Structure of the inner crust of neutron stars: crystal lattice or disordered phase ?

We investigate the inner crust structure of neutron stars using the Skyrme-Hartree-Fock approach with the Coulomb interaction treated beyond the Wigner-Seitz approximation. Our results suggest that the shell effects associated with unbound neutrons play an important role and, in particular, lead to complicated phase transition pattern between various nuclear phases (as a function of the density). Namely, we show that the relative energies of different phases are rapidly oscillating functions of the neutron density. In the semiclassical approach this behavior is explained as an interference effect due to periodic orbits of similar lengths. We discuss also the dependence of the shell effects on pairing correlations.Comment: 20 pages, 5 figure

Properties of nuclei in the neutron star crust

In the present study we investigate the static properties of nuclei in the inner crust of neutron stars. Using the Hartree-Fock method in coordinate space, together with the semiclassical approximation, we examine the patterns of phase transitions.Comment: 6 pages, 1 figure, presented at the Nuclear Many-Body Problem 2001 - NATO Advanced Research Workshop, June 1-6, Brijuni, Croatia, 200

Nuclear tetrahedral configurations at spin zero

The possibility of the existence of stable tetrahedral deformations at spin zero is investigated using the Skyrme-HFBCS approach and the generator coordinate method (GCM). The study is limited to nuclei in which the tetrahedral mode has been predicted to be favored on the basis of non self-consistent models. Our results indicate that a clear identification of tetrahedral deformations is unlikely as they are strongly mixed with the axial octupole mode. However, the excitation energies related to the tetrahedral mode are systematically lower than those of the axial octupole mode in all the nuclei included in this study.Comment: 10 pages, 4 figure

Ultra directive antenna via transformation optics

Spatial coordinate transformation is used as a reliable tool to control electromagnetic fields. In this paper, we derive the permeability and permittivity tensors of a metamaterial able to transform an isotropically radiating source into a compact ultradirective antenna in the microwave domain. We show that the directivity of this antenna is competitive with regard to conventional directive antennas horn and reflector antennas, besides its dimensions are smaller. Numerical simulations using finite element method are performed to illustrate these properties. A reduction in the electromagnetic material parameters is also proposed for an easy fabrication of this antenna from existing materials. Following that, the design of the proposed antenna using a layered metamaterial is presented. The different layers are all composed of homogeneous and uniaxial anisotropic metamaterials, which can be obtained from simple metal-dielectric structures. When the radiating source is embedded in the layered metamaterial, a highly directive beam is radiated from the antenn

Is the American model Miss World? Choosing between the Anglo-Saxon model and a European-style alternative

In Lisbon, the European Union has set itself the goal to become the most competitive economy in the world in 2010 without harming social cohesion and the environment. The motivation for introducing this target is the substantially higher GDP per capita of US citizens. The difference in income is mainly a difference in the number of hours worked per employee. In terms of productivity per hour and employment per inhabitant, several European countries score equally well or even better than the United States, while at the same time they outperform the United States with a more equal distribution of income. The European social models are at least as interesting as the US model that is often considered a role model. In an empirical analysis for OECD countries, we aim to unravel 'the secret of success'. Our regression results show that income redistribution (through a social security system) does not necessarily lead to lower participation and higher unemployment, provided that countries supplement it with active labour market policies. Especially, spending on employment services like job-search assistance and vocational guidance, seems effective. Furthermore, the results suggest that generous unemployment benefits of short duration contribute to employment without widening the income distribution.

Beyond-mean-field study of the possible "bubble" structure of 34Si

Recent self-consistent mean-field calculations predict a substantial depletion of the proton density in the interior of 34Si. In the present study, we investigate how correlations beyond the mean field modify this finding. The framework of the calculation is a particle-number and angular-momentum projected Generator Coordinate Method based on Hartree-Fock-Bogoliubov+Lipkin-Nogami states with axial quadrupole deformation. The parametrization SLy4 of the Skyrme energy density functional is used together with a density-dependent pairing energy functional. For the first time, the generator coordinate method is applied to the calculation of charge and transition densities. The impact of pairing correlations, symmetry restorations and shape mixing on the density profile is analyzed step by step. All these effects significantly alter the radial density profile, and tend to bring it closer to a Fermi-type density distribution.Comment: 9 pages, 7 figure

Un modèle de l’offre de travail des bénéficiaires de l’aide sociale au Québec

Cet article présente la stratégie de recherche d'un projet qui vise à analyser le comportement des bénéficiaires de l'aide sociale concernant leurs activités de travail et de prospection d'emploi, afin de mieux connaître les déterminants de leurs plans d'offre de travailThis paper presents a labor supply model of the low-incomes individuals which will be applied to data collected by a survey of the population on welfare in Québec during 1976. The model specifies the variables which determine the subjective wage rate as an indicator of the incentive to work. This equation of the subjective wage rate is the structural form of the model while a labor supply equation and a market wage rate equation constitute the reduced form. The amount of labor supplied is thus a function of the cost of job search, the length of the search period, the net wage rate, the individual amount of rationing in the labor market, autonomous income etc.. The exact econometric specification of the model will be presented when the results of the estimation will be communicated