We consider a generalized statistical mechanics model for the creation process of cosmic rays which takes into account local temperature fluctuations. This model yields Tsallis statistics for the cosmic ray spectrum. It predicts an entropic index q given by q=11/9 at largest energies (equivalent to a spectral index of α=5/2), and an effective

In the first part of this article we show how observations of the chemical evolution of the Galaxy: G- and K-dwarf numbers as functions of metallicity, and abundances of the light elements, D, Li, Be and B, in both stars and the interstellar medium (ISM), lead to the conclusion that metal poor HI gas has been accreting to the Galactic disc during

There is considerable evidence that the circumnuclear regions of galaxies are intimately related to their host galaxies, most directly through their bars. There is also convincing evidence for relations between the properties of supermassive black holes in the nuclei of galaxies and those of their host galaxy. It is much less clear, however, how

Observations of quiescent filaments show very fine structures suggesting that they can be composed by smallscale threads or fibrils and, on the other hand, twodimensional, high-resolution observations have pointed out that individual fibrils or groups of fibrils may oscillate independently with their own periods. Using Cartesian geometry, Díaz et

In this work we consider the rich spectrum of fast MHD modes in low-beta, line-tied coronal loops (standing and leaky). One of the most important conclusions is that in a straight and homogeneous cylindrical flux tube there should be observational signatures of the excitation of higher order harmonics. Nevertheless, our results indicate that these

Bars drive the dynamical evolution of disk galaxies by redistributing mass and angular momentum, and they are ubiquitous in present-day spirals. Early studies of the Hubble Deep Field reported a dramatic decline in the rest-frame optical bar fraction f_opt to below 5% at redshifts z>0.7, implying that disks at these epochs are fundamentally