Effective dynamics of the hybrid quantization of the Gowdy T^3 universe

The quantum dynamics of the linearly polarized Gowdy T^3 model (compact inhomogeneous universes admitting linearly polarized gravitational waves) is analyzed within Loop Quantum Cosmology by means of an effective dynamics. The analysis, performed via analytical and numerical methods, proves that the behavior found in the evolution of vacuum (homogeneous) Bianchi I universes is preserved qualitatively also in the presence of inhomogeneities. More precisely, the initial singularity is replaced by a big bounce which joins deterministically two large classical universes. In addition, we show that the size of the universe at the bounce is at least of the same order of magnitude (roughly speaking) as the size of the corresponding homogeneous universe obtained in the absence of gravitational waves. In particular, a precise lower bound for the ratio of these two sizes is found. Finally, the comparison of the amplitudes of the gravitational wave modes in the distant future and past shows that, statistically (i.e., for large samples of universes), the difference in amplitude is enhanced for nearly homogeneous universes, whereas this difference vanishes in inhomogeneity dominated cases. The presented analysis constitutes the first systematic effective study of an inhomogeneous system within Loop Quantum Cosmology, and it proves the robustness of the results obtained for homogeneous cosmologies in this context.Comment: 21 pages, 11 figures, RevTex4-1 + BibTe

Uso de ODR en las comunidades de desarrollo de software libre

La revolució del programari lliure ha estat i és un dels fenòmens més imprevisibles i de major abast que han sorgit des del desenvolupament de les Tecnologies de la Informació. No obstant això és un fenomen que, a causa de pròpia construcció social i distribuïda, està intrínsecament unit a la noció de conflicte, la manifestació del qual més notòria és la bifurcació o fork. En el present treball analitzem els diferents tipus de conflictes i els mecanismes habitualment emprats per a la resolució dels mateixos, i si formen part dels denominats mètodes alternatius de resolució de controvèrsies en Línia o ODR o si són part d'una categoria diferent i separada.La revolución del software libre ha sido y es uno de los fenómenos más imprevisibles y de mayor alcance que han surgido desde el desarrollo de las Tecnologías de la Información. Sin embargo es un fenómeno que, debido a propia construcción social y distribuida, está intrínsecamente unido a la noción de conflicto, cuya manifestación más notoria es la bifurcación o fork. En el presente trabajo analizamos los distintos tipos de conflictos y los mecanismos habitualmente empleados para la resolución de los mismos, y si forman parte de los denominados métodos alternativos de resolución de controversias en Línea u ODR o si son parte de una categoría distinta y separada.The free software revolution has been and is one of the most unpredictable and far-reaching that has emerged since the development of Information Technology. However, it is a phenomenon that, due to social construction and distributed, is intrinsically linked to the notion of conflict, the most prominent features is the bifurcation or fork. In this paper we analyze the different types of conflicts and the mechanisms normally used to solve them, and they are part of the so-called alternative dispute resolution, or ODR Online or are part of a distinct and separate

The subversive nature of Beloved’s Sethe Suggs, the “iron-eyed” woman

Treballs Finals del Grau d'Estudis Anglesos, Facultat de Filologia, Universitat de Barcelona, Curs: 2019-2020, Tutora: Cristina Alsina Rísquez[eng] Toni Morrison’s Beloved is a novel that gives voice to those thousands of Black women whose stories have often been erased from the history of American slavery and, thus, proves to be not only one of the most relevant works in African-American women’s writing, but also a pivotal piece in contemporary literature. In her novel, Morrison presents the story of Sethe Suggs, a woman who is determined to claim freedom and control over her life in a time and place in which such a thing was not allowed for Black women. This paper will provide an analysis of said character in relation to slavery, motherhood and stereotypical images of African-American women with the purpose of illustrating her subversive nature.[cat] Beloved de l’autora Toni Morrison és una novel·la que dona veu a totes aquelles dones negres que sovint han sigut esborrades de la història de l’esclavitud a Amèrica, demostrant ser així no només una de les obres més importants en l’àmbit de l’escriptura de dones d’ascendència Afro-Americana, sinó també una peça essencial de la literatura contemporània. En aquesta novel·la, Morrison presenta la història de Sethe Suggs, una dona que està decidida a exigir la seva llibertat i el control sobre la seva vida en un moment i un lloc en el qual aquests drets no estaven a l’abast de les dones Afro-Americanes. Amb el propòsit de demostrar la seva naturalesa subversiva, aquest treball presentarà un anàlisis sobre el personatge de la Sethe en relació a l’esclavitud, la maternitat i certes imatges estereotípiques de la dona Afro-Americana

Energy Assessment of Pastoral Dairy Goat Husbandry from an Agroecological Economics Perspective. A Case Study in Andalusia (Spain)

This paper presents a methodological proposal of new energy sustainability indicators according to a novel accounting that follows agroecological and ecological economics criteria. Energy output is reformulated to include manure and thus consider the contribution to fertilization made by pastoral livestock farming to agroecosystems. Energy inputs calculations include the grazing resources. These new definitions and calculations allow for new formulations of the energy return on investment (EROI) as measures of the energy efficiency of livestock farming systems (final EROI and food/feed EROI). The environmental benefit of manure is estimated from the avoided energy cost of using this alternative to inorganic fertilizers (AECM). The environmental benefit of grazing is measured through the energy cost of avoiding cultivated animal feed (AECP) and its impact in terms of non-utilized agricultural area (ALCP). The comparative analysis of different livestock breeding systems in three pastoral dairy goat farms in the Sierra de Cádiz in Andalusia, southern Spain, reveals the analytical potential of the new energy sustainability indicators proposed, as well as the potential environmental benefits derived from territorial-based stockbreeding and, more specifically, grazing activities. Those benefits include gains in energy efficiency, a reduction of the dependence on non-renewable energy, and environmental costs avoided in terms of energy in extensive pastoral systems

High-order gauge-invariant perturbations of a spherical spacetime

We complete the formulation of a general framework for the analysis of high-order nonspherical perturbations of a four-dimensional spherical spacetime by including a gauge-invariant description of the perturbations. We present a general algorithm to construct these invariants and provide explicit formulas for the case of second-order metric perturbations. We show that the well-known problem of lack of invariance for the first-order perturbations with l=0,1 propagates to increasing values of l for perturbations of higher order, owing to mode coupling. We also discuss in which circumstances it is possible to construct the invariants

Logics and orientations of digital activism. Froom use and appropriation to the development of autonomous tools

Proyecto “Sostenibilidad del Tercer Sector de la Comunicación. Diseño y Aplicación de Indicadores” (SOScom) PID2020-113011RB-I00, Financiado por MCIN/ AEIN/ 10.13039/50110001103.Introducción: A partir de la revisión teórica el presente artículo distingue dos lógicas diferenciadas que van desde el uso por parte de los activistas de herramientas comerciales al desarrollo de tecnologías autónomas impulsadas por los propios movimientos. Objetivos: El objetivo del texto es definir distintas orientaciones del activismo digital a partir de contribuciones que nos permiten reconocer lógicas de acción diferenciadas en torno a la relación entre movimientos sociales y tecnologías digitales. Se analiza críticamente dichas aportaciones y las contrastamos con la realidad empírica para cuestionar y complejizar las nociones de partida, señalando contradicciones o usos complementarios que trascienden etapas y cuestionan la lógica bipolar o evolucionista que a veces se perfila en otros enfoques. Conclusiones: Las conclusiones apuntan a una multidimensionalidad de factores que inciden en las formas en que los movimientos usan la tecnología: prácticos o utilitaristas, estratégicos y tácticos, e ideológicos o identitarios.Introduction: The text departs from a theoretical review in order to distinguish two specific dynamics involving the use of commercial tools by activists on the one hand, and the development of autonomous technologies driven by social movements themselves on the other. Objectives: The aim of this article is to define various logics of digital activism by engaging critically with several scholar contributions that, generally through a historical analysis, allow us to establish theoretical distinctions and recognize differentiated logics of action when it comes to determining how social movements actually use digital technology. In the paper, critical engagement with the literature is examined against our empirical findings to challenge pre-existing assumptions, as well as evolutionary approaches sometimes observed in some of these contributions. The text also makes a point of transcending closed historical stages. Conclusions: The article’s conclusions point towards a multidimensionality of factors (pragmatic-utilitarian, strategic-tactical and ideological/identity-related) regulating the ways in which social movement leverage technology.Ministerio de Ciencia e Innovación (MICIN) MCIN/AEI/10.13039/5011000110

Estudi numèric dels Shock filters

[cat] Un dels objectius de la informàtica és proporcionar-nos eines per a simplificar la nostra vida quotidiana. Un dels problemes que ha de resoldre és el tractament d’imatges: Per exemple, un fons que, amb el pas del temps, s’han deteriorat i volem recuperar part de la informació, o que les nostres càmeres digitals arreglin els desperfectes que es produeixen a la fotografia per la nostra inexperiència en el maneig d’aquesta eina. Aquests són alguns dels usos que l’informàtica resol i que a les seves solucions es trobes unes eines matemàtiques consolidades

Ús de corbes el·líptiques en la criptografia i SAGE

[cat] El desenvolupament d’internet ha fet que les nostres comunicacions es realitzin mitjançant aquesta xarxa, la criptografia ens proporciona eines perquè la nostra informació es pugui transmetre de manera segura per aquesta xarxa pública. En aquest treball farem una implementació utilitzant SAGE per a utilitzar corbes el·líptiques dins la criptografia de clau pública

Big Bounce and inhomogeneities

The dynamics of an inhomogeneous universe is studied with the methods of Loop Quantum Cosmology as an example of the quantization of vacuum cosmological spacetimes containing gravitational waves (Gowdy spacetimes). The analysis performed at the effective level shows that: (i) The initial Big Bang singularity is replaced (as in the case of homogeneous cosmological models) by a Big Bounce, joining deterministically two large universes, (ii) the universe size at the bounce is at least of the same order of magnitude as that of the background homogeneous universe, (iii) for each gravitational wave mode, the difference in amplitude at very early and very late times has a vanishing statistical average when the bounce dynamics is strongly dominated by the inhomogeneities, whereas this average is positive when the dynamics is in a near-vacuum regime, so that statistically the inhomogeneities are amplified.Comment: RevTex4, 4 pages, 2 figure

Learning Latent Permutations with Gumbel-Sinkhorn Networks

Permutations and matchings are core building blocks in a variety of latent variable models, as they allow us to align, canonicalize, and sort data. Learning in such models is difficult, however, because exact marginalization over these combinatorial objects is intractable. In response, this paper introduces a collection of new methods for end-to-end learning in such models that approximate discrete maximum-weight matching using the continuous Sinkhorn operator. Sinkhorn iteration is attractive because it functions as a simple, easy-to-implement analog of the softmax operator. With this, we can define the Gumbel-Sinkhorn method, an extension of the Gumbel-Softmax method (Jang et al. 2016, Maddison2016 et al. 2016) to distributions over latent matchings. We demonstrate the effectiveness of our method by outperforming competitive baselines on a range of qualitatively different tasks: sorting numbers, solving jigsaw puzzles, and identifying neural signals in worms