77823 research outputs found
Sort by
Squaring the circle of the circular economy. The need to properly account for scarcity to guide mineral resource management
Get PDFOver the last decades, extractivism and its derived socio-ecological impacts have increased exponentially, suggesting that prices of minerals are poor indicators of their absolute scarcity. Aware that we need to move towards a more circular economy (CE), we propose a methodology which builds on the use of an exergy-based indicator of absolute scarcity to create the much-needed taxonomy of mineral substances to make CE-oriented policies more effective. This indicator will not only allow overcoming the limitations usually attributed to physical indicators as scarcity's proxy measures. Transcending the usual mass-based approach to absolute scarcity, it warns that depletion is more about the loss of mineral quality than quantity, which is fundamental in a physical world governed by the Law of Entropy where ore grades decline over time. Even more, beyond enabling the calibration of economic tools to ensure we move towards circularity, this indicator can also set the basis for designing depletion charges targeted at raising social awareness and putting upward pressure on prices well before reserves are exhausted. Our methodology will also allow providing new insights into mineral price formation. By warning that we must learn from the biosphere, we argue that society can reach sustainability if it increases the use of renewable resources while moving towards that of abundant, recyclable, and physically easy-to-obtain mineral substances. In so doing, not only we show the importance of interdisciplinary work. We also point to the relevance of integrating weak and strong sustainability approaches in economics, thus avoiding the existing divorce between monetary and physical analyses
Electrostatic technology for pesticide application. Prototype characterization and validation in super-intensive olive crops
Get PDFElectrostatic technology for agricultural crops has been studied in recent decades to improve pesticide deposition by applying voltage to droplets, which maximizes the amount of product reaching the deepest areas of the canopy through attractive forces. However, few studies perform a comprehensive laboratory characterization of a sprayer followed by field validation in order to explore the possibility of reduced amount of chemicals, specifically for super-intensive olive cultivation.
This study aimed to conduct a laboratory evaluation of an electrostatic sprayer prototype designed for three-dimensional hedge crops and validate its performance through field experiments. Sprayer configurations associated with activated or deactivated electrostatic system (ES vs. NES, respectively) were tested. The characterization included airflow evaluation, product distribution profile, charge-to-mass ratio (CMR) quantification, and deposition trials, varying application parameters such as liquid pressure, airflow setup, and distance under controlled environmental conditions. A differentiation between adaxial and abaxial areas of the artificial target during deposition assays was also carried out. Finally, field trials compared the electrostatic sprayer to conventional application methods, providing practical insights into pesticide reduction efficiency. Laboratory results showed no differences in flow rate (L min−1) between ES and NES configurations at any tested pressure. The total accumulated volume from the vertical distribution profile showed variations associated with airflow configuration and liquid pressure as a function of distance. Deposition results revealed higher coverage and deposition when the electrostatic system was activated, regardless of distance or height, with a 70 % increase in abaxial areas compared to the NES. Field trials in super-intensive olive orchards revealed good performance in terms of coverage and deposition on artificial receptors and leaves after application with the electrostatic equipment, particularly at the highest application dose (163.3 L ha−1) compared to the conventional spraying (466.3 L ha−1), highlighting a 60 % reduction in application volume. Additionally, ground losses were significantly lower with the electrostatic sprayer, as coverage and deposition at the base of the trunk were substantially reduced compared to conventional equipment
Exploring the role of halogen bond donors in the thiourea‐catalyzed Friedel–Crafts alkylation reaction
No full textHalogen bonding (XB) has recently emerged as a powerful tool in organocatalysis, though asymmetric applications remain scarce. Here we report the first synergistic system combining a chiral thiourea and an inert XB donor. The iodine derivative enhances substrate activation via LP(I)→π*(C = C) interactions. Instead, a strong π–π interaction between the catalysts rules out direct thiourea activation. Applied to asymmetric Friedel–Crafts alkylation, iodoethynyl cocatalysts boost both reactivity and enantioselectivity. DFT calculations rationalize the crucial role of the XB donor, highlighting a new strategy to exploit non‐covalent interactions in asymmetric synthesis
Exploring the interaction of alkali metal cations with the tetramethylborate anion
Get PDFUnderstanding the interactions between metallic cations and anions is crucial for elucidating the structure and reactivity of ionic systems. In this work, we investigate the binding modes and energetic characteristics of a series of alkali metal cations (Li+, Na+, K+, Rb+, Cs+) with the tetramethylborate anion using density functional theory. Molecular electrostatic potential analysis reveals three preferential binding regions corresponding to distinct local minima on the tetramethylborate surface. Geometry optimizations and penetration index analysis confirm the formation of ion pairs with site-specific interaction modes: κ¹C, κ²C, and κ¹B. Energy decomposition analysis shows that electrostatics dominates the interaction energy, with polarisation playing a significant secondary role. Correlations between penetration indices and interaction energies provide insight into the nature of cation–anion interactions, including the role of collective stabilisation effects. These findings contribute to a deeper understanding of ion pairing phenomena in organoborate-based systems and the broader field of supramolecular chemistry
Las guías RECIDA de recursos de información: herramientas para promover la lectura y la educación ambiental
Get PDFLas guías de recursos elaboradas por la Red de Centros de Información y Documentación Ambiental (RECIDA) se constituyen como producto documental de alta calidad con utilidad para la animación a la lectura y para la educación y sensibilización ambiental. El estudio examina 18 guías publicadas entre 2014 y 2025 a través de una metodología basada en el análisis documental y apoyada en el análisis de contenido estructural y la estadística descriptiva, con el fin de caracterizar las guías elaboradas por la red en términos de contenido, autoría, colaboración e impacto. Los resultados muestran un aumento significativo en la producción de guías a partir de 2021, aunque con una marcada asimetría temporal. Se constata una alta participación de los centros de la red RECIDA y una mayoría femenina en las autorías y responsabilidades. Se identifican 4 grandes tipologías: guías técnico-académicas, educativas, literarias o mixtas, con una amplia variedad de recursos y enfoques temáticos (generales o especializados). Asimismo, la mayoría de las guías se especializan en temáticas relacionadas con el patrimonio natural, o con la interacción entre las personas y su entorno. Las guías se muestran como herramientas relevantes para facilitar el acceso a información confiable y relevante en el ámbito ambiental, de utilidad para profesionales de diversos ámbitos
High Pressure-Based Synthesis of Nanoporous Metal–Organic Framework ZIF-93 Giving Rise to a Phase for Proton Conduction
Get PDFThis study aims to develop a green, solvent-free synthesis of ZIF-93 (ZIF stands for zeolitic imidazolate framework) and to explore the formation of different phases. We report the solvent-free synthesis of a previously unreported nanoporous ZIF phase, ZIF-93_HP (HP referring to “high-pressure”), from zinc oxide using a dual high-pressure (150 MPa) and thermal (110 °C) method. The influence of key synthesis parameters, such as the amount of NH4NO3 promotor and reaction steps, was systematically investigated to maximize the conversion of ZnO into the intermediate ZIF-93_HP, while, in parallel, preventing its further conversion into nanoporous ZIF-93 phase. The material was extensively characterized by X-ray diffraction, thermogravimetry, electron microscopy and N2 and CO2 adsorption, which revealed insights into the structure, morphology and nanoporosity of ZIF-93_HP. ZIF-93_HP, with empirical formula of Zn(C5N2OH5)2·1.2(NH4NO3)·(H2O), is related to the previously reported ZIF-93 (Zn(C5N2OH5)2). Water washing of this phase led to the transformation into ZIF-93 and a significant increase in the BET specific surface area (from 4 to 181 m2/g). In addition, the presence of NH4+ and NO3– ions into its structure makes ZIF-93_HP proton conductor at room temperature and moisture conditions (3.76 × 10–3 S/cm), a property that decreases with increasing temperature due to dehydration. The discovery of ZIF-93_HP highlights the potential of the high-pressure, solvent-free synthesis as a powerful tool for the exploration of different ZIFs and reticular materials that are inaccessible through traditional solvothermal methods. As crystallization under solvent-free conditions is often influenced by nonthermodynamic equilibrium, this approach holds a great potential for expanding the material landscape by enabling the discovery of different phases and structures with unique properties, such as the promising proton conductivity demonstrated here
Constelaciones de la casi-nada
Get PDFConstelaciones de la casi-nada Las antiguas civilizaciones comenzaron a agrupar estrellas uniéndolas con trazos invisibles. Imaginaban figuras que podían contener astros cercanos o muy distantes, pero cuya posición estable servía como guía en la navegación. Hoy, quien observa la esfera celeste, puede ver millones de puntos luminosos o puede distinguir Andrómeda o Casiopea. La lectura de estas agrupaciones imaginarias no dependerá del ojo que mira, sino de la memoria entrenada y dispuesta a interpretar esas conexiones que distan, en el mejor de los casos, unos pocos años luz.La arquitectura contemporánea bebe y se enriquece de un sinfín de fuentes. Un conjunto de textos, melodías e imágenes reside en nuestro imaginario y cobra sentido gracias a los hilos invisibles que les confieren una forma inteligible. Este trabajo trata de recoger la naturaleza de los trazos que sostienen indeformable la constelación de la casi-nada, que proponemos como guía al habitar de un tiempo por venir.Con la inestabilidad que al comienzo de la IIGM arrastra al viejo continente al desánimo, da comienzo un viaje. Los avances de la ciencia, un nuevo paradigma y la corriente de pensamiento pragmatista llevará a los protagonistas de esta investigación a descubrir al otro lado del océano el abundante material con el que se dibuja lo próximo: la nada. Diferentes autores, artistas o arquitectos, despojados de todo lo prescindible, de lo superfluo y banal, anhelarán manipular esa nada ontológica y hacerla visible, investigando la manera de atrapar el umbral -de belleza sublime- entre el ser y la nada. La búsqueda de lo nuevo invita a estos viajeros a romper con lo conocido para hallar, en la ausencia, la promesa lo nuevo.Aquellos creadores que tras el encuentro con la nada deciden acomodarse en ella comienzan a trabajar en sus improvisados laboratorios domésticos recorriendo un camino al margen que discurre al borde del vacío, entre la existencia y el abismo del no ser. Ahí, en sus estudios y talleres comienzan a arrojar los astros que recogemos en esta constelación.Los protagonistas que hemos seleccionado, los viajeros que en su travesía hacia lo nuevo -hacia la nada- dan con la bella aparición de la casi-nada, son capaces de advertir la caducidad de todo lo conocido y se instalan a caballo entre dos realidades, la conocida y la próxima. Ellos no son ya actores de la contemporaneidad, son autores de un tiempo nuevo.Soñando el nuevo habitar nuestros viajeros se preguntan: ¿No será momento de pensar una morada consciente de la finitud de este tiempo? ¿No merece aquel que también quiere ser viajero una habitación sin artificios que permita gozar del encuentro con el horizonte de la nada? El ser contemporáneo transcendente, aquel que anhela liberarse de las distracciones y el ruido que aleja de lo sustancial será quien quizá quiera guiarse por este mapa que hemos dibujado.Proponemos, de entre todas las posibles, una constelación que pueda resultar útil en el ejercicio arquitectónico a quien ambicione enfrentarse desde el ser, al horizonte del no ser, de la nada, de lo eterno.La vida es una actividad que se ejecuta hacia adelante ¿escribe Ortega y Gasset-. La vida es fruición, es lo que aún no es. Desde el témenos que ya descubrieron los viajeros autores de nuestra constelación soñaremos no solo mirar, sino como ellos hicieran, proponer eso que aún no es, proponer la habitación de un tiempo próximo.<br /
Chiral optics in corrugated metasurfaces interacting with atomic-width semiconductors
Get PDFLa óptica quiral es una subárea de la óptica que estudia la interacción de la luz con materiales quirales. En esta tesis, nos centramos en una estructura prometedora: metasuperficies corrugadas interactuando con semiconductores de anchura atómica, analizando teóricamente sus propiedades ópticas quirales.En este trabajo, revisamos el marco teórico mínimo necesario para estudiar metasuperficies plasmónicas compuestas por matrices de agujeros rectangulares en láminas metálicas. Utilizando el método de modos acoplados, desarrollamos un nuevo formalismo que permite obtener directamente los coeficientes de reflexión en el campo lejano. Los acoplamientos geométricos son los elementosclave de este procedimiento, ya que establecen las conexiones entre los distintos órdenes de Bragg en el espacio de polarización.Derivamos las ecuaciones que rigen las metasuperficies e identificamos tanto los términos responsables del spin-momentum locking, que establecen reglas de selección entre la polarización y el momento de los órdenes de difracción, como los términos que rompen este comportamiento al mezclar componentes de espín. Esta ruptura se atribuye a la discrepancia entre la definición de luz circularmente polarizada, relativa a la dirección de propagación de los órdenes de difracción correspondientes, y las simetrías del sistema, definidas con respecto a la dirección z de la metasuperficie.Demostramos que, aunque esta ruptura puede ser despreciable en algunos casos, particularmente cuando los vectores de onda en el plano son pequeños, se vuelve fundamental cuando se excitan plasmones de superficie. En este último caso, pueden establecerse unas reglas de selección modificadas para el spin-momentum locking, interpretándose como un proceso de dispersión en dos pasos que involucra la excitación y desexcitación secuencial de un plasmón.Estos resultados se obtienen también a partir de un formalismo complementario basado en la resolución de las amplitudes del campo eléctrico en las aperturas, en lugar de mediante el nuevo enfoque que involucra directamente los coeficientes de reflexión. Este procedimiento alternativo nos permite encontrar expresiones analíticas para las amplitudes del campo cercano y esclarecer el papel de las resonancias plasmónicas en las propiedades quirales de las superficies corrugadas.Asimismo, exploramos la interacción entre metasuperficies quirales y materiales bidimensionales, observando dicroísmo circular en las monocapas debido a la quiralidad inducida por la metasuperficie. Cuando el material 2D se coloca sobre un separador dieléctrico, demostramos que pueden excitarse resonantemente modos de guía de onda de polarización transversal-eléctrica inducidos por el separador, los cuales también producen dicroísmo circular en el material 2D. Este sistema obedece otro conjunto de reglas de selección modificadas para el spin-momentum locking, en las cuales el carácter transversal-eléctrico de estos modos sustituye al carácter transversal-magnético de los plasmones.Aplicamos el formalismo desarrollado para (i) estudiar una capa idealizada de moléculas quirales y (ii) analizar separadamente la absorción en los valles K/K0 de una monocapa de WS2. Además, extendemos nuestro análisis a nanoestructuras más sofisticadas, en particular, cavidades quirales, derivando las ecuaciones del sistema compuesto por una matriz de agujeros sobre a una matriz de hendiduras.Finalmente, exploramos el concepto de topología en sistemas fuertemente acoplados. Proponemos un modelo mínimo que presenta la ruptura de la correspondencia borde-volumen observada en estudios previos de sistemas complejos, cuyo origen aún no se ha explicado completamente. Nuestro modelo mínimo consiste en una cadena de primeros vecinos en un modelo tight-binding acoplada a una cadena Su-Schrieffer-Heeger. Nuestro trabajo descarta algunos mecanismos posibles de esta ruptura y presenta nueva fenomenología asociada a la ruptura de la correspondencia borde-volumen.Chiral optics is a subfield of optics that explores the interaction of light with chiral materials. In this thesis, we focus on a promising structure: corrugated metasurfaces interacting with atomic-width semiconductors, and study theoretically its chiral optical properties. In this work, we review the minimal theoretical framework to study plasmonic metasurfaces comprised of arrays of rectangular holes in metallic slabs. Using the coupled-mode method, we develop a novel formalism that directly obtains the reflection coefficients for the far-field. The geometric couplings are the key ingredients of this new approach because they establish the connections between different Bragg orders in polarisation space. We derive the governing equations of the bare metasurfaces and identify both the terms responsible for the spin-momentum locking, which establish selection rules between the polarisation and the momentum of the diffraction orders, and the terms that spoil this behaviour by mixing the spin components. These breakdown terms are ascribed to the mismatch between the definition of circularly polarised light, relative to the propagation direction of the corresponding diffraction orders, and the system symmetries, defined with respect to the -direction of the metasurface. We demonstrate that even though this breakdown can be neglected in some cases, particularly for small in-plane wavevectors, it becomes critical when surface plasmon polaritons are excited. In the latter case, a modified set of spin-momentum locking selection rules can be established, being interpreted as a two-step scattering process involving the sequential excitation and de-excitation of a plasmon. We also derive these results from a complementary formalism based on solving the amplitudes of the electric field at the apertures rather than from the novel approach involving the reflection coefficients directly. This alternate procedure allows us to find analytical expressions for the near-field amplitudes and elucidate the role of plasmonic resonances in the chiral properties of corrugated surfaces. We explore the interaction between chiral metasurfaces and two-dimensional materials, observing circular dichroism in the monolayers due to the chirality induced by the metasurface. When the 2D material is placed on top of a dielectric spacer, we demonstrate that transverse-electric spacer-induced waveguide modes can be resonantly excited, also inducing circular dichroism in the 2D material. This system satisfies another set of modified spin-momentum locking selection rules, including the transverse-electric character of these modes instead of the transverse-magnetic character of the plasmons. We apply the developed formalism to (i) study an idealised layer of chiral molecules and (ii) perform separate absorption analyses in both / valleys of a WS monolayer. We extend our analysis to more sophisticated nanostructures, namely chiral cavities, deriving the equations of the system composed of a hole array placed over a dimple array. Finally, we explore the concept of topology in strongly coupled systems. We propose a minimal model that presents the bulk-edge correspondence breakdown observed in previous works in complex systems, which is still unexplained. Our minimal model consists of a first-nearest-neighbours tight-binding chain coupled to a Su-Schrieffer-Heeger chain. Our work rules out some possible mechanisms for the breakdown and presents new bulk-edge correspondence breakdown phenomenology.<br /
Connecting the dots: from SDGs to well-being
Get PDFPurpose – Sustainable Development Goals (SDGs) are gaining traction globally, yet limited empirical evidence exists on how national characteristics influence SDGs achievement and how this success translates into citizens’ well-being. The paper develops and tests a model examining the influence of governance, political and economic factors on SDG achievement and the subsequent relationship between SDG accomplishments and perceived well-being.
Design/methodology/approach – Using data from the United Nations (UN) database on SDGs, the World Happiness Index, democracy metrics and Gross Domestic Product (GDP) statistics, the study analyses 96 countries in 2022. Partial Least Squares Structural Equation Modelling (PLS-SEM) is employed to uncover
intricate relationships and dependencies among variables.
Findings – The results indicate that strong coordination for meeting SDGs, i.e. SDG17, high democracy levels and country wealth significantly enhance SDG achievements. In turn, successful SDG implementation positively influences citizen well-being, suggesting that sustainability efforts have meaningful everyday effects.
Practical implications – Governance emerges as another key enabler for SDG achievement alongside political and economic factors. The findings highlight the importance of investments in governance capacity and the recognition of SDG targets as reflections of deeper socioeconomic mechanisms and well-being drivers and not just as standalone goals. Furthermore, our findings pose challenges in public financial management on a dual front. Firstly, whether more accounting-based ratios can better track SDG achievement and improve transparency and comparability. Secondly, whether a new system of accounting based on well-being indicators should be developed to illuminate the sustainability-well-being nexus and inform sociopolitical and environmental decision-making.
Originality/value – The study underscores governance as a central aspect to SDG successful achievement and citizen well-being, affirming the role of public administration in enhancing happiness