Core instability models of giant planet accretion II: forming planetary systems

We develop a simple model for computing planetary formation based on the core instability model for the gas accretion and the oligarchic growth regime for the accretion of the solid core. In this model several planets can form simultaneously in the disc, a fact that has important implications specially for the changes in the dynamic of the planetesimals and the growth of the cores since we consider the collision between them as a source of potential growth. The type I and II migration of the embryos and the migration of the planetesimals due to the interaction with the disc of gas are also taken into account. With this model we consider different initial conditions to generate a variety of planetary systems and analyse them statistically. We explore the effects of using different type I migration rates on the final number of planets formed per planetary system such as on the distribution of masses and semimajor axis of extrasolar planets, where we also analyse the implications of considering different gas accretion rates. A particularly interesting result is the generation of a larger population of habitable planets when the gas accretion rate and type I migration are slower.Comment: 4 figures and 1 table. Accepted for publication in MNRA

Anomalous Nonlocal Resistance and Spin-charge Conversion Mechanisms in Two-Dimensional Metals

We uncover two anomalous features in the nonlocal transport behavior of two-dimensional metallic materials with spin-orbit coupling. Firstly, the nonlocal resistance can have negative values and oscillate with distance, even in the absence of a magnetic field. Secondly, the oscillations of the nonlocal resistance under an applied in-plane magnetic field (Hanle effect) can be asymmetric under field reversal. Both features are produced by direct magnetoelectric coupling, which is possible in materials with broken inversion symmetry but was not included in previous spin diffusion theories of nonlocal transport. These effects can be used to identify the relative contributions of different spin-charge conversion mechanisms. They should be observable in adatom-functionalized graphene, and may provide the reason for discrepancies in recent nonlocal transport experiments on graphene.Comment: 5 pages, 3 figures, and Supplementary Materials, to appear in Phys. Rev. Let

Geometric phases in 2D and 3D polarized fields: geometrical, dynamical, and topological aspects

Geometric phases are a universal concept that underpins numerous phenomena involving multi-component wave fields. These polarization-dependent phases are inherent in interference effects, spin-orbit interaction phenomena, and topological properties of vector wave fields. Geometric phases have been thoroughly studied in two-component fields, such as two-level quantum systems or paraxial optical waves. However, their description for fields with three or more components, such as generic nonparaxial optical fields routinely used in modern nano-optics, constitutes a nontrivial problem. Here we describe geometric, dynamical, and total phases calculated along a closed spatial contour in a multi-component complex field, with particular emphasis on 2D (paraxial) and 3D (nonparaxial) optical fields. We present several equivalent approaches: (i) an algebraic formalism, universal for any multi-component field; (ii) a dynamical approach using the Coriolis coupling between the spin angular momentum and reference-frame rotations; and (iii) a geometric representation, which unifies the Pancharatnam-Berry phase for the 2D polarization on the Poincar\'e sphere and the Majorana-sphere representation for the 3D polarized fields. Most importantly, we reveal close connections between geometric phases, angular-momentum properties of the field, and topological properties of polarization singularities in 2D and 3D fields, such as C-points and polarization M\"obius strips.Comment: 21 pages, 11 figures, to appear in Rep. Prog. Phy

The Central Role of Noise in Evaluating Interventions that Use Test Scores to Rank Schools

Several countries have implemented programs that use test scores to rank schools, and to reward or penalize them based on their students' average performance. Recently, Kane and Staiger (2002) have warned that imprecision in the measurement of school-level test scores could impede these efforts. There is little evidence, however, on how seriously noise hinders the evaluation of the impact of these interventions. We examine these issues in the context of Chile's P-900 program a country-wide intervention in which resources were allocated based on cutoffs in schools' mean test scores. We show that transitory noise in average scores and mean reversion lead conventional estimation approaches to greatly overstate the impacts of such programs. We then show how a regression discontinuity design that utilizes the discrete nature of the selection rule can be used to control for reversion biases. While the RD analysis provides convincing evidence that the P-900 program had significant effects on test score gains, these effects are much smaller than is widely believed.

Phase Synchronization and Polarization Ordering of Globally-Coupled Oscillators

We introduce a prototype model for globally-coupled oscillators in which each element is given an oscillation frequency and a preferential oscillation direction (polarization), both randomly distributed. We found two collective transitions: to phase synchronization and to polarization ordering. Introducing a global-phase and a polarization order parameters, we show that the transition to global-phase synchrony is found when the coupling overcomes a critical value and that polarization order enhancement can not take place before global-phase synchrony. We develop a self-consistent theory to determine both order parameters in good agreement with numerical results

Objective Competitiveness Ranking amongst EU Regions (Objective Method for Quantifying Regional Competitiveness - a case study applied to EU15 Regions)

Nowadays the key target of Cohesion Policy is to promote the creation of conditions to improve the growth, and to increase the factors that lead to a real convergence (Economic and Social Cohesion). An important group of these factors is found when considering the competitivity of a Region that implies, (even whitout existintg a clear definition), to consider at the same time two different levels: - The first one through the specific factors to improve the development of the resident managerial weave (Innovation, Research & Development, enterprises nets, labour market, training, support in the use of new technologies, servicies to entreprises, etc.). – The second one, improving the enviromental conditions for the development of such an managerial activity (Transport and comunication infrastructures, environment and sustainable developpment ,use of renewable energies, etc.) The objetcive of the present paper is to propose an objective way to consider the totalitiy of factors simultaneously, in order to obtain a ranking of the of the regional competitivity, and to study his changes in the time. For this, it will be used the data base “REGIO” and techniques of ranking belonging to multicriteria decision making. The analyzed period is from 1987 to 2002 which shows interesting results mainly when compared with other analyses carried out.

Reseña de "Historia del estudio de la administración pública en México" de José Juan Sánchez González

Inicio por decir que en los últimos tiempos José Juan Sánchez González se ha destacado por ser uno de los autores que cuentan con más obra derivada de la investigación de administración pública en México. Por eso se presenta a los lectores una obra fundamental, en virtud de que recupera no sólo el desarrollo histórico de la administración pública en México del siglo XIX, sino que profundiza su estudio al siglo XX y además proyecta su obra a los últimos trabajos realizados en esta disciplina en el siglo XXI

El capital social y el valor público como ejes de acción para el desarrollo social

El propósito del presente ensayo es describir las teorías capital social y valor público en tanto teorías que son susceptibles de estar integradas bajo la idea de explicación de lo que pude ser recuperado de las organizaciones civiles, a fin de ser éstas las representantes de la sociedad en general para conjugar con el gobierno y su administración pública, políticas públicas acordes a las necesidades de la sociedad, además de que el propio gobierno desde la óptica del valor público no sólo debe conformarse con realizar sus funciones con eficiencia, sino buscar además, esquemas que posibiliten una mejor forma de satisfacer las demandas de la sociedad de manera directa y en términos complementarios generar innovaciones que produzcan un nuevo valor público para el beneficio de la comunidad, así de esta forma, tanto el capital social como el valor público se constituyen como teorías innovadoras para hacer que la sociedad organizada participe con los gobiernos para lograr mejores condiciones de vida y éstos actúen para satisfacer las demandas de la sociedad bajo esquemas de índole estratégico que redundarán en la obtención de los resultados planeados, mediante la participación social.El propósito del presente ensayo es describir las teorías capital social y valor público en tanto teorías que son susceptibles de estar integradas bajo la idea de explicación de lo que pude ser recuperado de las organizaciones civiles, a fin de ser éstas las representantes de la sociedad en general para conjugar con el gobierno y su administración pública, políticas públicas acordes a las necesidades de la sociedad, además de que el propio gobierno desde la óptica del valor público no sólo debe conformarse con realizar sus funciones con eficiencia, sino buscar además, esquemas que posibiliten una mejor forma de satisfacer las demandas de la sociedad de manera directa y en términos complementarios generar innovaciones que produzcan un nuevo valor público para el beneficio de la comunidad, así de esta forma, tanto el capital social como el valor público se constituyen como teorías innovadoras para hacer que la sociedad organizada participe con los gobiernos para lograr mejores condiciones de vida y éstos actúen para satisfacer las demandas de la sociedad bajo esquemas de índole estratégico que redundarán en la obtención de los resultados planeados, mediante la participación social