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

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} $. The theory allows to compute the three and higher density correlators without any assumption.We find that the connected N-points density scales as r_1^{N(D-3)}, when$ 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&

Pisces, Gymnotiformes, Hypopomidae, <i>Brachyhypopomus</i> Mago-Leccia, 1994: First country record of three species of the genus, Argentina

Brachyhypopomus bombilla, B. draco and B. gauderio are recorded for the first time in freshwaters of Argentina.These species were collected in the Río Paraná basin at the Iberá Wetlands and Pre-Delta National Park. Brachyhypopomusbombilla, B. draco and B. gauderio can be sympatric and syntopic in Pre-Delta National Park, whereas B. bombilla andB. gauderio occupy the same environments in the Iberá Wetlands. Some records of B. brevirostris for Argentina aremisidentifications of B. gauderio, whereas others could correspond to one of these three species

Quasi-Classical Study of the Photodissociation Dynamics of the Methyl Radical

3 pags., 1 fig., 1 tab. -- PACS: Semiclassical theories and applications, 03.65.Sq; Excitation energies and lifetimes, oscillator strenghts 31.15.ag; Surface crossings, non-adiabatic couplings, 31.50.GhPeer reviewe