Magnetized, Relativistic Jets

Extragalactic relativistic jets are composed by charged particles and magnetic fields, as inferred from the synchrotron emission that we receive from them. The Larmor radii of the particles propagating along the magnetic field are much smaller than the scales of the problem, providing the necessary coherence to the system to treat is as a flow. We can thus study them using relativistic magnetohydrodynamics. As a first step, we have studied the structure of steady-state configurations of jets by using numerical simulations. We have used a helical field configuration and have changed different relevant parameters that control the way in which the energy flux is distributed in jets (namely, the proportion of the energy flux carried by internal, kinetic or magnetic energy). Our results show significant differences among the different kinds of jets. Finally, we also report on results based on synthetic maps of our simulated jets.Comment: Submitted for publication in Proceedings of Science, as contribution to the proceedings of the XII Multifrequency Behaviour of High Energy Cosmic Sources Workshop, held in Palermo, 12-17 June 201

La industria de la nieve en las montañas alicantinas

En número dedicado a: La provincia de Alicant

On the convexity of Relativistic Ideal Magnetohydrodynamics

We analyze the influence of the magnetic field in the convexity properties of the relativistic magnetohydrodynamics system of equations. To this purpose we use the approach of Lax, based on the analysis of the linearly degenerate/genuinely non-linear nature of the characteristic fields. Degenerate and non-degenerate states are discussed separately and the non-relativistic, unmagnetized limits are properly recovered. The characteristic fields corresponding to the material and Alfv\'en waves are linearly degenerate and, then, not affected by the convexity issue. The analysis of the characteristic fields associated with the magnetosonic waves reveals, however, a dependence of the convexity condition on the magnetic field. The result is expressed in the form of a generalized fundamental derivative written as the sum of two terms. The first one is the generalized fundamental derivative in the case of purely hydrodynamical (relativistic) flow. The second one contains the effects of the magnetic field. The analysis of this term shows that it is always positive leading to the remarkable result that the presence of a magnetic field in the fluid reduces the domain of thermodynamical states for which the EOS is non-convex.Comment: 14 pages. Submitted to Classical and Quantum Gravit

La disyuntiva entre pedagogía formalista y personalista

La educación digna de este nombre es de calidad. Ello equivale a decir que sea personalizada y se desenvuelva en libertad. En cuanto que personal procederá desde dentro y se cimentará en las virtudes. El ejemplo y generosidad de los padres garantizan el proceso. Sin embargo, de la mano de los organismos nacionales e internacionales, se ha extendido el formalismo pedagógico. Se sustenta en un objetivo abstracto que lo fía todo en el pragmatismo y las consignas ideológicas. Esta opción genera pasividad y malestar social. La familia marca la buena dirección para que cada niño se forme y desarrolle plenamente (voluntad e inteligencia)