadas em resolução de problemas demonstram a necessidade de se trabalhar este assunto em sala de aula por parte do professor e de toda a escola. Estudantes, sem uma preparação para tal, são incapazes de resolver problemas de lápis e papel e problemas abertos em física. A resolução de problemas abertos vai ao encontro de posições filosóficas que defendem uma postura mais ativa do aluno durante o processo de ensino-aprendizagem. Entre outros benefícios, a resolução de problemas contribui para o aprendizado da teoria, para dinamizar a aula e para formar cidadãos mais conscientes do mundo ao seu redor e do impacto de suas ações nele, inclusive fora de sala de aula. Conclui-se então que a resolução de problemas, principalmente os abertos, é uma ferramenta útil em vários aspectos no processo de ensino-aprendizagem, além de ser de baixo custo material, ou seja, não demanda a presença de grandes recursos, podendo ser trabalhada em praticamente qualquer escola.
Relativistic models for the many-body system may have applications in nuclear astrophysics, as neutron stars, and also in finite nuclei. In this paper we are interested in analyzing the importance of neutrinos and its interactions within a dense nuclear matter through such a model. We calculate the energy per particle for a many-body system using the mean-field approach, where the meson fields are replaced by their expectation values . The model parameters can be adjusted to agree with results for nuclear matter and astrophysical observations. We start with a Lagrangian density including nucleons, mesons, electrons and neutrinos. After solving the corresponding equations, we use the energy-momentum tensor to calculate the energy density and pressure, as well as neutrino cross sections. Values for the coupling parameters in the model are taken from previous work.
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