Collisional excitation of neutral hydrogen atoms can significantly increase the intensity of Balmer lines with respect to pure recombination. If this effect is not taken into account, the abundance analysis of these objects returns biased values, and the bias may be significant if accuracies better than a few percent are required. The most affected

We classify 46 broad band surface-brightness profiles in the visible from a sample of nearby early-type unbarred galaxies imaged at the ING (La Palma) and in the SDSS. A key result is that the fraction of these galaxies showing truncations in their outer disks is relatively small (of order 10%). The largest single category of galaxies show what tet

We examine closely the solar center-to-limb variation of continua and lines and compare observations with predictions from both a three-dimensional (3D) hydrodynamic simulation of the solar surface (provided by M. Asplund and collaborators) and one-dimensional (1D) model atmospheres. Intensities from the 3D time series are derived by means of the

Boxy/peanut bulges in disk galaxies have been associated with stellar bars. We analyze their properties in a large sample of N-body simulations, using different methods to measure their strength, shape, and possible asymmetry, and then to intercompare the results. Some of these methods can be applied to both simulations and observations. In

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In this article we describe a series of projects designed to supply families in rural Bolivia with heat for their cooking needs using simple technology to derive biogas from a mixture of animal manure and water. The novelty is that the adaptation of the anaerobic fermentation process to the climatic conditions at 4000 m above sea level has, for the