44 research outputs found
Diet of Hyphessobrycon auca (Pisces, characidae) in Iberá Wetland (Northeastern, Argentina)
Hyphessobrycon auca Almirón, Casciotta, Bechara & Ruiz Díaz, 2004, inhabit small lakes located at the northwest of Iberá wetland in Argentina. This research describes sorne aspects of its feeding. Samples were collected from its type locality from 2007 to 2009. Analysis of 70 digestive tracts of individuals ranging from 24 to 56 mm standard length (SL) showed that higher plants, algae, and quironomids larvae dominated the diet in terms of relative volume and occurrence frequency. Therefore, this species was characterized as omnivorous, but there was a growing trend towards herbivory when size class incremed. Smaller size class (< 35 mm SL) fed on higher proportion of animal preys such as quironomids larvae and protozoans, in contrast to larger ones who consumed almost exclusively plants and algae
CENSORS: A Combined EIS-NVSS Survey Of Radio Sources. I. Sample definition, radio data and optical identifications
A new sample of radio sources, with the designated name CENSORS (A Combined
EIS-NVSS Survey Of Radio Sources), has been defined by combining the NRAO VLA
Sky Survey (NVSS) at 1.4 GHz with the ESO Imaging Survey (EIS) Patch D, a 3 by
2 degree region of sky centred at 09 51 36.0, -21 00 00 (J2000). New radio
observations of 199 NVSS radio sources with NVSS flux densities S(1.4GHz) >
7.8mJy are presented, and compared with the EIS I-band imaging observations
which reach a depth of I~23; optical identifications are obtained for over
two-thirds of the ~150 confirmed radio sources within the EIS field. The radio
sources have a median linear size of 6 arcseconds, consistent with the trend
for lower flux density radio sources to be less extended. Other radio source
properties, such as the lobe flux density ratios, are consistent with those of
brighter radio source samples. From the optical information, 30-40% of the
sources are expected to lie at redshifts z >~ 1.5.
One of the key goals of this survey is to accurately determine the high
redshift evolution of the radio luminosity function. These radio sources are at
the ideal flux density level to achieve this goal; at redshifts z~2 they have
luminosities which are around the break of the luminosity function and so
provide a much more accurate census of the radio source population at those
redshifts than the existing studies of extreme, high radio power sources. Other
survey goals include investigating the dual--population unification schemes for
radio sources, studying the radio luminosity dependence of the evolution of
radio source environments, and understanding the radio power dependence of the
K-z relation for radio galaxies.Comment: Accepted for publication in MNRAS. 28 pages plus 36 reduced
resolution jpeg figures. A postscript version with full resolution figures
included in the text is available from
http://www.roe.ac.uk/~pnb/censors.ps.g
Factor de condición relativo de Leporinus Acutidens (v alenciennes, 1837) (pisces, anostomidae) en el Alto Rio Paraná, aguas abajo de la Represa Yacyretá
Leoporinus. Acutidens (Valenciennes, 1837) es una de las especies más abundantes del Alto río Paraná. El objetivo del presente trabajo fue evaluar los cambios espacio-temporales en el estado de bienestar de sus poblaciones en un tramo de este río, aguas abajo de la represa Yacyretá. Los peces fueron colectados, desde julio de 2009 a junio de 2013, con una batería de redes agalleras en dos sitios seleccionados en relación con su distancia a la represa (Ituzaingó = 1 km aguas abajo; Itá Ibaté = 90 km aguas abajo). Se aplicó un análisis factorial de la covarianza a fin de evaluar el efecto del sexo, sitios y ciclo hidrológico (2009/10, 2010/11, 2011/12, 2012/13) sobre el factor de condición relativo Kn, de los peces. Los resultados mostraron que el factor fue siempre superior en las hembras. Las diferencias entre sitios de muestreo no fueron significativas, aunque se registraron valores de Kn, más elevados en Itá Ibaté. Además, se detectó un efecto significativo del ciclo hidrológico (p < 0,05), con valores de Kn, mayores en ciclos con inundaciones más pronunciadas. Los resultados obtenidos demuestran el fuerte efecto modelador del régimen hidrológico sobre las poblaciones de L. acutidens en este tramo del río Paraná
Quasi-classical trajectories study of Ne2Br2(B) vibrational predissociation: Kinetics and product distributions
The vibrational predissociation of the Ne2Br2(B) van der Waals complex has
been investigated using the quasi-classical trajectory method (QCT), in the
range of vibrational levels v' = 16-23. Extensive comparison is made with the
most recent experimental observations [Pio et al., J. Chem. Phys. 133, 014305
(2010)], molecular dynamics with quantum transitions (MDQT) simulations [Miguel
et al., Faraday Discuss. 118, 257 (2001)], and preliminary results from
24-dimensional Cartesian coupled coherent state (CCCS) calculations. A
sequential mechanism is found to accurately describe the theoretical dynamical
evolution of intermediate and final product populations, and both QCT and CCCS
provide very good estimates for the dissociation lifetimes. The capabilities of
QCT in the description of the fragmentation kinetics is analyzed in detail by
using reduced-dimensionality models of the complexes and concepts from
phase-space transport theory. The problem of fast decoupling of the different
coherent states in CCCS simulations, resulting from the high dimensionality of
phase space, is tackled using a re-expansion scheme. QCT ro-vibrational product
state distributions are reported. Due to the weakness of the vdW couplings and
the low density of vibrational states, QCT predicts a larger than observed
propensity for \Delta v' = -1 and -2 channels for the respective dissociation
of the first and second Ne atoms.Comment: 16 pages, 6 figures, 4 tables. Accepted for publication in J. Chem.
Phy
Fractal Dimensions and Scaling Laws in the Interstellar Medium and Galaxy Distributions: a new Field Theory Approach
We develop a field theoretical approach to the cold interstellar medium (ISM) and large structure of the universe. We show that a non-relativistic self- gravitating gas in thermal equilibrium with variable number of atoms or fragments is exactly equivalent to a field theory of a scalar field phi(x) with exponential self-interaction. We analyze this field theory perturbatively and non-perturbatively through the renormalization group(RG).We show scaling behaviour (critical) for a continuous range of the physical parameters as the temperature. We derive in this framework the scaling relation M(R) \sim R^{d_H} for the mass on a region of size R, and Delta v \sim R^\frac12(d_H -1) for the velocity dispersion. For the density-density correlations we find a power-law behaviour for large distances \sim |r_1 - r_2|^{2D - 6}.The fractal dimension D turns to be related with the critical exponent \nu by D = 1/ \nu. Mean field theory yields \nu = 1/2, D = 2. Both the Ising and the mean field values are compatible with the present ISM observational data:1.4\leq D \leq 2. We develop a field theoretical approach to the galaxy distribution considering a gas of self-gravitating masses on the FRW background, in quasi-thermal equi- librium. We show that it exhibits scaling behaviour by RG methods. The galaxy correlations are computed without assuming homogeneity. We find \sim r^{D-3} r_1 >> r_i
EGG: hatching a mock Universe from empirical prescriptions⋆
This paper introduces EGG, the Empirical Galaxy Generator, a tool designed
within the ASTRODEEP collaboration to generate mock galaxy catalogs for deep
fields with realistic fluxes and simple morphologies. The simulation procedure
is based exclusively on empirical prescriptions -- rather than first principles
-- to provide the most accurate match with observations at 0<z<7. In
particular, we consider that galaxies can be either quiescent or star-forming,
and use their stellar mass (M*) and redshift (z) as the fundamental properties
from which all the other observables can be statistically derived. Drawing z
and M* from the observed galaxy stellar mass functions, we associate a star
formation rate (SFR) to each galaxy from the tight SFR-M* main sequence, while
dust attenuation, optical colors and morphologies (including bulge-to-total
ratios, sizes and aspect ratios) are obtained from empirical relations that we
establish from the high quality Hubble and Herschel observations available in
the CANDELS fields. Random scatter is introduced in each step to reproduce the
observed distributions of each parameter. Based on these observables, a
panchromatic spectral energy distribution (SED) is selected for each galaxy and
synthetic photometry is produced by integrating the redshifted SED in common
broad-band filters. Finally, the mock galaxies are placed on the sky at random
positions with a fixed angular two-point correlation function to implement
basic clustering. The resulting flux catalogs reproduce accurately the observed
number counts in all broad bands from the ultraviolet up to the sub-millimeter,
and can be directly fed to image simulators such as Skymaker. The images can
then be used to test source extraction softwares and image-based techniques
such as stacking. EGG is open-source, and is made available to the community
together with a set of pre-generated catalogs and images.Comment: 24 pages, 18 figures, accepted for publication in A&
Trayectorias creyentes/trayectorias sociales
Dentro de una sociedad crecientemente desregulada religiosamente, como lo
es la sociedad moderna, es progresiva la construcción de identidades religiosas
a partir de la experiencia de los sujetos (Dubar, 2000). Dentro de esta construcción identitaria es posible encontrar trayectorias creyentes (Hervieu-Léger,
2000) que propongan extender los valores propios del ámbito religioso a ciertos
espacios de lo secular, a partir de la inserción del individuo en dicho ámbito.
En este sentido, es importante identifi car y describir correctamente el o los
ámbitos de partida (instancias institucionales de la socialización religiosa) y el o los ámbitos de transición y de llegada, particularmente cuando esta
última se ubica claramente en la esfera secular.
Es el propósito de este trabajo identificar, describir y analizar un ejemplo de
trayectoria creyente/trayectoria social, que transita desde un ámbito específicamente religioso, en este caso el catolicismo, a un ámbito específicamente secular,
como lo es el sindicalismo. Concretamente, analizaremos el caso de la Juventud
Obrera Católica (JOC) como una instancia de socialización religiosa de jóvenes
trabajadores por parte de la Iglesia católica. A continuación presentaremos una
biografía, la de Emilio Máspero, dirigente sindical formado originalmente en
la JOC y que llegó a ocupar por más de 30 años el cargo de secretario general
de la Central Latinoamericana de Trabajadores (CLAT)