564 research outputs found
A 3-mode, Variable Velocity Jet Model for HH 34
Variable ejection velocity jet models can qualitatively explain the
appearance of successive working surfaces in Herbig-Haro (HH) jets. This paper
presents an attempt to explore which features of the HH-34 jet can indeed be
reproduced by such a model. From previously published data on this object, we
find evidence for the existence of a 3-mode ejection velocity variability, and
then explore the implications of such a variability. From simple, analytic
considerations it is possible to show that the longer period modes produce a
modulation on the shorter period modes, resulting in the formation of
``trains'' of multiple knots. The knots observed close to the source of HH-34
could correspond to such a structure. Finally, a numerical simulation with the
ejection velocity variability deduced from the HH-34 data is computed. This
numerical simulation shows a quite remarkable resemblance with the observed
properties of the HH-34 jet.Comment: 28 pages LaTex, 10 postscript figure
Radiation from matter entrainment in astrophysical jets: the AGN case
Jets are found in a variety of astrophysical sources, from young stellar
objects to active galactic nuclei. In all the cases the jet propagates with a
supersonic velocity through the external medium, which can be inhomogeneous,
and inhomogeneities could penetrate into the jet. The interaction of the jet
material with an obstacle produces a bow shock in the jet in which particles
can be accelerated up to relativistic energies and emit high-energy photons. In
this work, we explore the active galactic nuclei scenario, focusing on the
dynamical and radiative consequences of the interaction at different jet
heights. We find that the produced high-energy emission could be detectable by
the current gamma-ray telescopes. In general, the jet-clump interactions are a
possible mechanism to produce (steady or flaring) high-energy emission in many
astrophysical sources in which jets are present.Comment: 4 pages, 2 figures. Accepted for publication in the Proceedings of
the 275 IAU Symposium: "Jets at all Scales", held in Buenos Aires, September
13-17, 201
Prólogo al libro: Derecho renovado del consumidor: entre la economía y el Derecho
La obra es un instrumento útil para estudiantes universitarios, profesionales e interesados en la protección del consumidor; cuyo interés se eleva cuanto mayor es el desarrollo tecnológico y el grado de sofisticación por el que se encamina la evolución de la sociedad actual.
Tanto la estructura y contenido del libro, como el enfoque multidisciplinar de las materias objeto de análisis responden al modelo del Espacio Europeo de Educación Superior (EEES), basado en la adquisición de competencias y desarrollo de habilidades por parte del alumno.
En la primera parte se estudian: (i) el contexto socioeconómico y jurídico internacional, (ii) el tratamiento de la publicidad, competencia desleal, venta a pérdida (iii) el consumidor-inversor, la contratación de derivados y la información como contenido fundamental (iv) control y aplicación judicial de las cláusulas abusivas, (vi) arbitraje de consumo y solución extrajudicial de controversias.
En la segunda parte se analizan 54 términos legales de uso necesario en el Derecho de la contratación y la acción del consumidor. Entre ellos: las Condiciones generales de la contratación. Consumidor. Contrato de adhesión. Cláusulas abusivas. Cláusulas no negociadas individualmente. Responsabilidad por producto defectuoso. Contratación Electrónica. servicios financieros. Garantías comerciales.
La originalidad de la obra reside en el enfoque económico y jurídico interdisciplinar en el que se desarrollan las materias estudiadas y en la doble metodología utilizada para analizar las distintos aspectos estudiados. De este modo, la finalidad docente de la obra se enriquece y combina con su aptitud para ser utilizada en la investigación
Jet-cloud interations and the brightening of the narrow line region in Seyfert galaxies
We study the kinematical and brightness evolution of emission line clouds in
the narrow line region (NLR) of Seyfert galaxies during the passage of a jet.
We derive a critical density above which a cloud remains radiative after
compression by the jet cocoon. The critical density depends mainly on the
cocoon pressure. Super-critical clouds increase in emission line brightness,
while sub-critical clouds generally are highly overheated reducing their
luminosity below that of the inter-cloud medium. Due to the pressure
stratification in the bow-shock of the jet, a cylindrical structure of nested
shells develops around the jet. The most compact and brightest compressed
clouds surround the cloud-free channel of the radio jet. To support our
analytical model we present a numerical simulation of a supersonic jet
propagating into a clumpy NLR. The position-velocity diagram of the simulated
H_alpha emission shows total line widths of the order of 500 km/s with
large-scale variations in the radial velocities of the clouds due to the
stratified pressure in the bow-shock region of the jet. Most of the luminosity
is concentrated in a few dense clouds surrounding the jet. These morphological
and kinematic signatures are all found in the well observed NLR of NGC1068 and
other Seyfert galaxies.Comment: 11 pages, 3 figures, accepted for publication in The Astrophysical
Journal Letter
Highly Collimated Jets and Wide-Angle Outflows in HH46/47: New Evidence from Spitzer IR Images
We present new details of the structure and morphology of the jets and
outflows in HH46/47 as seen in Spitzer infrared images from IRAC and MIPS,
reprocessed using the ``HiRes'' deconvolution technique. HiRes improves the
visualization of spatial morphology by enhancing resolution (to sub-arcsec
levels in IRAC bands) and removing the contaminating side lobes from bright
sources. In addition to sharper views of previously reported bow shocks, we
have detected: (i) the sharply-delineated cavity walls of the wide-angle
biconical outflow, seen in scattered light on both sides of the protostar, (ii)
several very narrow jet features at distances 400 AU to 0.1 pc from the star,
and, (iii) compact emissions at MIPS 24 micron coincident with the jet heads,
tracing the hottest atomic/ionic gas in the bow shocks.Comment: 11 pages, 4 Figures, Accepted for publication in ApJ(Letters
MHD Models of Axisymmetric Protostellar Jets
We present the results of a series of axisymmetric time-dependent
magnetohydrodynamic (MHD) simulations of the propagation of cooling, overdense
jets, motivated by the properties of outflows associated with young stellar
objects. A variety of initial field strengths and configurations are explored
for both steady and time-variable (pulsed) jets. Even apparently weak magnetic
fields with strengths B < 60 micro-G in the pre-shocked jet beam can have a
significant effect on the dynamics, for example by altering the density, width,
and fragmentation of thin shells formed by cooling gas. A linear analysis
predicts that axisymmetric pinch modes of the MHD Kelvin-Helmholtz instability
should grow only slowly for the highly supermagnetosonic jets studied here; we
find no evidence for them in our simulations. Some of our models appear
unstable to current-driven pinch modes, however the resulting pressure and
density variations induced in the jet beam are not large, making this mechanism
an unlikely source of emission knots in the jet beam. In the case of pulsed
jets, radial hoop stresses confine shocked jet material in the pulses to the
axis, resulting in a higher density in the pulses in comparison to purely
hydrodynamic models.Comment: 28 pages, 16 figures, accepted by Ap.
Reproductive inequalities in the acanthocephalan Corynosoma cetaceum: looking beyond "crowding" effects
Background: At present, much research effort has been devoted to investigate overall (average) responses of parasite populations to specific factors, e.g., density-dependence in fecundity or mortality. However, studies on parasite populations usually pay little attention to individual variation (inequality) in reproductive success. A previous study on the acanthocephalan Corynosoma cetaceum in franciscana dolphins, Pontoporia blainvillei, revealed no overall intensity-dependent, or microhabitat effects, on mass and fecundity of worms. In this study, we investigated whether the same factors could influence mass inequalities for this species of acanthocephalan.Methods: A total of 10,138 specimens of C. cetaceum were collected from 10 franciscana dolphins accidentally caught in Buenos Aires Province between 1988-1990. To investigate mass inequalities, all the specimens were sexed, and females were classified according to their developmental stage and weighted. Additionally, the relationship between biomass and fecundity (estimated as the number of acanthors) was investigated for some females. Inequalities in fecundity and biomass were assessed using standard methods, i.e. the Lorenz curve and the Gini coefficient (G).Results: We found a modest, but highly significant linear relationship between mass and fecundity. The G was very low (0.314) compared with that from other helminth species. G values were significantly lower in gravid females, which presumably exhibit a slow rate of growth. Also, G values significantly increased with total intensity, but only for gravid females, and the effect was more predictable considering only the number of gravid females.Conclusions: Apparently, competition between reproducing females increases inequality without producing crowding effects. Although the mechanism whereby this occurs is unclear, gravid females, at higher intensities, expanded their distribution and occupied gut chambers with contrasting environmental conditions, which might result in greater variability in body size. The observed inequalities are not expected to strongly influence the population genetics of C. cetaceum, but they reveal subtle individual effects beyond an overall population impact.Fil: Aznar Avendaño, Francisco Javier. Universidad de Valencia; EspañaFil: Hernández Orts, Jesús Servando. Universidad Nacional del Comahue. Centro de Investigación Aplicada y Transferencia Tecnológica en Recursos Marinos "Almirante Storni". - Provincia de Río Negro. Ministerio de Agricultura, Ganadería y Pesca. Centro de Investigación Aplicada y Transferencia Tecnológica en Recursos Marinos "Almirante Storni". Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet Centro Nacional Patagónico. Centro de Investigación Aplicada y Transferencia Tecnológica en Recursos Marinos "Almirante Storni"; ArgentinaFil: Vélez Rubio, Gabriela Manuela. Universidad de Valencia; España. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de la República; UruguayFil: Fernández, Luis M.. Ceiba Foundation for Tropical Conservation; Estados UnidosFil: Muriel, Nadia T.. No especifíca;Fil: Raga, Juan Antonio. Universidad de Valencia; Españ
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