Meeting the millennium development goal in education : a cost-effectiveness analysis for Ecuador

Ecuador;education;development strategy;input output analysis;primary education;secondary education

Towards predictive many-body calculations of phonon-limited carrier mobilities in semiconductors

We probe the accuracy limit of {\it ab initio} calculations of carrier mobilities in semiconductors, within the framework of the Boltzmann transport equation. By focusing on the paradigmatic case of silicon, we show that fully predictive calculations of electron and hole mobilities require many-body quasiparticle corrections to band structures and electron-phonon matrix elements, the inclusion of spin-orbit coupling, and an extremely fine sampling of inelastic scattering processes in momentum space. By considering all these factors we obtain excellent agreement with experiment, and we identify the band effective masses as the most critical parameters to achieve predictive accuracy. Our findings set a blueprint for future calculations of carrier mobilities, and pave the way to engineering transport properties in semiconductors by design.Comment: 11 pages and 8 figure

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

Exterior spacetime for stellar models in 5-dimensional Kaluza-Klein gravity

It is well-known that Birkhoff's theorem is no longer valid in theories with more than four dimensions. Thus, in these theories the effective 4-dimensional picture allows the existence of different possible, non-Schwarzschild, scenarios for the description of the spacetime outside of a spherical star, contrary to general relativity in 4D. We investigate the exterior spacetime of a spherically symmetric star in the context of Kaluza-Klein gravity. We take a well-known family of static spherically symmetric solutions of the Einstein equations in an empty five-dimensional universe, and analyze possible stellar exteriors that are conformal to the metric induced on four-dimensional hypersurfaces orthogonal to the extra dimension. All these exteriors are continuously matched with the interior of the star. Then, without making any assumptions about the interior solution, we prove the following statement: the condition that in the weak-field limit we recover the usual Newtonian physics singles out an unique exterior. This exterior is "similar" to Scharzschild vacuum in the sense that it has no effect on gravitational interactions. However, it is more realistic because instead of being absolutely empty, it is consistent with the existence of quantum zero-point fields. We also examine the question of how would the deviation from the Schwarzschild vacuum exterior affect the parameters of a neutron star. In the context of a model star of uniform density, we show that the general relativity upper limit M/R < 4/9 is significantly increased as we go away from the Schwarzschild vacuum exterior. We find that, in principle, the compactness limit of a star can be larger than 1/2, without being a black hole. The generality of our approach is also discussed.Comment: Typos corrected. Accepted for publication in Classical and Quantum Gravit

Hydrostatic Equilibrium of a Perfect Fluid Sphere with Exterior Higher-Dimensional Schwarzschild Spacetime

We discuss the question of how the number of dimensions of space and time can influence the equilibrium configurations of stars. We find that dimensionality does increase the effect of mass but not the contribution of the pressure, which is the same in any dimension. In the presence of a (positive) cosmological constant the condition of hydrostatic equilibrium imposes a lower limit on mass and matter density. We show how this limit depends on the number of dimensions and suggest that $\Lambda > 0$ is more effective in 4D than in higher dimensions. We obtain a general limit for the degree of compactification (gravitational potential on the boundary) of perfect fluid stars in $D$-dimensions. We argue that the effects of gravity are stronger in 4D than in any other number of dimensions. The generality of the results is also discussed

Stellar models with Schwarzschild and non-Schwarzschild vacuum exteriors

A striking characteristic of non-Schwarzschild vacuum exteriors is that they contain not only the total gravitational mass of the source, but also an {\it arbitrary} constant. In this work, we show that the constants appearing in the "temporal Schwarzschild", "spatial Schwarzschild" and "Reissner-Nordstr{\"o}m-like" exteriors are not arbitrary but are completely determined by star's parameters, like the equation of state and the gravitational potential. Consequently, in the braneworld scenario the gravitational field outside of a star is no longer determined by the total mass alone, but also depends on the details of the internal structure of the source. We show that the general relativistic upper bound on the gravitational potential $M/R < 4/9$, for perfect fluid stars, is significantly increased in these exteriors. Namely, $M/R < 1/2$, $M/R < 2/3$ and $M/R < 1$ for the temporal Schwarzschild, spatial Schwarzschild and Reissner-Nordstr{\"o}m-like exteriors, respectively. Regarding the surface gravitational redshift, we find that the general relativistic Schwarzschild exterior as well as the braneworld spatial Schwarzschild exterior lead to the same upper bound, viz., $Z < 2$. However, when the external spacetime is the temporal Schwarzschild metric or the Reissner-Nordstr{\"o}m-like exterior there is no such constraint: $Z < \infty$. This infinite difference in the limiting value of $Z$ is because for these exteriors the effective pressure at the surface is negative. The results of our work are potentially observable and can be used to test the theory.Comment: 19 pages, 3 figures and caption

Multidimensional Marine Data: The next frontier for Hydrographic Offices

Hydrographic offices today exist in a world of accelerating technological change that is influencing human behavior, creating new needs and ways for exploiting data to understand our world. Hydrographic offices have traditionally been the producers of nautical information for safety of navigation. By the end of the 20th century, with the appearance of the IHO S-57 Standard, their main challenge was to evolve into a central database production system. Now, the main challenge and opportunity is to evolve from there into a true geospatial agency, developing a hydrospatial information system capable of providing products and services for multidimensional analysis and decision-making through apps and web browsers at the "speed of trust." The technology to do this is there; it is a matter of vision and desire to move toward the next frontier.Los Servicios Hidrográficos existen hoy en día en un mundo de cambios tecnológicos acelerados que están influyendo en el comportamiento humano, creando nuevas necesidades y formas de explotar los datos para entender nuestro mundo. Los Servicios Hidrográficos han sido tradicionalmente los productores de información náutica para la seguridad de la navegación. A finales del siglo XX, con la aparición de la Norma S-57 de la OHI, su principal desafío fue evolucionar hacia un sistema central de producción de bases de datos. Ahora, el desafío y la oportunidad principales son evolucionar hacia una verdadera agencia geoespacial, desarrollando un sistema de información hidroespacial capaz de proporcionar productos y servicios para un análisis y una toma de decisiones multidimensionales mediante aplicaciones y navegadores web a la "velocidad de la confianza". La tecnología para hacerlo está ahí; es una cuestión de visión y de deseo de avanzar hacia la próxima frontera.Les services hydrographiques évoluent aujourd’hui dans un monde où les changements technologiques s’accélèrent, influençant le comportement humain, créant de nouveaux besoins et de nouvelles manières d’exploiter les données afin de comprendre notre monde. Les services hydrographiques sont les traditionnels producteurs des informations nautiques aux fins de la sécurité de la navigation. A la fin du 20ème siècle, avec l’apparition de la norme S-57 de l’OHI, leur principal défi était d’évoluer pour devenir un système central de production de base de données. A présent, leur principal défi et opportunité est d’évoluer de ce rôle pour devenir une véritable agence géospatiale, en développant un système d’informations hydrospatiales capable de fournir des produits et services aux fins d’analyse multidimensionnelle et de prise de décision via des applications et des navigateurs web à la « vitesse de la confiance ». La technologie pour relever ce défi existe, c’est donc une question de vision et de volonté d’avancer vers la prochaine frontière

Brane classical and quantum cosmology from an effective action

Motivated by the Randall-Sundrum brane-world scenario, we discuss the classical and quantum dynamics of a (d+1)-dimensional boundary wall between a pair of (d+2)-dimensional topological Schwarzschild-AdS black holes. We assume there are quite general -- but not completely arbitrary -- matter fields living on the boundary ``brane universe'' and its geometry is that of an Friedmann-Lemaitre-Robertson-Walker (FLRW) model. The effective action governing the model in the mini-superspace approximation is derived. We find that the presence of black hole horizons in the bulk gives rise to a complex action for certain classically allowed brane configurations, but that the imaginary contribution plays no role in the equations of motion. Classical and instanton brane trajectories are examined in general and for special cases, and we find a subset of configuration space that is not allowed at the classical or semi-classical level; these correspond to spacelike branes carrying tachyonic matter. The Hamiltonization and Dirac quantization of the model is then performed for the general case; the latter involves the manipulation of the Hamiltonian constraint before it is transformed into an operator that annihilates physical state vectors. The ensuing covariant Wheeler-DeWitt equation is examined at the semi-classical level, and we consider the possible localization of the brane universe's wavefunction away from the cosmological singularity. This is easier to achieve for branes with low density and/or spherical spatial sections.Comment: Shortened to match version accepted by Phys. Rev. D (unabridged text found in version 2), 42 pages, 9 figures, Rextex