A Braneworld Universe From Colliding Bubbles

Much work has been devoted to the phenomenology and cosmology of the so-called braneworld universe, where our (3+1)-dimensional universe lies on a brane surrounded by a (4+1)-dimensional bulk spacetime that is essentially empty except for a negative cosmological constant and the various modes associated with gravity. For such a braneworld cosmology, the difficulty of justifying some preferred initial conditions inevitably arises. The various proposals for inflation restricted to the brane only partially explain the homogeneity and isotropy of the resulting braneworld universe because the homogeneity and isotropy of the bulk must be assumed. We propose a mechanism by which a brane surrounded by AdS space arises naturally so that the homogeneity and isotropy of both the brane and the bulk are guaranteed. We postulate an initial false vacuum phase of (4+1)-dimensional Minkowski or de Sitter space subsequently decaying to a true vacuum of anti-de Sitter space, assumed discretely degenerate. This decay takes place through bubble nucleation. When two bubbles of the true AdS vacuum collide, a brane (or domain wall) inevitably forms between the two AdS phases. We live on this brane. The SO(3,1) symmetry of the collision geometry ensures the three-dimensional spatial homogeneity and isotropy of the universe on the brane as well as of the bulk. In the semi-classical limit, this symmetry is exact. We sketch how the leading quantum corrections translate into cosmological perturbations.Comment: 15 pages Latex (seven ps figures). Minor revisions, references added and figures improve

DataOps for Societal Intelligence: a Data Pipeline for Labor Market Skills Extraction and Matching

Big Data analytics supported by AI algorithms can support skills localization and retrieval in the context of a labor market intelligence problem. We formulate and solve this problem through specific DataOps models, blending data sources from administrative and technical partners in several countries into cooperation, creating shared knowledge to support policy and decision-making. We then focus on the critical task of skills extraction from resumes and vacancies featuring state-of-the-art machine learning models. We showcase preliminary results with applied machine learning on real data from the employment agencies of the Netherlands and the Flemish region in Belgium. The final goal is to match these skills to standard ontologies of skills, jobs and occupations

Assessing Web Services Interfaces with Lightweight Semantic Basis

In the last years, Web Services have become the technological choice to materialize the Service-Oriented Computing paradigm. However, a broad use of Web Services requires efficient approaches to allow service consumption from within applications. Currently, developers are compelled to search for suitable services mainly by manually exploring Web catalogs, which usually show poorly relevant information, than to provide the adequate "glue-code" for their assembly. This implies a large effort into discovering, selecting and adapting services. To overcome these challenges, this paper presents a novel Web Service Selection Method. We have defined an Interface Compatibility procedure to assess structural-semantic aspects from functional specifications - in the form of WSDL documents - of candidate Web Services. Two different semantic basis have been used to define and implement the approach: WordNet, a widely known lexical dictionary of the English language; and DISCO, a database which indexes co-occurrences of terms in very large text collections. We performed a set of experiments to evaluate the approach regarding the underlying semantic basis and against third-party approaches with a data-set of real-life Web Services. Promising results have been obtained in terms of well-known metrics of the Information Retrieval field

Cosmological Perturbations Generated in the Colliding Bubble Braneworld Universe

We compute the cosmological perturbations generated in the colliding bubble braneworld universe in which bubbles filled with five-dimensional anti-de Sitter space (AdS5)expanding within a five dimensional de Sitter space (dS5) or Minkowski space (M5) collide to form a (3+1) dimensional local brane on which the cosmology is virtually identical to that of the Randall-Sundrum model. The perturbation calculation presented here is valid to linear order but treats the fluctuations of the expanding bubbles as (3+1) dimensional fields localized on the bubble wall. We find that for bubbles expanding in dS5 the dominant contribution to the power spectrum is `red' but very small except in certain cases where the fifth dimension is not large or the bubbles have expanded to far beyond the dS5 apparent horizon length. This paper supersedes a previous version titled "Exactly Scale-Invariant Cosmological Perturbations From a Colliding Bubble Braneworld Universe" in which we erroneously claimed that a scale-invariant spectrum results for the case of bubbles expanding in M5. This present paper corrects the errors of the previous version and extends the analysis to the more interesting and general case of bubbles expanding in dS5.Comment: 29 pages Latex with eps figures. Major errors in the original version of the paper corrected and analysis extended to bubbles expanding in dS

Aumentando el acceso y la compleción a la educación superior: ¿Cuánto puede ayudar la educación gratuita?

Las propuestas sobre educación universitarias gratuita se han vuelto cada vez más populares en muchos países del mundo. Para evaluar sus efectos potenciales, desarrollamos y estimamos un modelo dinámico de matrícula, desempeño y graduación universitaria. Una pieza central del modelo, el esfuerzo de los estudiantes, tiene un efecto directo sobre el desempeño y un efecto indirecto en la mitigación del riesgo asociado. Estimamos el modelo utilizando datos a nivel de estudiantes en Colombia, y usamos las estimaciones para simular programas de universidad gratuita que difieren en requisitos de elegibilidad. Entre estos, el programa sin requisitos es el que más expande la inscripción, pero no afecta las tasas de graduación y tiene el costo más alto. El programa basado en rendimiento, por el contrario, ofrece una expansión de matrícula ligeramente menor pero una mayor tasa de graduación a un costo más bajo. En relación con el programa sin requisitos, aquel basado en rendimiento supone un mayor riesgo para los estudiantes, pero es precisamente esta la razón de los mejores resultados. No obstante, el modesto aumento en las tasas de graduación sugiere que podrían ser necesarias políticas complementarias adicionales para incentivar el esfuerzo necesario para aumentar las tasas de graduación.Free college proposals have become increasingly popular in many countries of the world. To evaluate their potential effects, we develop and estimate a dynamic model of college enrollment, performance, and graduation. A central piece of the model, student effort, has a direct effect on class completion, and an indirect effect in mitigating the risk of not completing a class or not remaining in college. We estimate the model using rich, student-level administrative data from Colombia, and use the estimates to simulate free college programs that differ in eligibility requirements. Among these, universal free college expands enrollment the most, but it does not affect graduation rates and has the highest per-graduate cost. Performance-based free college, in contrast, delivers a slightly lower enrollment expansion yet a greater graduation rate at a lower per-graduate cost. Relative to universal free college, performance-based free college places a greater risk on students but is precisely this feature that delivers better outcomes. Nonetheless, the modest increase in graduation rates suggests that additional, complementary policies might be required to elicit the large effort increase needed to raise graduation rates.Enfoque En las economías modernas, la educación superior juega un papel crucial en la formación de capital humano calificado. La educación superior no solo puede aumentar la productividad de un país; también puede reducir la desigualdad de ingresos. Al subsidiar el acceso a la educación superior, los hacedores de política pueden contribuir a mejorar estos dos aspectos. La pregunta es ¿qué tan grande es la subvención que se debería proporcionar? Los defensores del concepto de educación universitaria gratuita argumentan que los hacedores de política deberían proporcionar un subsidio completo, lo que resulta en una matrícula con costo cero para los estudiantes. Para investigar los efectos potenciales de la universidad gratuita, desarrollamos un modelo dinámico de matrícula, desempeño y graduación universitaria. En el modelo, un estudiante universitario enfrenta riesgos que pueden impedirle completar una clase o permanecer en la universidad. A través de su esfuerzo, el estudiante puede mitigar estos riesgos y afectar su propio desempeño, completando más clases hasta alcanzar un nivel mínimo para graduarse. De esta forma, el modelo sugiere que para afectar las tasas de graduación, una política debe inducir un aumento en el esfuerzo de los estudiantes. Contribución Este estudio se relaciona con una amplia literatura que estima modelos de educación secuencial bajo incertidumbre. Al igual que en estos artículos, los estudiantes de nuestro modelo aprenden sobre su probabilidad de graduación en función de sus clases completadas y eligen el esfuerzo en consecuencia. Sin embargo, la mayoría se ha enfocado principalmente en el rol de la habilidad exógena del estudiante y no tanto así en el papel del esfuerzo. Nuestra principal contribución en esta línea de investigación es la inclusión explícita del esfuerzo como la variable de decisión endógena, la cual determina la acumulación de clases y la mitigación de riesgos en un entorno dinámico. Asimismo, el modelo estimado permite generar predicciones que permiten analizar el comportamiento del esfuerzo en escenarios contrafactuales y las implicaciones que este puede tener sobre variables de interés relacionadas con matrícula, graduación, deserción y progresión académica. Resultados Usamos el modelo estimado para simular programas de universidad gratuita que difieren en requisitos de elegibilidad. Frente al escenario base, todos los programas aumentan la matrícula en un 70-85%. Entre estos, el programa sin requisitos es el que más expande las tasas matrícula, pero sin afectar las tasas de graduación y tiene con el costo por graduado más alto. El programa basado en rendimiento, por el contrario, ofrece una expansión de las tasas matrícula ligeramente menor pero con tasas de graduación 9-14% más altas y a un costo por graduado más bajo. Esto implica que subsidiar la educación superior mediante un programa de universidad gratuita, si bien aumenta substancialmente las tasas de matrícula, no tiene un efecto considerable sobre el esfuerzo de los estudiantes, lo cual implica un aumento moderado o inexistente en la progresión académica promedio y en las tasas de graduación. Lo anterior sugiere la necesidad de políticas complementarias dirigidas a incentivar cambios en el esfuerzo suficientemente altos de forma que se logren aumentos considerables en la progresión académica y las tasas de graduación. FRASE DESTACADA El modelo estimado permite generar predicciones que permiten analizar el comportamiento del esfuerzo en escenarios contrafactuales y las implicaciones que este puede tener sobre variables de interés relacionadas con matrícula, graduación, deserción y progresión académica

Isolated Minkowski vacua, and stability analysis for an extended brane in the rugby ball

We study a recently proposed model, where a codimension one brane is wrapped around the axis of symmetry of an internal two dimensional space compactified by a flux. This construction is free from the problems which plague delta-like, codimension two branes, where only tension can be present. In contrast, arbitrary fields can be localized on this extended brane, and their gravitational interaction is standard 4d gravity at large distance. In the first part of this note, we study the de Sitter (dS) vacua of the model. The landscape of these vacua is characterized by discrete points labeled by two integer numbers, related to the flux responsible for the compactification and to the current of a brane field. A Minkowski external space emerges only for a special ratio between these two integers, and it is therefore (topologically) isolated from the nearby dS solutions. In the second part, we show that the Minkowski vacua are stable under the most generic axially-symmetric perturbations (we argue that this is sufficient to ensure the overall stability).Comment: 12 pages, 4 .eps figure

Probabilities in the inflationary multiverse

Inflationary cosmology leads to the picture of a "multiverse," involving an infinite number of (spatially infinite) post-inflationary thermalized regions, called pocket universes. In the context of theories with many vacua, such as the landscape of string theory, the effective constants of Nature are randomized by quantum processes during inflation. We discuss an analytic estimate for the volume distribution of the constants within each pocket universe. This is based on the conjecture that the field distribution is approximately ergodic in the diffusion regime, when the dynamics of the fields is dominated by quantum fluctuations (rather than by the classical drift). We then propose a method for determining the relative abundances of different types of pocket universes. Both ingredients are combined into an expression for the distribution of the constants in pocket universes of all types.Comment: 18 pages, RevTeX 4, 2 figures. Discussion of the full probability in Sec.VI is sharpened; the conclusions are strengthened. Note added explaining the relation to recent work by Easther, Lim and Martin. Some references adde

Blockchain and Cryptocurrencies: a Classification and Comparison of Architecture Drivers

Blockchain is a decentralized transaction and data management solution, the technological leap behind the success of Bitcoin and other cryptocurrencies. As the variety of existing blockchains and distributed ledgers continues to increase, adopters should focus on selecting the solution that best fits their needs and the requirements of their decentralized applications, rather than developing yet another blockchain from scratch. In this paper we present a conceptual framework to aid software architects, developers, and decision makers to adopt the right blockchain technology. The framework exposes the interrelation between technological decisions and architectural features, capturing the knowledge from existing academic literature, industrial products, technical forums/blogs, and experts' feedback. We empirically show the applicability of our framework by dissecting the platforms behind Bitcoin and other top 10 cryptocurrencies, aided by a focus group with researchers and industry practitioners. Then, we leverage the framework together with key notions of the Architectural Tradeoff Analysis Method (ATAM) to analyze four real-world blockchain case studies from industry and academia. Results shown that applying our framework leads to a deeper understanding of the architectural tradeoffs, allowing to assess technologies more objectively and select the one that best fit developers needs, ultimately cutting costs, reducing time-to-market and accelerating return on investment.Comment: Accepted for publication at journal Concurrency and Computation: Practice and Experience. Special Issue on distributed large scale applications and environment

DevOps and Quality Management in Serverless Computing: The RADON Approach

The onset of microservices and serverless computer solutions has forced an ever-increasing demand for tools and techniques to establish and maintain the quality of infrastructure code, the blueprint that drives the operationalization of large-scale software systems. In the EU H2020 project RADON, we propose a machine-learning approach to elaborate and evolve Infrastructure-as-Code as part of a full-fledged industrial-strength DevOps pipeline. This paper illustrates RADON and shows our research roadmap