7,109 research outputs found
Gender differences in time allocation of poor children in Colombia
This paper studies the e§ect of credit constraints and constraints on transfers between parents and children, on di§erences in labor and schooling across children within the same household, with an application to gender. When families are unconstrained in these respects, di§erences in labor supply or education are driven by di§erences in wages or returns to education. If the family faces an imperfect capital market, the labor supply of each child is ine¢ cient, but di§erences across children are still driven by comparative advantage. However, if interfamily transfers are constrained so that parents cannot o§set inequality between their children, they will favor the human capital accumulation of the more disadvantaged child -generally the one who works more as a child. We use our theory to examine the gender gap in child labor. Using a sample of poor families in Colombia, we conÖrm our prediction among rural households, although this is less clear for urban households. The gender gap is largely explained by the wage gap between girls and boys. Moreover, families with the potential to make capital transfers to adult children (e.g. those with large animals), can compensate adult sons for their greater child labor and reduced educational attainment. In such families, as predicted, the male/female labor gap isgreater.Child labor, schooling, credit constraints.
An operational framework for nonlocality
Due to the importance of entanglement for quantum information purposes, a
framework has been developed for its characterization and quantification as a
resource based on the following operational principle: entanglement among
parties cannot be created by local operations and classical communication, even
when parties collaborate. More recently, nonlocality has been identified
as another resource, alternative to entanglement and necessary for
device-independent quantum information protocols. We introduce an operational
framework for nonlocality based on a similar principle: nonlocality among
parties cannot be created by local operations and allowed classical
communication even when parties collaborate. We then show that the
standard definition of multipartite nonlocality, due to Svetlichny, is
inconsistent with this operational approach: according to it, genuine
tripartite nonlocality could be created by two collaborating parties. We
finally discuss alternative definitions for which consistency is recovered
Deformation of canonical morphisms and the moduli of surfaces of general type
In this article we study the deformation of finite maps and show how to use
this deformation theory to construct varieties with given invariants in a
projective space. Among other things, we prove a criterion that determines when
a finite map can be deformed to a one--to--one map. We use this criterion to
construct new simple canonical surfaces with different and . Our
general results enable us to describe some new components of the moduli of
surfaces of general type. We also find infinitely many moduli spaces having one component whose general point corresponds to a
canonically embedded surface and another component whose general point
corresponds to a surface whose canonical map is a degree 2 morphism.Comment: 32 pages. Final version with some simplifications and clarifications
in the exposition. To appear in Invent. Math. (the final publication is
available at springerlink.com
The distribution of stars around the Milky Way's central black hole II: Diffuse light from sub-giants and dwarfs
This is the second of three papers that search for the predicted stellar cusp
around the Milky Way's central black hole, Sagittarius A*, with new data and
methods. We aim to infer the distribution of the faintest stellar population
currently accessible through observations around Sagittarius A*. We use
adaptive optics assisted high angular resolution images obtained with the NACO
instrument at the ESO VLT. Through optimised PSF fitting we remove the light
from all detected stars above a given magnitude limit. Subsequently we analyse
the remaining, diffuse light density. The analysed diffuse light arises from
sub-giant and main-sequence stars with KS ~ 19 - 20 with masses of 1 - 2 Msol .
These stars can be old enough to be dynamically relaxed. The observed power-law
profile and its slope are consistent with the existence of a relaxed stellar
cusp around the Milky Way's central black hole. We find that a Nuker law
provides an adequate description of the nuclear cluster's intrinsic shape
(assuming spherical symmetry). The 3D power-law slope near Sgr A* is \gamma =
1.23 +- 0.05. At a distance of 0.01 pc from the black hole, we estimate a
stellar mass density of 2.3 +- 0.3 x 10^7 Msol pc^-3 and a total enclosed
stellar mass of 180 +- 20 Msol. These estimates assume a constant mass-to-light
ratio and do not take stellar remnants into account. The fact that no cusp is
observed for bright (Ks 16) giant stars at projected distances of roughly
0.1-0.3 pc implies that some mechanism has altered their appearance or
distribution.Comment: Accepted for publication A&
The distribution of old stars around the Milky Way's central black hole I: Star counts
(abridged) In this paper we revisit the problem of inferring the innermost
structure of the Milky Way's nuclear star cluster via star counts, to clarify
whether it displays a core or a cusp around the central black hole. Through
image stacking and improved PSF fitting we push the completeness limit about
one magnitude deeper than in previous, comparable work. Contrary to previous
work, we analyse the stellar density in well-defined magnitude ranges in order
to be able to constrain stellar masses and ages. The RC and brighter giant
stars display a core-like surface density profile within a projected radius
R<0.3 pc of the central black hole, in agreement with previous studies, but
show a cusp-like surface density distribution at larger R. The surface density
of the fainter stars can be described well by a single power-law at R<2 pc. The
cusp-like profile of the faint stars persists even if we take into account the
possible contamination of stars in this brightness range by young pre-main
sequence stars. The data are inconsistent with a core-profile for the faint
stars.Finally, we show that a 3D Nuker law provides a very good description of
the cluster structure. We conclude that the observed stellar density at the
Galactic Centre, as it can be inferred with current instruments, is consistent
with the existence of a stellar cusp around the Milky Way's central black hole,
Sgr A*. This cusp is well developed inside the influence radius of about 3 pc
of Sgr A* and can be described by a single three-dimensional power-law with an
exponent gamma=1.23+-0.05. The apparent lack of RC stars and brighter giants at
projected distances of R < 0.3 pc (R<8") of the massive black hole may indicate
that some mechanism has altered their distribution or intrinsic luminosity.Comment: Accepted for publication A&
A framework for closed-loop supply chains of reusable articles
Reuse practices contribute to the environmental and economical sustainability of production and distribution systems. Surprisingly, reuse closed-loop supply chains (CLSC) have not been widely researched for the moment. In this paper, we explore the scientific literature on reuse and we propose a framework for reusable articles. This conceptual structure includes a typology integrating under the reusable articles term different categories of articles (transportation items, packaging materials, tools) and addresses the management issues that arise in reuse CLSC. We ground our results in a set of case studies developed in real industrial settings, which have also been contrasted with cases available in existing literature.reverse logistics;case studies;closed-loop supply chains;returns managment
Transgressivity in Key Functional Traits Rather Than Phenotypic Plasticity Promotes Stress Tolerance in A Hybrid Cordgrass
Hybridization might promote offspring fitness via a greater tolerance to environmental stressors due to heterosis and higher levels of phenotypic plasticity. Thus, analyzing the phenotypic expression of hybrids provides an opportunity to elucidate further plant responses to environmental stress. In the case of coastal salt marshes, sea level rise subjects hybrids, and their parents, to longer tidal submergence and higher salinity. We analyzed the phenotypic expression patterns in the hybrid Spartina densiflora x foliosa relative to its parental species, native S. foliosa, and invasive S. densiflora, from the San Francisco Estuary when exposed to contrasting salinities and inundations in a mesocosm experiment. 37% of the recorded traits displayed no variability among parents and hybrids, 3% showed an additive inheritance, 37% showed mid-parent heterosis, 18% showed best-parent heterosis, and 5% presented worst-parent heterosis. Transgressivity, rather than phenotypic plasticity, in key functional traits of the hybrid, such as tiller height, conveyed greater stress tolerance to the hybrid when compared to the tolerance of its parents. As parental trait variability increased, phenotypic transgressivity of the hybrid increased and it was more important in response to inundation than salinity. Increases in salinity and inundation associated with sea level rise will amplify the superiority of the hybrid over its parental species. These results provide evidence of transgressive traits as an underlying source of adaptive variation that can facilitate plant invasions. The adaptive evolutionary process of hybridization is thought to support an increased invasiveness of plant species and their rapid evolution
Greens function for time-harmonic elastodynamics in a half-space with hysteretic damping
Se presenta una solución analÃtica para la respuesta de un semiespacio tridimensional homogéneo con una carga puntual armónica en el tiempo. Esta expresión es de gran importancia debido a que se puede emplear como solución fundamental en el Método de los Elementos de Contorno para la resolución de problemas elastodinámicos tridimensionales de semiespacios. Las expresiones se han validado comparando los resultados con otros empleados en el Método de Elementos de Contorno en los que es necesaria la discretización de la superficie del semiespacio. También se ha comparado con otras soluciones para el semiespacio en 2.5D y con resultados experimentales obtenidos de referencias bibliográficas.
Por último, se estudia el comportamiento asintótico de la solución para diferentes estados comparando los resultados con soluciones fundamentales existentes.This paper presents an analytical solution for the steady-state response of a homogeneous three-dimensional half-space subject to a time-harmonic point load. This expresion is of great importance in the formulation of three-dimensional elastodynamic problems in a half-space by means of boundary element methods which can be employed as a Fundamental Solution. The expressions are validated comparing the results with those obtained with the boundary element method solution, where the free surface is discretized. The solution is further compared to that of a 2.5D half-space, and with experimental results available in the literature.
The asymptotic behaviour of the solution is explored for different limits of the distance, frequency and wave number, and the ensuing limits are compared to existing fundamental solutions.Peer Reviewe
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