485 research outputs found
Systematic and biostratigraphic significance of a chinchillid rodent from the Pliocene of eastern Argentina
Two species of chinchillid rodents, Lagostomus (Lagostomopsis) incisus and âLagostomus (Lagostomopsis) spicatusâ, have been recorded from the Monte Hermoso Formation (MontehermosanâLower Chapadmalalan, Early Pliocene) of southern Buenos Aires Province, eastern Argentina. L. (L.) incisus is based on skull remains,while âL. (L.) spicatusâ is based on mandible remains and fragmentary skulls. Detailed study of specimens recovered from the upper section of the Monte Hermoso Formation, from the Irene âFormationâ, and the Chapadmalal Formation (late Earlyâearly Late Pliocene, Buenos Aires Province), some of them represented by associated skull and mandible remains, indicates that L. (L.) incisus and âL. (L.) spicatusâ are synonymous, with the valid name being L. (L.) incisus. The differences between both nominal species are here attributed to different ontogenetic states and sexual dimorphism. The stratigraphic provenance of the fossil material of L. (L.) incisus indicates a temporal distribution of this species restricted to the Montehermosan?âChapadmalalan (Earlyâearly Late Pliocene), instead of the Montehermosan (Early Pliocene).Facultad de Ciencias Naturales y Muse
Induced folding in RNA recognition by Arabidopsis thaliana DCL1
DCL1 is the ribonuclease that carries out miRNA biogenesis in plants. The enzyme has two tandem double stranded RNA binding domains (dsRBDs) in its C-terminus. Here we show that the first of these domains binds precursor RNA fragments when isolated and cooperates with the second domain in the recognition of substrate RNA. Remarkably, despite showing RNA binding activity, this domain is intrinsically disordered. We found that it acquires a folded conformation when bound to its substrate, being the first report of a complete dsRBD folding upon binding. The free unfolded form shows tendency to adopt folded conformations, and goes through an unfolded bound state prior to the folding event. The significance of these results is discussed by comparison with the behavior of other dsRBDs.Fil: Suarez, Irina Paula. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - Rosario. Instituto de BiologĂa Molecular y Celular de Rosario. Universidad Nacional de Rosario. Facultad de Ciencias BioquĂmicas y FarmacĂ©uticas. Instituto de BiologĂa Molecular y Celular de Rosario; ArgentinaFil: Burdisso, Paula. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - Rosario. Instituto de BiologĂa Molecular y Celular de Rosario. Universidad Nacional de Rosario. Facultad de Ciencias BioquĂmicas y FarmacĂ©uticas. Instituto de BiologĂa Molecular y Celular de Rosario; ArgentinaFil: Benoit Matthieu P. M. H.. Institut de Biologie Structurale Jean Pierre Ebel; FranciaFil: Boisbouvier, Jerome. Institut de Biologie Structurale Jean Pierre Ebel; FranciaFil: Rasia, Rodolfo Maximiliano. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - Rosario. Instituto de BiologĂa Molecular y Celular de Rosario. Universidad Nacional de Rosario. Facultad de Ciencias BioquĂmicas y FarmacĂ©uticas. Instituto de BiologĂa Molecular y Celular de Rosario; Argentin
Weighing simulated galaxy clusters using lensing and X-ray
We aim at investigating potential biases in lensing and X-ray methods to
measure the cluster mass profiles. We do so by performing realistic simulations
of lensing and X-ray observations that are subsequently analyzed using
observational techniques. The resulting mass estimates are compared among them
and with the input models. Three clusters obtained from state-of-the-art
hydrodynamical simulations, each of which has been projected along three
independent lines-of-sight, are used for this analysis. We find that strong
lensing models can be trusted over a limited region around the cluster core.
Extrapolating the strong lensing mass models to outside the Einstein ring can
lead to significant biases in the mass estimates, if the BCG is not modeled
properly for example. Weak lensing mass measurements can be largely affected by
substructures, depending on the method implemented to convert the shear into a
mass estimate. Using non-parametric methods which combine weak and strong
lensing data, the projected masses within R200 can be constrained with a
precision of ~10%. De-projection of lensing masses increases the scatter around
the true masses by more than a factor of two due to cluster triaxiality. X-ray
mass measurements have much smaller scatter (about a factor of two smaller than
the lensing masses) but they are generally biased low by 5-20%. This bias is
ascribable to bulk motions in the gas of our simulated clusters. Using the
lensing and the X-ray masses as proxies for the true and the hydrostatic
equilibrium masses of the simulated clusters and averaging over the cluster
sample we are able to measure the lack of hydrostatic equilibrium in the
systems we have investigated.Comment: 27 pages, 21 figures, accepted for publication on A&A. Version with
full resolution images can be found at
http://pico.bo.astro.it/~massimo/Public/Papers/massComp.pd
Cool Core Clusters from Cosmological Simulations
We present results obtained from a set of cosmological hydrodynamic
simulations of galaxy clusters, aimed at comparing predictions with
observational data on the diversity between cool-core (CC) and non-cool-core
(NCC) clusters. Our simulations include the effects of stellar and AGN feedback
and are based on an improved version of the smoothed particle hydrodynamics
code GADGET-3, which ameliorates gas mixing and better captures gas-dynamical
instabilities by including a suitable artificial thermal diffusion. In this
Letter, we focus our analysis on the entropy profiles, the primary diagnostic
we used to classify the degree of cool-coreness of clusters, and on the iron
profiles. In keeping with observations, our simulated clusters display a
variety of behaviors in entropy profiles: they range from steadily decreasing
profiles at small radii, characteristic of cool-core systems, to nearly flat
core isentropic profiles, characteristic of non-cool-core systems. Using
observational criteria to distinguish between the two classes of objects, we
find that they occur in similar proportions in both simulations and in
observations. Furthermore, we also find that simulated cool-core clusters have
profiles of iron abundance that are steeper than those of NCC clusters, which
is also in agreement with observational results. We show that the capability of
our simulations to generate a realistic cool-core structure in the cluster
population is due to AGN feedback and artificial thermal diffusion: their
combined action allows us to naturally distribute the energy extracted from
super-massive black holes and to compensate for the radiative losses of
low-entropy gas with short cooling time residing in the cluster core.Comment: 6 pages, 4 figures, accepted in ApJL, v2 contains some modifications
on the text (results unchanged
Thermal Conduction in Simulated Galaxy Clusters
We study the formation of clusters of galaxies using high-resolution
hydrodynamic cosmological simulations that include the effect of thermal
conduction with an effective isotropic conductivity of 1/3 the classical
Spitzer value. We find that, both for a hot ( keV) and
several cold ( keV) galaxy clusters, the baryonic fraction
converted into stars does not change significantly when thermal conduction is
included. However, the temperature profiles are modified, particularly in our
simulated hot system, where an extended isothermal core is readily formed. As a
consequence of heat flowing from the inner regions of the cluster both to its
outer parts and into its innermost resolved regions, the entropy profile is
altered as well. This effect is almost negligible for the cold cluster, as
expected based on the strong temperature dependence of the conductivity. Our
results demonstrate that while thermal conduction can have a significant
influence on the properties of the intra--cluster medium of rich galaxy
clusters, it appears unlikely to provide by itself a solution for the
overcooling problem in clusters, or to explain the current discrepancies
between the observed and simulated properties of the intra--cluster medium.Comment: 4 Pages, 3 Figures, Submitted to ApJ-Letter
Cosmological hydrodynamical simulations of galaxy clusters: X-ray scaling relations and their evolution
We analyse cosmological hydrodynamical simulations of galaxy clusters to
study the X-ray scaling relations between total masses and observable
quantities such as X-ray luminosity, gas mass, X-ray temperature, and .
Three sets of simulations are performed with an improved version of the
smoothed particle hydrodynamics GADGET-3 code. These consider the following:
non-radiative gas, star formation and stellar feedback, and the addition of
feedback by active galactic nuclei (AGN). We select clusters with , mimicking the typical selection of
Sunyaev-Zeldovich samples. This permits to have a mass range large enough to
enable robust fitting of the relations even at . The results of the
analysis show a general agreement with observations. The values of the slope of
the mass-gas mass and mass-temperature relations at are 10 per cent lower
with respect to due to the applied mass selection, in the former case,
and to the effect of early merger in the latter. We investigate the impact of
the slope variation on the study of the evolution of the normalization. We
conclude that cosmological studies through scaling relations should be limited
to the redshift range , where we find that the slope, the scatter, and
the covariance matrix of the relations are stable. The scaling between mass and
is confirmed to be the most robust relation, being almost independent of
the gas physics. At higher redshifts, the scaling relations are sensitive to
the inclusion of AGNs which influences low-mass systems. The detailed study of
these objects will be crucial to evaluate the AGN effect on the ICM.Comment: 24 pages, 11 figures, 5 tables, replaced to match accepted versio
Systematic and biostratigraphic significance of a chinchillid rodent from the Pliocene of eastern Argentina
Two species of chinchillid rodents, Lagostomus (Lagostomopsis) incisus and âLagostomus (Lagostomopsis) spicatusâ, have been recorded from the Monte Hermoso Formation (MontehermosanâLower Chapadmalalan, Early Pliocene) of southern Buenos Aires Province, eastern Argentina. L. (L.) incisus is based on skull remains,while âL. (L.) spicatusâ is based on mandible remains and fragmentary skulls. Detailed study of specimens recovered from the upper section of the Monte Hermoso Formation, from the Irene âFormationâ, and the Chapadmalal Formation (late Earlyâearly Late Pliocene, Buenos Aires Province), some of them represented by associated skull and mandible remains, indicates that L. (L.) incisus and âL. (L.) spicatusâ are synonymous, with the valid name being L. (L.) incisus. The differences between both nominal species are here attributed to different ontogenetic states and sexual dimorphism. The stratigraphic provenance of the fossil material of L. (L.) incisus indicates a temporal distribution of this species restricted to the Montehermosan?âChapadmalalan (Earlyâearly Late Pliocene), instead of the Montehermosan (Early Pliocene).Facultad de Ciencias Naturales y Muse
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