Rotating and counterrotating relativistic thin disks as sources of stationary electrovacuum spacetimes

A detailed study is presented of the counterrotating model (CRM) for electrovacuum stationary axially symmetric relativistic thin disks of infinite extension without radial stress, in the case when the eigenvalues of the energy-momentum tensor of the disk are real quantities, so that there is not heat flow. We find a general constraint over the counterrotating tangential velocities needed to cast the surface energy-momentum tensor of the disk as the superposition of two counterrotating charged dust fluids. We then show that, in some cases, this constraint can be satisfied if we take the two counterrotating tangential velocities as equal and opposite or by taking the two counterrotating streams as circulating along electro-geodesics. However, we show that, in general, it is not possible to take the two counterrotating fluids as circulating along electro-geodesics nor take the two counterrotating tangential velocities as equal and opposite. A simple family of models of counterrotating charged disks based on the Kerr-Newman solution are considered where we obtain some disks with a CRM well behaved. We also show that the disks constructed from the Kerr-Newman solution can be interpreted, for all the values of parameters, as a matter distribution with currents and purely azimuthal pressure without heat flow. The models are constructed using the well-known "displace, cut and reflect" method extended to solutions of vacuum Einstein-Maxwell equations. We obtain, in all the cases, counterrotating Kerr-Newman disks that are in agreement with all the energy conditions.Comment: 22 pages, 7 figures, Late

La proyección estereográfica

En este cursillo estudiaremos la proyección estereográfica. Dicha función es una proyección de la esfera, desde uno de sus puntos N, a un plano que toca a la esfera en un punto S diametralmente opuesto al punto N. Demostraremos que la proyección estereográfica preserva ángulos y envía circunferencias a rectas o a circunferencias. Analizaremos la relación entre la proyección estereográfica y la inversión respecto a una circunferencia. Finalmente definiremos el plano de Lobachevski y mostraremos cómo, mediante una proyección estereográfica especial, se puede obtener un modelo de este plano sobre un plano común conocido como el modelo de Poincaré para la geometría hiperbólica

The ε-approximated complete invariance property

[EN] In the present paper we introduce a generalization of the complete invariance property (CIP) for metric spaces, which we will call the εapproximated complete invariance property (ε-ACIP). For our goals, we will use the so called degree of nondensifiability (DND) which, roughly speaking, measures (in the specified sense) the distance from a bounded metric space to its class of Peano continua. Our main result relates the ε-ACIP with the DND and, in particular, proves that a densifiable metric space has the ε-ACIP for each ε > 0. Also, some essentials differences between the CIP and the ε-ACIP are shown.García, G. (2022). The ε-approximated complete invariance property. Applied General Topology. 23(2):453-462. https://doi.org/10.4995/agt.2022.1664145346223

Union Games: Technological Unemployment

Given a production economy, we define a trade union game by considering strategic behavior on factor supplies. We refer to the Nash equilibria of this game as trade union equilibria. First we analyze situations under which unemployment of factors are supported as trade union equilibria. The degree of unemployment depends on technological conditions. In this line, we suggest a source of unemployment which differs from the usual sources provided in the related literature. Then, we state a limit result which shows that when the market power of trade unions decreases the corresponding sequence of trade union equilibria converges to the walrasian equilibrium, that is, to full employment of factors.Trade Union Games, unemployment, walrasian equilibrium, manipulability.

El empoderamiento de las mujeres en las zonas rurales de Ghana

El empoderamiento de la mujer en las zonas rurales de GhanaGrado en Publicidad y Relaciones Pública

La onomástica de la conversión: señas de identidad y transformación antroponímica de los moriscos de Granada (1500-1569)

Las transformaciones padecidas por los musulmanes de Granada a raíz de la conversión masiva de 1499-1500 se reflejan en el cambio antroponímico inicial y su evolución durante el siglo XVI. En este estudio se evalúa la autenticidad de los nombres árabes en los documentos castellanos y se propone una metodología onomástica que abarca dos sistemas diversos (el árabe y el castellano) y que permite un cierto grado de sincretismo. La onomástica comparativa (sincrónica y diacrónica) desde la Edad Media hasta la Moderna, con muestras de otros colectivos permite calibrar el grado de aculturación de los moriscos y descubrir patrones de comportamiento cultural que resultan difícilmente discernibles por otros medios.The Muslims of Granada experienced a series of transformations due to the widespread conversions of 1499-1500 which is mirrored in the initial anthroponymic change and its subsequent evolution in the sixteenth century. This study assesses the authenticity of Arabic names in Castilian records and proposes an onomastic methodology that bridges two diverse systems (Arabic and Spanish) and manifests a certain degree of synchretism. A comparative onomastic study (both synchronic and diachronic) from medieval to early modern times, using various samples of other social groups allows us to gauge the degree of acculturation of the Moriscos and to discover patterns of cultural behaviour that would otherwise be difficult to discern.Este trabajo ha sido posible gracias a la financiación concedida en el marco del XIX Concurso de Ayudas a la Investigación para Temas Mudéjares 2007 del Centro de Estudios Mudéjares de Teruel