1,228 research outputs found
Moduli Spaces and Formal Operads
Let overline{M}_{g,n} be the moduli space of stable algebraic curves of genus
g with n marked points. With the operations which relate the different moduli
spaces identifying marked points, the family (overline{M}_{g,n})_{g,n} is a
modular operad of projective smooth Deligne-Mumford stacks, overline{M}. In
this paper we prove that the modular operad of singular chains
C_*(overline{M};Q) is formal; so it is weakly equivalent to the modular operad
of its homology H_*(overline{M};Q). As a consequence, the "up to homotopy"
algebras of these two operads are the same. To obtain this result we prove a
formality theorem for operads analogous to Deligne-Griffiths-Morgan-Sullivan
formality theorem, the existence of minimal models of modular operads, and a
characterization of formality for operads which shows that formality is
independent of the ground field.Comment: 36 pages (v3: some typographical corrections
A Cartan-Eilenberg approach to Homotopical Algebra
In this paper we propose an approach to homotopical algebra where the basic
ingredient is a category with two classes of distinguished morphisms: strong
and weak equivalences. These data determine the cofibrant objects by an
extension property analogous to the classical lifting property of projective
modules. We define a Cartan-Eilenberg category as a category with strong and
weak equivalences such that there is an equivalence between its localization
with respect to weak equivalences and the localised category of cofibrant
objets with respect to strong equivalences. This equivalence allows us to
extend the classical theory of derived additive functors to this non additive
setting. The main examples include Quillen model categories and functor
categories with a triple, in the last case we find examples in which the class
of strong equivalences is not determined by a homotopy relation. Among other
applications, we prove the existence of filtered minimal models for \emph{cdg}
algebras over a zero-characteristic field and we formulate an acyclic models
theorem for non additive functors
A multi-domain approach to asteroid families identification
Previous works have identified families halos by an analysis in proper
elements domains, or by using Sloan Digital Sky Survey-Moving Object Catalog
data, fourth release (SDSS-MOC4) multi-band photometry to infer the asteroid
taxonomy, or by a combination of the two methods. The limited number of
asteroids for which geometric albedo was known until recently discouraged in
the past the extensive use of this additional parameter, which is however of
great importance in identifying an asteroid taxonomy. The new availability of
geometric albedo data from the Wide-field Infrared Survey Explorer (WISE)
mission for about 100,000 asteroids significantly increased the sample of
objects for which such information, with some errors, is now known.
In this work we proposed a new method to identify families halos in a
multi-domain space composed by proper elements, SDSS-MOC4 (a*,i-z) colors, and
WISE geometric albedo for the whole main belt (and the Hungaria and Cybele
orbital regions). Assuming that most families were created by the breakup of an
undifferentiated parent body, they are expected to be homogeneous in colors and
albedo. The new method is quite effective in determining objects belonging to a
family halo, with low percentages of likely interlopers, and results that are
quite consistent in term of taxonomy and geometric albedo of the halo members.Comment: 23 pages, 18 figures, 6 tables. Accepted for publication in MNRA
Dynamical analysis on cosmology
We use a dynamical system approach to study the cosmological viability of
gravity theories. The method consists of formulating the
evolution equations as an autonomous system of ODEs, using suitable variables.
The formalism is applied to a class of models in which and its solutions and corresponding stability are
analysed in detail. New accelerating solutions that can be attractors in the
phase space are found. We also find that this class of models does not exhibit
a matter-dominated epoch, a solution which is inconsistent with current
cosmological observations.Comment: 12 pages, 4 figures. Accepted for publication in Classical and
Quantum Gravit
The Systematic Status and Biology of Telmatobius montanus Lataste (Amphibia, Leptodactylidae)
The poorly known Telmatobius montanus was rediscovered in the high Andean mountains between Mendoza and Talca on the Argentinian- Chilean frontier. Morphological characters of the adults and tadpoles are described. There is convergence in male secondary sex characters toward the leptodactylid frogs of the genus Eupsophus (nodosus group).Material digitalizado en SEDICI gracias a la colaboración del Dr. Jorge Williams (FCNM-UNLP).Facultad de Ciencias Naturales y Muse
Evaporation Ages: a New Dating Method for Young Star Clusters
The ages of young star clusters are fundamental clocks to constrain the
formation and evolution of pre-main-sequence stars and their protoplanetary
disks and exoplanets. However, dating methods for very young clusters often
disagree, casting doubts on the accuracy of the derived ages. We propose a new
method to derive the kinematic age of star clusters based on the evaporation
ages of their stars. The method is validated and calibrated using hundreds of
clusters identified in a supernova-driven simulation of the interstellar medium
forming stars for approximately 40 Myr within a 250 pc region. We demonstrate
that the clusters' evaporation-age uncertainty can be as small as about 10% for
clusters with a large enough number of evaporated stars and small but realistic
observational errors. We have obtained evaporation ages for a pilot sample of
10 clusters, finding a good agreement with their published isochronal ages. The
evaporation ages will provide important constraints for modeling the
pre-main-sequence evolution of low-mass stars, as well as to investigate the
star-formation and gas-evaporation history of young clusters. These ages can be
more accurate than isochronal ages for very young clusters, for which
observations and models are more uncertain.Comment: 13 pages, 11 figures, 2 tables, submitted to A&A on Nov 14th, 202
Chemical abundances and kinematics of barium stars
In this paper we present an homogeneous analysis of photospheric abundances
based on high-resolution spectroscopy of a sample of 182 barium stars and
candidates. We determined atmospheric parameters, spectroscopic distances,
stellar masses, ages, luminosities and scale height, radial velocities,
abundances of the Na, Al, -elements, iron-peak elements, and s-process
elements Y, Zr, La, Ce, and Nd. We employed the local-thermodynamic-equilibrium
model atmospheres of Kurucz and the spectral analysis code {\sc moog}. We found
that the metallicities, the temperatures and the surface gravities for barium
stars can not be represented by a single gaussian distribution. The abundances
of -elements and iron peak elements are similar to those of field giants
with the same metallicity. Sodium presents some degree of enrichment in more
evolved stars that could be attributed to the NeNa cycle. As expected, the
barium stars show overabundance of the elements created by the s-process. By
measuring the mean heavy-element abundance pattern as given by the ratio
[s/Fe], we found that the barium stars present several degrees of enrichment.
We also obtained the [hs/ls] ratio by measuring the photospheric abundances of
the Ba-peak and the Zr-peak elements. Our results indicated that the [s/Fe] and
the [hs/ls] ratios are strongly anti-correlated with the metallicity. Our
kinematical analysis showed that 90% of the barium stars belong to the thin
disk population. Based on their luminosities, none of the barium stars are
luminous enough to be an AGB star, nor to become self-enriched in the s-process
elements. Finally, we determined that the barium stars also follow an
age-metallicity relation.Comment: 30 pages, 26 figures, 18 tables, accepted for publication in MNRA
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