348 research outputs found
On the chemical composition of Titan's dry lakebed evaporites
Titan, the main satellite of Saturn, has an active cycle of methane in its
troposphere. Among other evidence for a mechanism of evaporation at work on the
ground, dry lakebeds have been discovered. Recent Cassini infrared observations
of these empty lakes have revealed a surface composition poor in water ice
compared to that of the surrounding terrains --- suggesting the existence of
organic evaporites deposits. The chemical composition of these possible
evaporites is unknown. In this paper, we study evaporite composition using a
model that treats both organic solids dissolution and solvent evaporation. Our
results suggest the possibility of large abundances of butane and acetylene in
the lake evaporites. However, due to uncertainties of the employed theory,
these determinations have to be confirmed by laboratory experiments.Comment: Icarus, in pres
Rigidification of quasi-categories
We give a new construction for rigidifying a quasi-category into a simplicial
category, and prove that it is weakly equivalent to the rigidification given by
Lurie. Our construction comes from the use of necklaces, which are simplicial
sets obtained by stringing simplices together. As an application of these
methods, we use our model to reprove some basic facts from Lurie's "Higher
Topos Theory" regarding the rigidification process.Comment: 26 page
Photochemical enrichment of deuterium in Titan's atmosphere: new insights from Cassini-Huygens
Cassini-Huygens data are used to re-examine the potential sources of the D/H
enhancement over solar, measured in methane, in Titan's atmosphere. Assuming
that the system is closed with respect to carbon, the use of constraints from
the Huygens probe for the determination of the current mass of atmospheric
methane and the most up-to-date determination of D/H from Cassini/CIRS infrared
spectra allow us to show that photochemical enrichment of deuterium is not
sufficient to be the sole mechanism yielding the measured D/H value. A possible
fractionation between CH3D and CH4 during the escape process may slightly
enhance the deuterium enrichment, but is not sufficient to explain the observed
D/H value over the range of escape values proposed in the literature. Hence,
alternative mechanisms such as a primordial deuterium enrichment must be
combined with the photochemical enrichment in Titan's atmosphere in order to
explain its current D/H value.Comment: 4 pages, 3 figures, accepted in ApJ
FullSWOF_Paral: Comparison of two parallelization strategies (MPI and SKELGIS) on a software designed for hydrology applications
In this paper, we perform a comparison of two approaches for the
parallelization of an existing, free software, FullSWOF 2D (http://www.
univ-orleans.fr/mapmo/soft/FullSWOF/ that solves shallow water equations for
applications in hydrology) based on a domain decomposition strategy. The first
approach is based on the classical MPI library while the second approach uses
Parallel Algorithmic Skeletons and more precisely a library named SkelGIS
(Skeletons for Geographical Information Systems). The first results presented
in this article show that the two approaches are similar in terms of
performance and scalability. The two implementation strategies are however very
different and we discuss the advantages of each one.Comment: 27 page
Clathration of Volatiles in the Solar Nebula and Implications for the Origin of Titan's atmosphere
We describe a scenario of Titan's formation matching the constraints imposed
by its current atmospheric composition. Assuming that the abundances of all
elements, including oxygen, are solar in the outer nebula, we show that the icy
planetesimals were agglomerated in the feeding zone of Saturn from a mixture of
clathrates with multiple guest species, so-called stochiometric hydrates such
as ammonia hydrate, and pure condensates. We also use a statistical
thermodynamic approach to constrain the composition of multiple guest
clathrates formed in the solar nebula. We then infer that krypton and xenon,
that are expected to condense in the 20-30 K temperature range in the solar
nebula, are trapped in clathrates at higher temperatures than 50 K. Once
formed, these ices either were accreted by Saturn or remained embedded in its
surrounding subnebula until they found their way into the regular satellites
growing around Saturn. In order to explain the carbon monoxide and primordial
argon deficiencies of Titan's atmosphere, we suggest that the satellite was
formed from icy planetesimals initially produced in the solar nebula and that
were partially devolatilized at a temperature not exceeding 50 K during their
migration within Saturn's subnebula. The observed deficiencies of Titan's
atmosphere in krypton and xenon could result from other processes that may have
occurred both prior or after the completion of Titan. Thus, krypton and xenon
may have been sequestrated in the form of XH3+ complexes in the solar nebula
gas phase, causing the formation of noble gas-poor planetesimals ultimately
accreted by Titan. Alternatively, krypton and xenon may have also been trapped
efficiently in clathrates located on the satellite's surface or in its
atmospheric haze.Comment: Accepted for publication in The Astrophysical Journa
A primordial origin for the atmospheric methane of Saturn's moon Titan
The origin of Titan's atmospheric methane is a key issue for understanding
the origin of the Saturnian satellite system. It has been proposed that
serpentinization reactions in Titan's interior could lead to the formation of
the observed methane. Meanwhile, alternative scenarios suggest that methane was
incorporated in Titan's planetesimals before its formation. Here, we point out
that serpentinization reactions in Titan's interior are not able to reproduce
the deuterium over hydrogen (D/H) ratio observed at present in methane in its
atmosphere, and would require a maximum D/H ratio in Titan's water ice 30%
lower than the value likely acquired by the satellite during its formation,
based on Cassini observations at Enceladus. Alternatively, production of
methane in Titan's interior via radiolytic reactions with water can be
envisaged but the associated production rates remain uncertain. On the other
hand, a mechanism that easily explains the presence of large amounts of methane
trapped in Titan in a way consistent with its measured atmospheric D/H ratio is
its direct capture in the satellite's planetesimals at the time of their
formation in the solar nebula. In this case, the mass of methane trapped in
Titan's interior can be up to 1,300 times the current mass of atmospheric
methane.Comment: Accepted for publication in Icaru
An experimental study of the mixing of COâ and Nâ under conditions found at the surface of Venus
Based on the only reliable temperature profile available in the deepest âŒ10 km layer above Venusâ surface (obtained by the VeGa-2 landing probe), the mixing conditions of the main constituents of Venusâs atmosphere, COâ and Nâ, have been questioned. In this work, we report the results of a series of experiments that were done in the GEER facility at Glenn Research Center to investigate the homogeneity of COâ/Nâ gas mixtures at 100 bars and temperatures ranging from âŒ296 K to âŒ735 K. When the gas mixtures are initially well-mixed, separation of the two gases based on their molecular mass does not occur over the time scales observed; although, small systematic variations in composition remain to be fully interpreted. However, when Nâ is injected on top of COâ (layered fill), the very large density ratio makes it more difficult to mix the two chemical species. Timescales of mixing are of the order of 10ÂČ hours over the height of the test vessel (roughly 60 cm), and even longer when the gas mixture is at rest and only molecular diffusion is occurring. At room temperature, close to the critical point of the mixture, large pressure variations are obtained for the layered fill, as Nâ slowly mixes into COâ. This can be explained by large density variations induced by the mixing. For conditions relevant to the near-surface atmosphere of Venus, separation of COâ and Nâ based on their molecular mass and due to physical properties of the gas mixture is not demonstrated, but can not be firmly excluded either. This suggests that if the compositional vertical gradient deduced from the VeGa-2 temperature profile is to be trusted, it would most probably be due to some extrinsic processes (not related to gas properties, e.g. COâ volcanic inputs) and large mixing time constants
Postweaning Enriched Environment Enhances Cognitive Function and Brain-Derived Neurotrophic Factor Signaling in the Hippocampus in Maternally Separated Rats
Adverse environments during early life may lead to different neurophysiological and behavioral consequences, including depression and learning and memory deficits that persist into adulthood. Previously, we demonstrated that exposure to an enriched environment during adolescence mitigates the cognitive impairment observed after maternal separation in a task-specific manner. However, underlying neural mechanisms are still not fully understood. The current study examines the effects of neonatal maternal separation (MS) and postweaning environmental enrichment (EE) on spatial learning and memory performance in a short version of the Barnes Maze, active and passive behaviors in the forced swim test, and on TrkB/BDNF receptor expression in the hippocampus. Our results revealed that MS impaired acquisition learning and that enriched rats performed better than non-enriched rats in acquisition trials, regardless of early conditions. During the probe, enriched-housed rats demonstrated better performance than those reared in standard conditions. No significant differences between groups were found in the forced swim test. Both MS and EE increase full-length TrkB expression, and the combination of MS and EE treatment caused the highest levels of this protein expression. Similarly, truncated TrkB expression was higher in the MS/EE group. Animal facility rearing (AFR) non-enriched groups present the lowest activation of phosphorylated Erk, a canonical downstream kinase of TrkB signaling. Taken together, our results demonstrate the importance of enriched environment as an intervention to ameliorate the effects of maternal separation on spatial learning and memory. TrkB/BDNF signaling could mediate neuroplastic changes related to learning and memory during exposure to enriched environment.Fil: Cordier, Javier Maximiliano. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - CĂłrdoba. Instituto de Diversidad y EcologĂa Animal. Universidad Nacional de CĂłrdoba. Facultad de Ciencias Exactas FĂsicas y Naturales. Instituto de Diversidad y EcologĂa Animal; ArgentinaFil: Aguggia, Julieta Paola. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - CĂłrdoba. Instituto de Investigaciones en Ciencias de la Salud. Universidad Nacional de CĂłrdoba. Instituto de Investigaciones en Ciencias de la Salud; ArgentinaFil: Danelon, VĂctor. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - CĂłrdoba. Instituto de Investigaciones BiolĂłgicas y TecnolĂłgicas. Universidad Nacional de CĂłrdoba. Facultad de Ciencias Exactas, FĂsicas y Naturales. Instituto de Investigaciones BiolĂłgicas y TecnolĂłgicas; ArgentinaFil: Mir, Franco Rafael. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas; Argentina. Universidad Nacional de La Rioja; Argentina. Universidad Nacional de CĂłrdoba. Facultad de Cs.exactas FĂsicas y Naturales. Departamento de FisiologĂa. CĂĄtedra de FisiologĂa Animal; ArgentinaFil: Rivarola, MarĂa AngĂ©lica. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - CĂłrdoba. Instituto de Investigaciones en Ciencias de la Salud. Universidad Nacional de CĂłrdoba. Instituto de Investigaciones en Ciencias de la Salud; Argentina. Universidad Nacional de CĂłrdoba. Facultad de Cs.exactas FĂsicas y Naturales. Departamento de FisiologĂa. CĂĄtedra de FisiologĂa Animal; ArgentinaFil: Masco, Daniel Hugo. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - CĂłrdoba. Instituto de Investigaciones BiolĂłgicas y TecnolĂłgicas. Universidad Nacional de CĂłrdoba. Facultad de Ciencias Exactas, FĂsicas y Naturales. Instituto de Investigaciones BiolĂłgicas y TecnolĂłgicas; Argentin
A Large Stellar Evolution Database for Population Synthesis Studies. III. Inclusion of the full Asymptotic Giant Branch phase and Web tools for stellar population analyses
Stellar evolution tracks and isochrones are key inputs for a wide range of
astrophysical studies; in particular, they are essential to the interpretation
of photometric and spectroscopic observations of resolved and unresolved
stellar populations. We have made available to the astrophysical community a
large, homogenous database of up-to-date stellar tracks and isochrones, and a
set of programs useful in population synthesis studies.
In this paper we first summarize the main properties of our stellar model
database (BaSTI) already introduced in Pietrinferni et al. (2004) and
Pietrinferni et al. (2006). We then discuss an important update of the
database, i.e., the extension of all stellar models and isochrones until the
end of the thermal pulses along the Asymptotic Giant Branch. This extension of
the library is particularly relevant for stellar population analyses in the
near-infrared, or longer wavelengths, where the contribution to the integrated
photometric properties by cool and bright Asymptotic Giant Branch stars is
significant. A few comparisons with empirical data are also presentend and
briefly discussed. We then present three web-tools that allow an interactive
access to the database, and make possible to compute user-specified
evolutionary tracks, isochrones, stellar luminosity functions, plus synthetic
Color-Magnitude-Diagrams and integrated magnitudes for arbitrary Star Formation
Histories. All these web tools are available at the BaSTI database official
site: http://www.oa-teramo.inaf.it/BASTI.Comment: 18 pages, 5 tables, 7 figures, accepted in The Astronomical Journal.
The BaSTI database and its web-tools are available on the web
http://www.oa-teramo.inaf.it/BASTI. The web-tools are also mirrored in the
BaSTI section of http://astro.ensc-rennes.f
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