2,850 research outputs found
On the relation between the IR continuum and the active galactic nucleus in Seyfert galaxies
A sample of the brightest known Seyfert galaxies from the CfA sample is
analyzed on the basis of ISO photometric and spectroscopic data.
Regardless of the Seyfert type, the mid-IR continuum emission from these
galaxies is found to be correlated with the coronal line emission arising in
the nuclear active region. Conversely, the correlation degrades progressively
when moving from the mid- to the far-IR emission, where it ends to vanish. It
is concluded that the mid-IR emission is largely dominated by dust heated by
processes associated with the active nucleus whereas the far-IR is a different
component most probably unrelated with the active region. We suggest that the
far-IR component is due to dust heated by the stellar population in the disks
of these galaxies.Comment: 6 pages, 3 figures To be published in Astronomy and Astrophysic
Flux-cutting and flux-transport effects in type-II superconductor slabs in a parallel rotating magnetic field
The magnetic response of irreversible type-II superconductor slabs subjected
to in-plane rotating magnetic field is investigated by applying the circular,
elliptic, extended-elliptic, and rectangular flux-line-cutting critical-state
models. Specifically, the models have been applied to explain experiments on a
PbBi rotating disk in a fixed magnetic field , parallel to the flat
surfaces. Here, we have exploited the equivalency of the experimental situation
with that of a fixed disk under the action of a parallel magnetic field,
rotating in the opposite sense. The effect of both the magnitude of the
applied magnetic field and its angle of rotation upon the
magnetization of the superconductor sample is analyzed. When is smaller
than the penetration field , the magnetization components, parallel and
perpendicular to , oscillate with increasing the rotation angle. On
the other hand, if the magnitude of the applied field, , is larger than
, both magnetization components become constant functions of at
large rotation angles. The evolution of the magnetic induction profiles inside
the superconductor is also studied.Comment: 12 pages, 29 figure
Domain wall dynamics in an optical Kerr cavity
An anisotropic (dichroic) optical cavity containing a self-focusing Kerr
medium is shown to display a bifurcation between static --Ising-- and moving
--Bloch-- domain walls, the so-called nonequilibrium Ising-Bloch transition
(NIB). Bloch walls can show regular or irregular temporal behaviour, in
particular, bursting and spiking. These phenomena are interpreted in terms of
the spatio-temporal dynamics of the extended patterns connected by the wall,
which display complex dynamical behaviour as well. Domain wall interaction,
including the formation of bound states is also addressed.Comment: 15 pages Tex file with 11 postscript figures. Resubmitted to Phys.
Rev.
Self-organization of ultrasound in viscous fluids
We report the theoretical and experimental demonstration of pattern formation
in acoustics. The system is an acoustic resonator containing a viscous fluid.
When the system is driven by an external periodic force, the ultrasonic field
inside the cavity experiences different pattern-forming instabilities leading
to the emergence of periodic structures. The system is also shown to possess
bistable regimes, in which localized states of the ultrasonic field develop.
The thermal nonlinearity in the viscous fluid, together with the
far-from-equilibrium conditions, are is the responsible of the observed
effects
Bistable and dynamic states of parametrically excited ultrasound in a fluid-filled cavity
In this paper we have considered the problem of parametric sound generation
in an acoustic resonator flled with a fluid, taking explicitely into account
the influence of the nonlinearly generated second harmonic. A simple model is
presented, and its stationary solutions obtained. The main feature of these
solutions is the appearance of bistable states of the fundamental field
resulting from the coupling to the second harmonic. An experimental setup was
designed to check the predictions of the theory. The results are consistent
with the predicted values for the mode amplitudes and parametric thresholds. At
higher driving values a self-modulation of the amplitudes is observed. We
identify this phenomenon with a secondary instability previously reported in
the frame of the theoretical model.Comment: 5 figures. Submitted to JAS
Lista patrón de los tiburones, rayas y quimeras (Chondrichthyes, Elasmobranchii, Holocephali) de México
Llista patró dels taurons, rajades i quimeres (Chondrichthyes, Elasmobranchii, Holocephali) de Mèxic Es presenta una relació de les espècies de taurons, rajades i quimeres (condrictis) que han estat registrades a les aigües territorials de Mèxic, basada en revisions de bases de dades, literatura, examen físic dels espècimens de col·leccions científiques i registres d’exemplars recol·lectats en treballs de camp durant els darrers quatre anys i que no han estat publicats. La relació conté informació de 214 espècies de condrictis que, com a mínim, han estat registrades a les aigües marines i salobroses de Mèxic, pertanyents a 84 gèneres, 40 famílies i 14 ordres. S’hi inclouen vuit espècies de quimeres, 95 de batoïdeus i 111 de taurons. La condrictiofauna mexicana és una de les més riques del món, amb el 17,3% o més de les espècies conegudes. A més a més, s’ hi inclouen 16 espècies que és probable que siguin presents a Mèxic atesos els seus patrons de distribució.Checklist of sharks, rays and chimaeras (Chondrichthyes, Elasmobranchii, Holocephali) from Mexico We present an annotated checklist of the species of sharks, rays and chimaeras (chondrichthyan fishes) occurring in Mexican waters, based on a thorough review of the literature and electronic database searches, examination of museum collection specimens, and unpublished records obtained during fieldwork conducted in the last four years. The checklist contains information of at least 214 species of chondrichthyan fishes that occur in Mexican marine and brackish waters, assigned to 84 genera, 40 families and 14 orders. It includes eight species of chimaeras, 95 batoids and 111 sharks. Condrichthyan fauna in Mexico is one of the richest in the world, with almost 17.3% of the known species. An additional 16 species are included as their occurrence in Mexican marine waters is probable according to distributional patterns.Se presenta un listado anotado de las especies de tiburones, rayas y quimeras (Condrictios) que han sido registrados en las aguas territoriales de México, basado en revisiones de bases de datos, literatura, examinación física de los especímenes de colecciones científicas y de registros de ejemplares recolectados en campo durante los últimos cuatro años y que no han sido publicados. El listado contiene información de al menos 214 especies de condrictios que se han registrado en las aguas marinas y salobres de México, pertenecientes a 84 géneros, 40 familias y 14 órdenes. Se incluyen ocho especies de quimeras, 95 de batoideos y 111 de tiburones. La condrictiofauna mexicana es una de las más ricas a nivel mundial, con al menos 17.3% de las especies conocidas. Adicionalmente, 16 especies, se incluyen como especies probables que ocurran en México debido a sus patrones de distribución.Palabras clave: Condrictios, Elasmobranquios, Batoideos, Quimeras, México
Nondiffractive sonic crystals
We predict theoretically the nondiffractive propagation of sonic waves in
periodic acoustic media (sonic crystals), by expansion into a set of plane
waves (Bloch mode expansion), and by finite difference time domain calculations
of finite beams. We also give analytical evaluations of the parameters for
nondiffractive propagation, as well as the minimum size of the nondiffractively
propagating acoustic beams.Comment: 7 figures, submitted to J. Acoust. Soc. A
On the relation between the coronal line emission and the IR/X-ray emission in Seyfert galaxies
The relation between the X-ray, the coronal line and the infrared (IR)
emissions in a sample of the brightest known Seyfert galaxies is analysed. A
close relationship between the absorption-corrected soft X-ray emission and
both the mid-IR and the coronal line emission is found for the Seyfert type 2
objects in the sample. The coronal line and the X-ray emissions are both main
tracers of the central activity, hence their relationship with the mid-IR
emission points to nuclear energetic process as the main responsibles of the
heating of the circumnuclear dust. On the other hand, the above relations do
not seem to hold for the Seyfert type 1 discussed in the sample, at least when
the comparisons are done in a flux diagram. This is partially because of the
reduced number of objects of this type analysed in this work and the fact that
the measured soft X-ray emission in Seyfert 1s is systematically larger, by at
least an order of magnitude, than that in the Seyfert 2 counterparts. Finally,
the hard X-ray emission in the studied sample appears unrelated to either the
mid-IR or the coronal line emission.Comment: 14 pages, 3 figures To be published in MNRAS (accepted
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