Torsional oscillations of magnetized neutron stars with mixed poloidal-toroidal fields

The quasiperiodic oscillations found in the three giant flares of soft gamma-ray repeaters observed to date have been interpreted as crustal oscillations caused by a starquake following a dramatic rearrangement of the stellar magnetic field. Motivated by these observations, we study the influence of the magnetic field geometry in the frequencies of the torsional oscillations of magnetized neutron stars. We use realistic tabulated equations of state for the core and crust of the stars and model their magnetic field as a dipole plus a toroidal component, using the relativistic Grad-Shafranov equation. The frequencies of the torsional modes are obtained by the numerical solution of the eigenvalue problem posed by the linear perturbation equations in the Cowling approximation. Our results show how the asteroseismology of these stars becomes complicated by the degeneracy in the frequencies due to the large relevant parameter space. However, we are able to propose a testable scenario in which the rearrangement of the magnetic field causes an evolution in the frequencies. Finally, we show that there is a magnetic field configuration that maximizes the energy in the perturbation at linear order, which could be related to the trigger of the giant flare.Comment: 13 pages, 11 figures, version accepted for publication in PR

Poverty, Inequality and Social Policies in Brazil, 1995-2009

Since the mid-1990s, Brazil has undergone extensive reforms that have finally reversed the dismaying economic performance of the 1980s. In particular, poverty and inequality indicators have improved dramatically, especially since the late-2000s. This paper provides an overview of such recent trends and discusses the role played by four major government interventions: public education, the minimum wage law, Social Security pensions and Social Assistance transfers. Additionally, available data sets and methods for policy evaluation are also discussed. (?)Poverty, Inequality and Social Policies in Brazil, 1995-2009

Social Policies and the Fall in Inequality in Brazil: Achievements and Challenges

By the end of the first decade of the 21st century, the most usual international depiction of Brazil is that of a burgeoning, upcoming country. Although in many ways frankly exaggerated, this marks a stark contrast with a not-so-distant past. This turnaround has had a lot to do with favourable international circumstances, but it also owes a lot to extensive reforms that made possible something that was almost unprecedented in Brazil: pro-poor growth. (?)Social Policies and the Fall in Inequality in Brazil: Achievements and Challenges

Fundamental oscillation modes of neutron stars: validity of universal relations

We study the $f$-mode frequencies and damping times of nonrotating neutron stars (NS) in general relativity (GR) by solving the linearized perturbation equations, with the aim to establish "universal" relations that depend only weakly on the equations of state (EOS). Using a more comprehensive set of EOSs, we re-examine some proposed linearizations that describe the $f$-mode parameters in terms of mass and radius of the neutron star (NS), and we test a more recent proposal for expressing the $f$-mode parameters as quadratic functions of the effective compactness. Our extensive results for each equation of state considered allow us to study the accuracy of each proposal. In particular, we find that the damping time deviates quite considerably from the proposed linearization. We introduce a new universal relation for the product of the $f$-mode frequency and damping time as a function of the (ordinary) compactness, which proved to be more accurate. The relations using the effective compactness on the other hand also fit our data accurately. Our results show that the maximum oscillation frequency depends strongly on the EOS, such that the measurement of a high oscillation frequency would rule out several EOSs. Lastly, we compare the exact mode frequencies to those obtained in the Cowling approximation, and also to results obtained with a nonlinear evolution code, validating the implementations of the different approaches.Comment: 10 pages, 8 figures, v2: final version accepted for publication in Phys.Rev.