Quantum diffusion beyond slow-roll: implications for primordial black-hole production

Primordial black-holes (PBH) can be produced in single-field models of inflation with a quasi-inflection point in the potential. In these models, a large production of PBHs requires a deviation from the slow-roll (SR) trajectory. In turn, this SR violation can produce an exponential growth of quantum fluctuations. We study the back-reaction of these quantum modes on the inflationary dynamics using stochastic inflation in the Hamilton-Jacobi formalism. We develop a methodology to solve quantum diffusion beyond SR in terms of the statistical moments of the probability distribution. We apply these techniques to a toy model potential with a quasi-inflection point. We find that there is an enhancement of the power spectrum due to the dominance of the stochastic noise in the phase beyond SR. Moreover, non-Gaussian corrections become as well relevant with a large positive kurtosis. Altogether, this produces a significant boost of PBH production. We discuss how our results extend to other single-field models with similar dynamics. We conclude that the abundance of PBHs in this class of models should be revisited including quantum diffusion.Comment: 17+7 pages, 5 figures. Matches JCAP versio

Towards the most general scalar-tensor theories of gravity: a unified approach in the language of differential forms

We use a description based on differential forms to systematically explore the space of scalar-tensor theories of gravity. Within this formalism, we propose a basis for the scalar sector at the lowest order in derivatives of the field and in any number of dimensions. This minimal basis is used to construct a finite and closed set of Lagrangians describing general scalar-tensor theories invariant under Local Lorentz Transformations in a pseudo-Riemannian manifold, which contains ten physically distinct elements in four spacetime dimensions. Subsequently, we compute their corresponding equations of motion and find which combinations are at most second order in derivatives in four as well as arbitrary number of dimensions. By studying the possible exact forms (total derivatives) and algebraic relations between the basis components, we discover that there are only four Lagrangian combinations producing second order equations, which can be associated with Horndeski's theory. In this process, we identify a new second order Lagrangian, named kinetic Gauss-Bonnet, that was not previously considered in the literature. However, we show that its dynamics is already contained in Horndeski's theory. Finally, we provide a full classification of the relations between different second order theories. This allows us to clarify, for instance, the connection between different covariantizations of Galileons theory. In conclusion, our formulation affords great computational simplicity with a systematic structure. As a first step we focus on theories with second order equations of motion. However, this new formalism aims to facilitate advances towards unveiling the most general scalar-tensor theories.Comment: 28 pages, 1 figure, version published in PRD (minor changes

Fuentes para el estudio de la narrativa breve en lengua inglesa

En el presente ensayo bibliográfico he intentado reunir las ediciones más significativas de narrativa breve en lengua inglesa de los siglos XVI y XVII, incluyendo entre las mismas algunas traducciones al inglés de obras en lenguas románicas. La lista de obras primarias va precedida de una valoración crítica de los principales argumentos esgrimidos por los historiadores de la novela para justificar los dos auges o "rises" de la novela inglesa: el florecimiento de la ficción humanista en las postrimerías del reinado de Isabel Tudor, en el cual se produjo la aparición de obras como Euphues de John Lyly, The Unfortunate Traveller de Thomas Nashe y Jack of Newbury de Thomas Deloney; y el surgimiento de la novela burguesa, localizado por la mayoría de estudiosos, a partir de Ian Watt, en 1719, cuando Daniel Defoe publica su popular Robinson Crusoe._____________________________________In this bibliographical essay I have endeavored to take account of the most significant modern editions of sixteenth- and seventeenthcentury short fiction in English (including some translations from romance languages), itemizing the contents of the multiple-author anthologies and single-author collections. The list of primary works is preceded by a critical assessment of a number of important arguments on the two "rises" of the English novel: the flourishing of humanist fiction in the later years of Elizabeth Tudor's rule, which saw the appearance of such short works as John Lyly's Euphues, Thomas Nashe's The Unfortunate Traveller, and Thomas Deloney's Jack of Newbury; and the emergence of the bourgeois novel, which most literary historians, following Ian Watt's lead, situate in 1719, with the publication of Daniel Defoe's immensely popular Robinson Crusoe

New lab-on-a-chip strategies for enantio-selective and non-diffusion-limited biosensing

The race for fast and small that drives nowadays society has also reached the field of biosensing. Looking for efficient and cost effective biosensors for applications including screening and treatment monitoring, biomolecular engineering, drug design and food industry; plasmonics and microfluidics technologies have synergistically grown to offer the most attractive solutions. The recent progress in nano-optics has paved the route toward the development of highly sensitive and label-free optical transducers using the localized surface plasmon resonance (LSPR). Additionally, LSPR offer high-end miniaturization and high degree of tunability of both sensors’ spatial and spectral responses. These unique properties have recently been interfaced with microfluidics towards lab-on-a-chip (LOC) functional platforms which offer reduced sample volumes and multi-tasking operations on a single chip. Combining nano-optics, microfluidics and biochemical sensing makes this PhD project highly multidisciplinary. This blend aims at pushing the limits of LSPR sensing by addressing two significant problems in the biosensing community. On one hand, we went through chiral plasmonic sensing. Chiral molecules exhibit signatures in the ultraviolet frequency region. They are typically characterized by circular dichroism (CD), which suffers of low sensitivity and the need of big sample volumes and concentrations. Plasmonic nanostructures have the potential to enhance the sensitivity of chiral detection and translate the molecular signatures to the visible spectral range. However, to date, it remains unclear which properties plasmonic sensors should exhibit to maximize this effect and apply it to reliable enantiomer discrimination. As a consequence, a collection of results of difficult interpretation and cross comparison can be found in the literature. Here, we bring further insight into this complex problem and present a chiral plasmonic sensor composed of a racemic mixture of gammadions that enables us to directly differentiate enantiomers. We also present a plasmo-fluidic sensing platform, which allows the systematic study of chiral biomolecules by enabling multiple sensing assays on a single chip. On the other hand, we addressed one of the major challenges of plasmonic sensing in microfluidics environments; the transport of the analyte to the sensor surface, which due to the laminar flow that rules in micro-channels, is limited by Brownian diffusion. Hence, dictates the total duration of the sensing assay. Here, we use the electrothermoplasmonic (ETP) effect to overcome this limit through opto-electrical fluid convective flow generation. To this end, we designed a LSPR sensing chip that integrates ETP operation into state-of-the-art microfluidics. Our results demonstrate that ETP-LSPR has improved performances over standard LSPR.La continua carrera de la miniaturización y la velocidad, que gobierna la sociedad tecnológica de hoy en día, ha alcanzado también el campo de los bio-sensores. Plasmónica y micro-fluídica, dos tecnologías complementarías, han crecido durante sinérgicamente en las últimas. Juntas son capaces de atender la exigente demanda de soluciones más efectivas y económicas en campos como el diagnóstico y tratamiento médico personalizado, la ingeniería bio-molecular, el diseño de fármacos y la industria alimentaria. El reciente progreso del campo de la nano-óptica ha forjado el camino para el desarrollo de sensores ópticos altamente sensibles y sin requerimiento de marcadores moleculares. Los sensores basados en resonancias plasmónicas superficiales localizadas (LSPR) son de gran atractivo debido a sus posibilidades de miniaturización y versatilidad en la caracterización de sus respuestas espaciales y espectrales. Estas propiedades únicas se han combinado recientemente con la micro-fluídica, dando lugar a plataformas funcionales integradas, conocidas como laboratorios en un chip (LOC). Dichas plataformas permiten reducir significativamente los volúmenes de muestra, además de realizar multiples operaciones en un solo chip. La combinación de la nano-óptica, la microfluídica y la detección bioquímica hacen de este proyecto de doctorado una tarea altamente multidisciplinar. Esta mezcla opta por llevar los límites de los sensores LSPR enfrentando dos de los problemas más notables en las últimas décadas: la detección de moléculas quirales mediante plasmónica y transporte molecular en micro-canales. Las moléculas quirales muestran respuestas ópticas en el rango ultravioleta del espectro y son comúnmente caracterizadas mediante dicroísmo circular (CD). Sin embargo, dicha respuesta óptica es minúscula y requieres grandes concentraciones y volúmenes de muestra para ser media. La plasmónica tiene el potencial de aumentar sensibilidad de los métodos actuales y además trasladar la respuesta quiral al rango visible. Aunque hasta la fecha, no se han conseguido predecir las propiedades óptimas que deben poseer los sensores para realizar dicha tarea de forma eficiente. En consecuencia, existen una variedad de trabajos publicados difíciles de interpretar y de enlazar. En este sentido hemos conseguido desarrollar un sensor compuesto por una mezcla racémica de cruces gamadas que es capaz de diferenciar entre enantiómeros de forma directa. Además, también presentamos una plataforma plasmónica y fluídica que permite el estudio sistemático de moléculas quirales mediante la realización de multiples ensayos simultáneos en un solo chip. Por otro lado, abordamos la limitación del transporte de moléculas por difusión browniana en micro-canales. Un problema que limita la velocidad en la detección de los sistemas que integran sensores plasmónicos con la microfluídica. En este frente, utilizamos el efecto electro-termo-plasmónico (ETP) para rebasar este límite a través de la generación de flujos convectivos que alteran el flujo laminar que impera en los micro-canales. Con este fin, hemos diseñado un chip que integra el estado del arte de la microfluídica con el efecto ETP. Los resultados que ofrecemos demuestran que el rendimiento de un ensayo en el nuevo sistema ETP-LSPR es superior al realizado en un LSPR estándar.Postprint (published version

Alta fidelidad. El uso inmaduro de las imágenes digitales en la arquitectura

[EN] As regards architectural digital design, computer rendered images seem to be the least accomplished and most controversial feature whereas other graphic tools have successfully developed in the realms of architectural creation and production.The wish for authenticity associated with this kind of rendering can trigger a number of malfunctions The search for role models, the fast obsolescence prompted by the consumer’s increasingly trained perception, the loss aversion factor, the unrealistic innovation expectations, and the exclusivity originated by technical complexity, in the pursuit of achieving status or concealing faulty approaches, can be counted among the factors that can help us to understand and foresee the limitations in front of us.[ES] Las imágenes generadas por ordenador (render), parecen ser el aspecto peor logrado, menos acertado y más controvertido del dibujo arquitectónico digital, mientras que otras herramientas gráficas digitales han conseguido un desarrollo satisfactorio y específico en la producción e ideación arquitectónicas. La pretensión de verosimilitud (realismo) de este tipo de visualización puede ser el desencadenante de otras muchas disfunciones. La búsqueda de referentes propios, su carácter meramente comercial como producto final, la rápida obsolescencia producida por la percepción cada vez más educada del receptor, el factor nostálgico de pérdida, el falso aporte producido por unas desvanecidas expectativas de originalidad e innovación, la exclusividad generada por las complejidades técnicas utilizadas para obtener un estatus o enmascarar planteamientos débiles, son algunos de los factores que nos pueden ayudar a comprender y pronosticar las limitaciones con que nos encontramos.García Crespo, JM. (2021). High fidelity. The immature use of digital images for architecture. EGA Expresión Gráfica Arquitectónica. 26(42):156-167. https://doi.org/10.4995/ega.2021.14628OJS156167264

A "quick look" at ultrafast ablation using fs-resolved phase-change microscopy

A pump-probe phase-change microscope with fs temporal resolution has been used to understand the transformation induced in the sample surface as a consequence of laser-matter interaction.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Alcohol decomposition on basic/acid lignin-derived submicron diameter carbon fibers

The use of lignin, the second most abundant polymer in nature, along with a simple and versatile technique, electrospinning, represents an advantageous and promising approach for the preparation of carbon fibers. In previous studies, we have demonstrated that the incorporation of H3PO4 to the initial lignin solution allows for shortening the carbon fibers preparation process and that the resulting carbon fibers present P-surface groups that are of great interest for heterogeneous catalysis. Different carbon fibers catalysts have been prepared by electropinning of Alcell lignin in the absence or presence of H3PO4 as chemical activating agent. Carbonization at different temperatures between 500 and 1600 ºC allows for preparing carbon fibers with a high variety of porosity and chemical surface properties. Diverse oxygen surface groups are presented on the carbon catalysts surface. The isopropanol decomposition has been used as a catalytic test to study the acid or basic character of the prepared carbon fibers. Carbon fibers without phosphorus surface groups generate acetone as the main product of the isopropanol decomposition reaction, from 400 to 600 ºC, suggesting the basic character of these catalysts. On the contrary, phosphorus-containing carbon fibers show high acid character, producing selectivity to propylene of 100 % at temperatures between 250 and 350 ºC. The most acid carbon fiber catalyst produced a high selectivity to ethylene and dimethyl ether for the decomposition of ethanol and methanol, respectively. The conversion enhancement that the presence of oxygen in the gas phase produced for all these reactions was also studied.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech. MINECO (CTQ2015-68654-R). MINECO (PTA2015-11464-I)