Momentum, Density, and Isospin dependence of the Symmetric and Asymmetric Nuclear Matter Properties

Properties of symmetric and asymmetric nuclear matter have been investigated in the relativistic Dirac-Brueckner-Hartree-Fock approach based on projection techniques using the Bonn A potential. The momentum, density, and isospin dependence of the optical potentials and nucleon effective masses are studied. It turns out that the isovector optical potential depends sensitively on density and momentum, but is almost insensitive to the isospin asymmetry. Furthermore, the Dirac mass $m^*_D$ and the nonrelativistic mass $m^*_{NR}$ which parametrizes the energy dependence of the single particle spectrum, are both determined from relativistic Dirac-Brueckner-Hartree-Fock calculations. The nonrelativistic mass shows a characteristic peak structure at momenta slightly above the Fermi momentum \kf. The relativistic Dirac mass shows a proton-neutron mass splitting of $m^*_{D,n} <m^*_{D,p}$ in isospin asymmetric nuclear matter. However, the nonrelativistic mass has a reversed mass splitting $m^*_{NR,n} >m^*_{NR,p}$ which is in agreement with the results from nonrelativistic calculations.Comment: 25 pages, 12 figures, to appear in Physical Review

Spinodal Instabilities in Asymmetric Nuclear Matter Based on Realistic NNNN Interactions

A density dependent relativistic mean-field model is determined to reproduce the components of the nucleon self-energy at low densities. This model is used to investigate spinodal instabilities in isospin asymmetric nuclear matter at finite temperatures. The inhomogeneous density distributions in the spinodal region are investigated through calculations in a cubic Wigner-Seitz cell. Compared to results obtained in phenomenological calculations the spinodal region is large, i.e. the spinodal region at zero temperature can reach densities above 0.12 fm$^{-3}$. The predicted spinodal region is concentrated around isospin symmetric nuclear matter and the critical temperature is considerably lower than in the previous microscopic based investigation within a non-relativistic Brueckner-Hartree-Fock approach.Comment: 11 pages, 7 figure

Alcohol outlets near schools in a midsize Romanian city : prevalence and characteristics

Objective: alcohol availability is one of the strongest predictors of adolescent alcohol use, and subsequent harm. Alcohol outlets near schools are an important indicator of three types of availability related to adolescent alcohol use; physical (number), economic (price), and legal (compliance with age limits).\ud \ud Method: two teams with trained students (16 and 17 years old) visited all 37 schools in a 200,000 inhabitant Romanian city (Pitesti). On the spot all alcohol outlets were visited and data was collected on outlet characteristics and visitors. Also, by conducting mystery shopping purchase attempts by the researchers, compliance on the age limits for alcohol sales was tested.\ud \ud Results: a total of 40 outlets were found within a 250 meter distance around 23 schools. Alcohol turns out to be cheap, and commercial alcohol brand signs are dominantly visible. With respect to compliance with the 18-year-old Romanian age limit for alcohol sales, only eight (20%) outlets refused to sell alcohol to under aged decoy customers.\ud \ud Conclusion: adolescent alcohol availability is high on the physical, economic and legal aspect. Pitesti is the first city in\ud Romania where an international alcohol prevention project has started to reduce alcohol related consequences. This project\ud involves all relevant stakeholders, and the first new legislation on this subject had been implemented

Dirac-Brueckner-Hartree-Fock calculations for isospin asymmetric nuclear matter based on improved approximation schemes

We present Dirac-Brueckner-Hartree-Fock calculations for isospin asymmetric nuclear matter which are based on improved approximations schemes. The potential matrix elements have been adapted for isospin asymmetric nuclear matter in order to account for the proton-neutron mass splitting in a more consistent way. The proton properties are particularly sensitive to this adaption and its consequences, whereas the neutron properties remains almost unaffected in neutron rich matter. Although at present full Brueckner calculations are still too complex to apply to finite nuclei, these relativistic Brueckner results can be used as a guidance to construct a density dependent relativistic mean field theory, which can be applied to finite nuclei. It is found that an accurate reproduction of the Dirac-Brueckner-Hartree-Fock equation of state requires a renormalization of these coupling functions.Comment: 34 pages, 9 figures, submitted to Eur. Phys. J.

Model independent study of the Dirac structure of the nucleon-nucleon interaction

Relativistic and non-relativistic modern nucleon-nucleon potentials are mapped on a relativistic operator basis using projection techniques. This allows to compare the various potentials at the level of covariant amplitudes were a remarkable agreement is found. In nuclear matter large scalar and vector mean fields of several hundred MeV magnitude are generated at tree level. This is found to be a model independent feature of the nucleon-nucleon interaction.Comment: 5 pages, 2 figures, results for V_lowk added, to appear in PR