7,004 research outputs found
Deep into the Water Fountains: The case of IRAS 18043-2116
(Abridged) The formation of large-scale (hundreds to few thousands of AU)
bipolar structures in the circumstellar envelopes (CSEs) of post-Asymptotic
Giant Branch (post-AGB) stars is poorly understood. The shape of these
structures, traced by emission from fast molecular outflows, suggests that the
dynamics at the innermost regions of these CSEs does not depend only on the
energy of the radiation field of the central star. Deep into the Water
Fountains is an observational project based on the results of programs carried
out with three telescope facilities: The Karl G. Jansky Very Large Array
(JVLA), The Australia Telescope Compact Array (ATCA), and the Very Large
Telescope (SINFONI-VLT). Here we report the results of the observations towards
the WF nebula IRAS 180432116: Detection of radio continuum emission in the
frequency range 1.5GHz - 8.0GHz; HO maser spectral features and radio
continuum emission detected at 22GHz, and H ro-vibrational emission lines
detected at the near infrared. The high-velocity HO maser spectral
features, and the shock-excited H emission detected could be produced in
molecular layers which are swept up as a consequence of the propagation of a
jet-driven wind. Using the derived H column density, we estimated a
molecular mass-loss rate of the order of Myr. On the
other hand, if the radio continuum flux detected is generated as a consequence
of the propagation of a thermal radio jet, the mass-loss rate associated to the
outflowing ionized material is of the order of 10Myr.
The presence of a rotating disk could be a plausible explanation for the
mass-loss rates estimated.Comment: 10 pages, 5 figures. Accepted for publication in A&
Permeabilidad de gases en membranas de zeolita ZSM-5
El trabajo incluido en el presente articulo tiene como objetivo analizar la influencia de la deposición de zeolita ZSM-5 en un tubo de alumina sobre la velocidad de transferencia de materia de distintos gases con el fin de analizar la capacidad de separación. Se ha evaluado la influencia de la presencia de zeolita, así como del caudal de gas alimentado y la temperatura a la que se desarrolla el proceso deseparación
La suplementación con creatina en el deporte y su relación con el rendimiento deportivo
Determination of the Kobayashi-Maskawa-Cabibbo matrix element V_{us} under various flavor-symmetry-breaking models in hyperon semileptonic decays
We study the success to describe hyperon semileptonic decays of four models
that incorporate second-order SU(3) symmetry breaking corrections. The criteria
to assess their success is by determining V_{us} in each of the three relevant
hyperon semileptonic decays and comparing the values obtained with one another
and also with the one that comes from K_{l3} decays. A strong dependence on the
particular symmetry breaking model is observed. Values of V_{us} which do not
agree with the one of K_{l3} are generally obtained. However, in the context of
chiral perturbation theory, only the model whose corrections are O(m_s) and
O(m_s^{3/2}) is successful. Using its predictions for the f_1 form factors one
can quote a value of V_{us} from this model, namely, V_{us}=0.2176\pm 0.0026,
which is in excellent agreement with the K_{l3} one.Comment: Final versio
Gases Separation by ZSM-5 based Membranes
AbstractPresent work analyses the effect produced by the presence of ZSM-5 zeolite in an alumina tube upon the permeation rate of different gases (nitrogen, oxygen, carbon dioxide and normal-butane). A comparison between experimental data of permeation through the membrane with and without ZSM-5 zeolite was performed with an increase in the resistance to transport more evident for n-butane. Also the influence of temperature upon permeation has been analyzed
Light propagation through optical media using metric contact geometry
In this work, we show that the orthogonality between rays and fronts of light
propagation in a medium is expressed in terms of a suitable metric contact
structure of the optical medium without boundaries. Moreover, we show that
considering interfaces (modeled as boundaries) orthogonality is no longer
fulfilled, leading to optical aberrations and in some cases total internal
reflection. We present some illustrative examples of this latter point.Comment: 8 pages, 7 figure
Crystallization and melting of bacteria colonies and Brownian Bugs
Motivated by the existence of remarkably ordered cluster arrays of bacteria
colonies growing in Petri dishes and related problems, we study the spontaneous
emergence of clustering and patterns in a simple nonequilibrium system: the
individual-based interacting Brownian bug model. We map this discrete model
into a continuous Langevin equation which is the starting point for our
extensive numerical analyses. For the two-dimensional case we report on the
spontaneous generation of localized clusters of activity as well as a
melting/freezing transition from a disordered or isotropic phase to an ordered
one characterized by hexagonal patterns. We study in detail the analogies and
differences with the well-established Kosterlitz-Thouless-Halperin-Nelson-Young
theory of equilibrium melting, as well as with another competing theory. For
that, we study translational and orientational correlations and perform a
careful defect analysis. We find a non standard one-stage, defect-mediated,
transition whose nature is only partially elucidated.Comment: 13 Figures. 14 pages. Submitted to Phys. Rev.
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