On the Fractal Distribution of HII Regions in Disk Galaxies

In this work we quantify the degree to which star-forming events are clumped. We apply a precise and accurate technique to calculate the correlation dimension Dc of the distribution of HII regions in a sample of disk galaxies. Our reliable results are distributed in the range 1.5<Dc<2.0. We get significant variations in the fractal dimension among galaxies, contrary to a universal picture sometimes claimed in literature. The faintest galaxies tend to distribute their HII regions in more clustered (less uniform) patterns. Moreover, the fractal dimension for the brightest HII regions within the same galaxy seems to be smaller than for the faintest ones suggesting some kind of evolutionary effect.Comment: 6 pages including 4 figures. To appear in Highlights of Spanish Astrophysics V: Proceedings of the VIII Scientific Meeting of the Spanish Astronomical Society held in Santander, July 7-11, 200

Risk sharing, investment, and incentives in the neoclassical growth model

We first study growth and risk sharing in a stochastic growth model with preference shocks and two risk-averse agents. In periods in which one of the agents needs extra consumption (insurance), it is socially optimal to reduce the consumption of the other agent (redistribution) and also to accumulate fewer resources for the future (disinvestment). The latter hurts growth while the former only affects the distribution of aggregate consumption. Then, to analyze if information matters, we study if the same allocation would be implementable under private information. We find that it depends on the state of the economy. The provision of insurance that is implemented by reducing capital accumulation deteriorates the prospects of all agents in the economy and thus helps to alleviate informational frictions. The size of redistribution versus disinvestment and the outlook of economic growth at the time of disinvestment affects the possibilities of implementing the best possible allocation when the preference shock is private information. Therefore, we conjecture that under private information the best allocation compatible with incentives would tend to hurt growth and to concentrate resources in agents with private information in order to provide incentives to report the shock truthfully.Business cycles ; Economic growth

A catalogue of open cluster radii determined from Gaia proper motions

In this work we improve a previously published method to calculate in a reliable way the radius of an open cluster. The method is based on the behaviour of stars in the proper motion space as the sampling changes in the position space. Here we describe the new version of the method and show its performance and robustness. Additionally, we apply it to a large number of open clusters using data from Gaia DR2 to generate a catalogue of 401 clusters with reliable radius estimations. The range of obtained apparent radii goes from Rc=1.4+-0.1 arcmin (for the cluster FSR 1651) to Rc=25.5+-3.5 arcmin (for NGC~2437). Cluster linear sizes follow very closely a lognormal distribution with a mean characteristic radius of Rc=3.7 pc, and its high radius tail can be fitted by a power law as N \propto Rc^(-3.11+-0.35). Additionally, we find that number of members, cluster radius and age follow the relationship Nc \propto Rc^(1.2+-0.1) Tc^(-1.9+-0.4) where the younger and more extensive the cluster, the more members it presents. The proposed method is not sensitive to low density or irregular spatial distributions of stars and, therefore, is a good alternative or complementary procedure to calculate open cluster radii not having previous information on star memberships.Comment: 13 pages including 9 figures and 2 tables (main table will be available online). Accepted for publication in MNRA

NGC 2548: clumpy spatial and kinematic structure in an intermediate-age galactic cluster

NGC 2548 is a 400-500 Myr old open cluster with evidence of spatial substructures likely caused by its interaction with the Galactic disk. In this work we use precise astrometric data from the Carte du Ciel - San Fernando (CdC-SF) catalogue to study the clumpy structure in this cluster. We confirm the fragmented structure of NGC 2548 but, additionally, the relatively high precision of our kinematic data lead us to the first detection of substructures in the proper motion space of a stellar cluster. There are three spatially separated cores each of which has its own counterpart in the proper motion distribution. The two main cores lie nearly parallel to the Galactic plane whereas the third one is significantly fainter than the others and it moves toward the Galactic plane separating from the rest of the cluster. We derive core positions and proper motions, as well as the stars belonging to each core.Comment: 9 pages, 8 figures, 4 tables. Accepted for publication in MNRA

A method for determining the radius of an open cluster from stellar proper motions

We propose a method for calculating the radius of an open cluster in an objective way from an astrometric catalogue containing, at least, positions and proper motions. It uses the minimum spanning tree (hereinafter MST) in the proper motion space to discriminate cluster stars from field stars and it quantifies the strength of the cluster-field separation by means of a statistical parameter defined for the first time in this paper. This is done for a range of different sampling radii from where the cluster radius is obtained as the size at which the best cluster-field separation is achieved. The novelty of this strategy is that the cluster radius is obtained independently of how its stars are spatially distributed. We test the reliability and robustness of the method with both simulated and real data from a well-studied open cluster (NGC 188), and apply it to UCAC4 data for five other open clusters with different catalogued radius values. NGC 188, NGC 1647, NGC 6603 and Ruprecht 155 yielded unambiguous radius values of 15.2+/-1.8, 29.4+/-3.4, 4.2+/-1.7 and 7.0+/-0.3 arcmin, respectively. ASCC 19 and Collinder 471 showed more than one possible solution but it is not possible to know whether this is due to the involved uncertainties or to the presence of complex patterns in their proper motion distributions, something that could be inherent to the physical object or due to the way in which the catalogue was sampled.Comment: 12 pages including 14 figures and 1 table. Accepted for publication in MNRA

Management System for Harvest Scheduling: The Case of Horticultural Production in Southeast Spain

horticultural farmer, optimization, planning, mathematical programming, marketing, cooperative, Agribusiness, Crop Production/Industries, Demand and Price Analysis, Farm Management, Land Economics/Use,

Learning and enactive interfaces

International audienceEnactive Learning is a relatively new expression, used in enactive community, to desinate the process of learning by doing. In human sciences, several theories/models are confronted concerning the learning process