Capture of field stars by giant interstellar clouds: the formation of moving stellar groups

In the solar neighbourhood, there are moving groups of stars with similar ages and others of stars with heterogeneous ages as the field stars. To explain these facts, we have constructed a simple model of three phases. Phase A: a giant interstellar cloud is uniformly accelerated (or decelerated) with respect to the field stars during a relatively short period of time (10 Myr) and the cloud's mass is uniformly increased; phase B: the acceleration (or deceleration) and mass accretion of the cloud cease. The star formation spreads throughout the cloud, giving origin to stellar groups of similar ages; and phase C: the cloud loses all its gaseous component at a constant rate and in parallel is uniformly decelerated (or accelerated) until reaching the initial velocity of phase A (case 1) or the velocity of the gas cloud remains constant (case 2). Both cases give equivalent results. The system equations for the star motions governed by a time-dependent gravitational potential of the giant cloud and referred to a coordinate system co-moving with the cloud have been solved analytically. We have assumed a homogeneous spheroidal cloud of fixed semi-major axis a=300 pc and of an initial density of 7 at cm^{-3}, with a density increment of 100 per cent and a cloud's velocity variation of 30 km s^{-1}, from the beginning to the end of Phase A. The result is that about 4 per cent of the field stars that are passing within the volume of the cloud at the beginning of phase A is captured. The Sun itself could have been captured by the same cloud that originated the moving groups of the solar neighbourhood.Comment: 13 pages, 15 figure

La pluralitat dels informatius en les televisions públiques i la responsabilitat social corporativa (RSC) amb atenció al cas de RTVV

En l'article abordem les teories de la responsabilitat social corporativa (rsC) i altres de similars, comunes en el camp econòmic, i analitzem l'efectivitat del seu ús respecte a la pluralitat dels serveis informatius en els mitjans audiovisuals, especialment els públics. Concretament, comprovem l'efectivitat dels seus postulats en l'última etapa agònica de Canal 9 rTVV, sota la direcció de rosa Vidal, i com poden afectar el futur de la televisió autonòmica en aquesta fase de tabula rasa en què ens trobem avui. el futur de les televisions públiques no és només qüestió de proteccions jurídiques i organismes reguladors. la rsC pot esdevenir un factor determinant en el disseny del nou model audiovisual que s'aborda políticament. In this article we deal with the theories of corporate social responsibility (CSR) and similar ones, which are common in the economic field, and we analyze their efficacy on the plurality of TV news programs, especially the public ones. We check the usefulness of their postulates in what was the final stage of RTVV Canal 9, under the direction of Rosa Vidal, and consider how they can affect the future of the regional television in Valencia in the tabula rasa phase we are in today. The future of the public television is not only a matter of legal protections and regulatory bodies. CSR can become a decisive element in the design of the new audiovisual model which politicians are now addressing

La evolución de la base legal de radiotelevisión valenciana. Perspectivas de futuro

En el artículo hacemos un recorrido por la historia jurídica de RTVV. Repasaremos las leyes que rigieron este servicio audiovisual autonómico y si se han cumplido o no. El entramado legal es la base del funcionamiento de un medio de comunicación público ahora enmudecido. El abrupto cierre de la radiotelevisión autonómica deja como herencia un lío que hay que aclarar en primer lugar. Los legisladores tienen ahora por delante la tarea de volver a poner en marcha el servicio público, y, además, de hacerlo con la suficiente responsabilidad para que los viejos errores no vuelvan a cometerse

Las autoridades de regulación audiovisual en España: panorámica y perspectivas del control de la pluralidad

Las autoridades de regulación audiovisual son un instrumento de control, entre otras cosas, de la pluralidad informativa de las televisiones públicas. Así lo reconocen diversas leyes a nivel comunitario y estatal. En España, la asunción de la autoridad en materia audiovisual por parte de la Comisión Nacional de los Mercados y la Competencia (CNMC), nos ha incorporado tarde y mal al entorno europeo, donde son habituales estos consejos. También en las diferentes Comunidades Autónomas, hay un déficit regulatorio que hace que tan sólo Catalunya y Andalucía estén dotadas de este instrumento. En el artículo estudiaremos el 'estado del arte' sobre la cuestión, para poder valorar nuestro entorno, con especial atención al caso singular en la Comunitat Valenciana, que se enfrenta a una situación de tabula rasa en materia audiovisual. A pesar de que tanto el Estatut d'Autonomia como la ley audiovisual obligaban a la creación del Consell Audiovisual Valencià desde hace nueve años, el antiguo gobierno de la Generalitat, en consonancia con la política del PP en toda España, bloqueó la iniciativa. Los condicionantes políticos después de las convocatorias electorales de los años 2015 y 2016 influirán sin duda en el panorama futuro respecto a estas herramientas de control

Destellos en el túnel: la apertura informativa en la época de NOU según los protagonistas

Canal 9 -o Nou, como se llamó en su última etapa- con su carácter ejemplarizante para el resto de autonómicas, se convierte en el objeto de estudio perfecto para los investigadores en comunicación. El trabajo se centra en la última etapa de RTVV, bajo la influencia de un nuevo estatuto legal, que dotaba a la televisión de herramientas presuntamente facilitadoras de la pluralidad en los informativos. Mediante un análisis cualitativo basado en entrevistas semiestructuradas a un panel de expertos, intentamos averiguar si se produjo en ese tiempo un cambio apreciable en la redacción de Canal 9, combinado con un cambio de talante en la gestión de la empresa. La conclusión, con los matices que desarrollamos en el texto, es que sí que se produjo una apertura en esa fase, que desgraciadamente fue abortada por el cierre precipitado. La eliminación de la emisora autonómica provocó un efecto destructivo en cadena en el sistema audiovisual valenciano que aún no se ha superado

Els informatius de Canal 9 en l’etapa sota la direcció de Rosa Vidal. Un estudi mitjançant la tècnica Delphi

In the last stage of RTVV before closing, with Rosa Vidal as general director of the broadcasting station (April-November 2013), according to some authors there was a not expected increasing of plurality never seen in the last twenty years. This attempt to recover the basis of the service, which should characterize public television –journalistic independenceand the fact of providing an informative narration of quality– lasted only seven months, just before the abrupt end of the broadcasting ordered on November 5th 2013. The intention of managers was to recover the prestige of the news programmes, and to restore transparency and governance in the channel. And through them, to get the rising of the confidence, and the television audience buried in a brutal debt and in a continuous spiral of corruption in recent years. The approach to this last stage is done using Delphi type polls, conducted by a selected panel of experts. The group that focuses the analysis consists of managers, supervisors that performed their task from the Board of governors, and representatives of workers

Capture of field stars by giant interstellar clouds: the formation of moving stellar groups

In the solar neighbourhood, there are moving groups of stars with similar ages and others of stars with heterogeneous ages as the field stars. To explain these facts, we have constructed a simple model of three phases. Phase A: a giant interstellar cloud is uniformly accelerated (or decelerated) with respect to the field stars during a relatively short period of time (10 Myr) and the cloud's mass is uniformly increased. As a result, a number of passing field stars is gravitationally captured by the cloud at the end of this phase; phase B: the acceleration (or deceleration) and mass accretion of the cloud cease. The star formation spreads throughout the cloud, giving origin to stellar groups of similar ages; and phase C: the cloud loses all its gaseous component at a constant rate and in parallel is uniformly decelerated (or accelerated) until reaching the initial velocity of phase A (case 1) or the velocity of the gas cloud remains constant (case 2). Both cases give equivalent results. The system equations for the star motions governed by a time-dependent gravitational potential of the giant cloud and referred to a coordinate system comoving with the cloud have been solved analytically. We have assumed a homogeneous spheroidal cloud of fixed semimajor axis a = 300 pc and of an initial density of 7 atoms cm-3, with a density increment of 100 per cent and a cloud's velocity variation of 30 km s-1, from the beginning to the end of phase A. The result is that about 4 per cent of the field stars that are passing within the volume of the cloud at the beginning of phase A are captured. The Sun itself could have been captured by the same cloud that originated the moving groups of the solar neighbourhood.Facultad de Ciencias Astronómicas y Geofísica

The propagation of the shock wave from a strong explosion in a plane-parallel stratified medium: The Kompaneets approximation

Context. Using certain simplifications, Kompaneets derived a partial differential equation that states the local geometrical and kinematical conditions that each surface element of a shock wave, created by a point blast in a stratified gaseous medium, must satisfy. Kompaneets could solve his equation analytically for the case of a wave propagating in an exponentially stratified medium, obtaining the form of the shock front at progressive evolutionary stages. Complete analytical solutions of the Kompaneets equation for shock wave motion in further plane-parallel stratified media were not found, except for radially stratified media. Aims. We aim to analytically solve the Kompaneets equation for the motion of a shock wave in different plane-parallel stratified media that can reflect a wide variety of astrophysical contexts. We were particularly interested in solving the Kompaneets equation for a strong explosion in the interstellar medium of the Galactic disk, in which, due to intense winds and explosions of stars, gigantic gaseous structures known as superbubbles and supershells are formed. Methods. Using the Kompaneets approximation, we derived a pair of equations that we call adapted Kompaneets equations, that govern the propagation of a shock wave in a stratified medium and that permit us to obtain solutions in parametric form. The solutions provided by the system of adapted Kompaneets equations are equivalent to those of the Kompaneets equation. We solved the adapted Kompaneets equations for shock wave propagation in a generic stratified medium by means of a power-series method. Results. Using the series solution for a shock wave in a generic medium, we obtained the series solutions for four specific media whose respective density distributions in the direction perpendicular to the stratification plane are of an exponential, power-law type (one with exponent and the other with ) and a quadratic hyperbolic-secant. From these series solutions, we deduced exact solutions for the four media in terms of elemental functions. The exact solution for shock wave propagation in a medium of quadratic hyperbolic-secant density distribution is very appropriate to describe the growth of superbubbles in the Galactic disk.Facultad de Ciencias Astronómicas y Geofísica

The model for public television and the audience's expectations. Differences between Great Britain and Spain in the perception of qualities and obligations. El modelo de televisión pública y expectativas de la audiencia. Diferencias entre Gran Bretaña y España en la percepción de cualidades y obligaciones

Public service media (PSM) are in crisis throughout Europe. As a scenario for research, the two extremes of the background have been chosen: the first, BBC, is at the heart of media system, has become a model for the others and has just finished the particularly delicate challenge of renewal the fundamental law that is to rule over the next ten years; the second is on the periphery of public television, and in the extreme circumstances in Spain that have driven some of the television corporations to extinction, such as Canal 9 -Radiotelevisió Valenciana (RTVV). Using a method based on the use of semi-structured interviews and Delphi, the conception of these media models among their respective audiences is explored. Los medios de comunicación públicos están en crisis en toda Europa. Como escenario de la investigación, han sido elegidos dos extremos: el primero está en el corazón del sistema mediático, con la BBC que se ha convertido en modelo para el resto, y que acaba de terminar su particular reto de renovar la ley fundamental que va a regirla durante los próximos once años; el segundo está en la periferia de la television pública, en unas circunstancias extremas en España que han llevado a algunas corporaciones a la extinción, como en el caso de Canal 9 - Radiotelevisió Valenciana (RTVV). Utilizando entrevistas semiestructuradas y Delphi, exploraremos estos modelos mediáticos entre sus respectivas audiencias

Public service media funding. Future and state of the question in the british and spanish systems

PSM are not going through their finest moment. Adequate funding to ensure their survival is one of the fundamental factors that will shape their future. This paper takes a look at and compares the history of British and Spanish PSM, two very different systems. In both cases, they have suffered from cutbacks, though on a very different scale. In general, the mechanisms for obtaining necessary budgets are still bound to their respective traditions. Resumen Los medios audiovisuales públicos no están en su mejor momento. Una adecuada financiación que permita su supervivencia es uno de los factores fundamentales que marcarán el futuro. Este artículo recorre la historia de los sistemas mediáticos británico y español y los compara. En ambos casos, han sufrido recortes, aunque en escala muy distinta. Los mecanismos para obtener el presupuesto necesario están aún ligados a las tradiciones respectivas