Gravitational waves : a 100-year tool applied to the dark energy problem

Recent observations from type Ia Supernovae and from cosmic microwave background (CMB) anisotropies have revealed that most of the matter of the Universe interacts in a repulsive manner, composing the so-called dark energy constituent of the Universe. Determining the properties of dark energy is one of the most important tasks of modern cosmology and this is the main motivation for this work. The analysis of cosmic gravitational waves (GW) represents, besides the CMB temperature and polarization anisotropies, an additional approach in the determination of parameters that may constrain the dark energy models and their consistence. In recent work, a generalized Chaplygin gas model was considered in a flat universe and the corresponding spectrum of gravitational waves was obtained. In the present work we have added a massless gas component to that model and the new spectrum has been compared to the previous one. The Chaplygin gas is also used to simulate a L-CDM model by means of a particular combination of parameters so that the Chaplygin gas and the L-CDM models can be easily distinguished in the theoretical scenarios here established. We find that the models are strongly degenerated in the range of frequencies studied. This degeneracy is in part expected since the models must converge to each other when some particular combinations of parameters are considered.

Álcool e direção : uma questão na agenda política brasileira

Analisar como o problema do álcool e direção foi incorporado à agenda política brasileira é o objetivo deste trabalho. Entre as décadas de 1980 e 1990, as taxas dos acidentes de trânsito correspondiam a quase metade dos óbitos por causas externas, com tendências crescentes. Foi nas últimas duas décadas do século XX, que os acidentes de trânsito foram definidos como problema de saúde pública e, dentro da discussão dos acidentes, violência e óbitos por causas externas, a combinação álcool e direção foi configurada como um problema que requer políticas públicas.