1,921 research outputs found

    Exploring transition metal catalysis in water for <i>in vivo </i>applications

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    Transition metal catalysis proves a powerful tool to achieve otherwise synthetically challenging, or even impossible, transformations with (high) selectivity and is therefore employed in various areas of chemistry. Recently, transition metal-catalysed reactions have been successfully performed in cells (in vitro) and living systems (in vivo). The achievements made thus far reveal the potential of transition metal catalysis and its applications in such biological settings. Interestingly, the scope is limited compared to the breadth of transition metal-catalysed reactions that have been unlocked for synthetic applications. Translating transition metal-catalysed reactions from flasks to cells is non-trivial as the conditions in cells are fairly different compared to the highly controlled and adaptable conditions achieved in a flask. The development of catalytic systems for future applications in vivo therefore proceeds through many steps, starting with evaluating their reactivity, selectivity, and stability in water and under biologically relevant and biomimetic conditions. By exploring transition metal-catalysed reactions in water for in vivo applications, this dissertation has contributed to the subfield of bioorthogonal chemistry devoted to complementing Nature’s repertoire of reactions. Our studies have revealed the challenges associated with the performance of transition metal catalysis in aqueous media and how a detailed understanding of a catalytic system can address them. Apart from these fundamental studies, we have performed explorative studies under biologically relevant and biomimetic conditions in the context of intracellular drug synthesis. Moreover, we have developed a new and compatible protocol that enables detailed kinetic studies in complex reaction media, comparable to the cellular environment, to facilitate the translation of transition metal catalysis from flasks to cells

    Multidisciplinary perspectives on Artificial Intelligence and the law

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    This open access book presents an interdisciplinary, multi-authored, edited collection of chapters on Artificial Intelligence (‘AI’) and the Law. AI technology has come to play a central role in the modern data economy. Through a combination of increased computing power, the growing availability of data and the advancement of algorithms, AI has now become an umbrella term for some of the most transformational technological breakthroughs of this age. The importance of AI stems from both the opportunities that it offers and the challenges that it entails. While AI applications hold the promise of economic growth and efficiency gains, they also create significant risks and uncertainty. The potential and perils of AI have thus come to dominate modern discussions of technology and ethics – and although AI was initially allowed to largely develop without guidelines or rules, few would deny that the law is set to play a fundamental role in shaping the future of AI. As the debate over AI is far from over, the need for rigorous analysis has never been greater. This book thus brings together contributors from different fields and backgrounds to explore how the law might provide answers to some of the most pressing questions raised by AI. An outcome of the Católica Research Centre for the Future of Law and its interdisciplinary working group on Law and Artificial Intelligence, it includes contributions by leading scholars in the fields of technology, ethics and the law.info:eu-repo/semantics/publishedVersio

    AI: Limits and Prospects of Artificial Intelligence

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    The emergence of artificial intelligence has triggered enthusiasm and promise of boundless opportunities as much as uncertainty about its limits. The contributions to this volume explore the limits of AI, describe the necessary conditions for its functionality, reveal its attendant technical and social problems, and present some existing and potential solutions. At the same time, the contributors highlight the societal and attending economic hopes and fears, utopias and dystopias that are associated with the current and future development of artificial intelligence

    Accurate quantum transport modelling and epitaxial structure design of high-speed and high-power In0.53Ga0.47As/AlAs double-barrier resonant tunnelling diodes for 300-GHz oscillator sources

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    Terahertz (THz) wave technology is envisioned as an appealing and conceivable solution in the context of several potential high-impact applications, including sixth generation (6G) and beyond consumer-oriented ultra-broadband multi-gigabit wireless data-links, as well as highresolution imaging, radar, and spectroscopy apparatuses employable in biomedicine, industrial processes, security/defence, and material science. Despite the technological challenges posed by the THz gap, recent scientific advancements suggest the practical viability of THz systems. However, the development of transmitters (Tx) and receivers (Rx) based on compact semiconductor devices operating at THz frequencies is urgently demanded to meet the performance requirements calling from emerging THz applications. Although several are the promising candidates, including high-speed III-V transistors and photo-diodes, resonant tunnelling diode (RTD) technology offers a compact and high performance option in many practical scenarios. However, the main weakness of the technology is currently represented by the low output power capability of RTD THz Tx, which is mainly caused by the underdeveloped and non-optimal device, as well as circuit, design implementation approaches. Indeed, indium phosphide (InP) RTD devices can nowadays deliver only up to around 1 mW of radio-frequency (RF) power at around 300 GHz. In the context of THz wireless data-links, this severely impacts the Tx performance, limiting communication distance and data transfer capabilities which, at the current time, are of the order of few tens of gigabit per second below around 1 m. However, recent research studies suggest that several milliwatt of output power are required to achieve bit-rate capabilities of several tens of gigabits per second and beyond, and to reach several metres of communication distance in common operating conditions. Currently, the shortterm target is set to 5−10 mW of output power at around 300 GHz carrier waves, which would allow bit-rates in excess of 100 Gb/s, as well as wireless communications well above 5 m distance, in first-stage short-range scenarios. In order to reach it, maximisation of the RTD highfrequency RF power capability is of utmost importance. Despite that, reliable epitaxial structure design approaches, as well as accurate physical-based numerical simulation tools, aimed at RF power maximisation in the 300 GHz-band are lacking at the current time. This work aims at proposing practical solutions to address the aforementioned issues. First, a physical-based simulation methodology was developed to accurately and reliably simulate the static current-voltage (IV ) characteristic of indium gallium arsenide/aluminium arsenide (In-GaAs/AlAs) double-barrier RTD devices. The approach relies on the non-equilibrium Green’s function (NEGF) formalism implemented in Silvaco Atlas technology computer-aided design (TCAD) simulation package, requires low computational budget, and allows to correctly model In0.53Ga0.47As/AlAs RTD devices, which are pseudomorphically-grown on lattice-matched to InP substrates, and are commonly employed in oscillators working at around 300 GHz. By selecting the appropriate physical models, and by retrieving the correct materials parameters, together with a suitable discretisation of the associated heterostructure spatial domain through finite-elements, it is shown, by comparing simulation data with experimental results, that the developed numerical approach can reliably compute several quantities of interest that characterise the DC IV curve negative differential resistance (NDR) region, including peak current, peak voltage, and voltage swing, all of which are key parameters in RTD oscillator design. The demonstrated simulation approach was then used to study the impact of epitaxial structure design parameters, including those characterising the double-barrier quantum well, as well as emitter and collector regions, on the electrical properties of the RTD device. In particular, a comprehensive simulation analysis was conducted, and the retrieved output trends discussed based on the heterostructure band diagram, transmission coefficient energy spectrum, charge distribution, and DC current-density voltage (JV) curve. General design guidelines aimed at enhancing the RTD device maximum RF power gain capability are then deduced and discussed. To validate the proposed epitaxial design approach, an In0.53Ga0.47As/AlAs double-barrier RTD epitaxial structure providing several milliwatt of RF power was designed by employing the developed simulation methodology, and experimentally-investigated through the microfabrication of RTD devices and subsequent high-frequency characterisation up to 110 GHz. The analysis, which included fabrication optimisation, reveals an expected RF power performance of up to around 5 mW and 10 mW at 300 GHz for 25 μm2 and 49 μm2-large RTD devices, respectively, which is up to five times higher compared to the current state-of-the-art. Finally, in order to prove the practical employability of the proposed RTDs in oscillator circuits realised employing low-cost photo-lithography, both coplanar waveguide and microstrip inductive stubs are designed through a full three-dimensional electromagnetic simulation analysis. In summary, this work makes and important contribution to the rapidly evolving field of THz RTD technology, and demonstrates the practical feasibility of 300-GHz high-power RTD devices realisation, which will underpin the future development of Tx systems capable of the power levels required in the forthcoming THz applications

    Towards a better characterization of submicron aerosol in the Mediterranean basin

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    Programa de Doctorat en Física / Tesi realitzada a l'Institut de Diagnòstic Ambiental i Estudis de l'Aigua (IDAEA - CSIC)[eng] Atmospheric aerosol is an ensemble of atmospheric pollutants with a severe impact on human health and Earth climate. Particulate Matter (PM) effects vary depending on the composition and size. However, current air quality guidelines (AQG) from WHO and from the EU Commission only define threshold standards for bulk PM10 and PM2.5 concentrations. In terms of health, the smaller the particles, the deeper they penetrate into the respiratory system, and they can even diffuse into the bloodstream and circulate to other parts of the organism. The adverse effects on the tissues in which they are deposited depend on the PM composition. Regarding climate, PM size and composition relevantly affect many aerosol-radiation direct and indirect interactions, which regulate troposphere temperature. Consequently, the consideration of these properties is relevant for present and future climate descriptions. Barcelona, the city where this study focuses, is located in the Mediterranean basin, a region with high complexity in terms of air pollution, hence, the nature of this enclave requires thorough monitoring of PM in order to protect the population from exposition accurately. This dissertation focuses on submicronic aerosol evolution over the last decade, with a more detailed study for May 2014-May 2015 and September 2017-October 2018. The objective of this thesis is to describe the PM1 sources in Barcelona by means of source apportionment (SA) techniques. The Positive Matrix Factorisation (PMF) algorithm is one of the most widely used approaches for SA and is the tool used in this dissertation. A secondary aim of this study is the improvement of the SA methodology itself. This is accomplished by testing the outcomes of new methodologies involving the more automatic analysis and dataset junction with several approaches. A field-deployed aerosol mass spectrometer was used at the Barcelona site for continuous PM1 measurements, and SA was performed on Organic Aerosol (OA). First, SA was tackled from a conventional methodology, the seasonal PMF, then, the novel rolling PMF methodology was tested and compared to the fore one. Finally, a comprehensive PM1 SA was performed based on an ensemble of different datasets coming from a variety of measurement techniques. These steps enabled a progressive aerosol composition understanding and acknowledgement of subsequent aerosol trends. A PM1 concentrations decrease was found in the 2014-2018 period, a trend confirmed by other studies at the site. Its relative composition changed significantly; a decrease was found for SO42-, BC, and NH4+, while NO3- increased and OA levels were found stable. The OA SA revealed that its sources were: secondary OA (SOA, >55-70%), road traffic OA (12-19%), cooking-like OA (14-18%), and biomass burning OA (4-6%). These sources are similar to those reported in other sites across the Mediterranean region. In this study, all the primary OA sources were found in a clear decrease from 2014 to 2018. An increasing SOA proportion and SOA oxidation state were also observed. These increments could be explained by a likely increase in the oxidation capacity of the atmosphere, related to the accumulation of oxidative radicals reported in many cities. In order to bridge the possible inter-annual variability in that period, the time period was elongated (2014-2021) detecting the same underlying trends. With the aim of further climate and health impact aerosol impact assessment, this thesis provides mid-term PM1 sources diagnosis. SOA is especially concerning in terms of health effects, hence this pollutant is to be continuously monitored to deeply understand its precursors and formation mechanisms to design effective abatement policies.[cat] L’aerosol atmosfèric és un conjunt de contaminants atmosfèrics amb un impacte sever sobre la salut humana i el clima. Els efectes del material particulat (PM) varien depenent de la seva composició i mida. Barcelona, la ciutat en què es centra aquest estudi, està localitzada a la conca mediterrània, una regió d’alta complexitat en termes de contaminació de l’aire. Per tant, requereix un monitoratge conscienciós del PM per tal de protegir la població acuradament de la seva exposició. Aquesta tesi es focalitza en l’evolució del PM submicrònic (PM1) al llarg de l’última dècada, amb un estudi més detallat per als períodes maig 2014 - maig 2015 i setembre 2017 - octubre 2018. L'objectiu d'aquesta tesi és descriure les fonts de PM1 a Barcelona per mitjà de tècniques de contribució de fonts (SA). L'algoritme de Factorització de Matriu Positiva (PMF) és un dels enfocaments més utilitzats per al SA o és l'eina emprada per a aquesta dissertació. Un objectiu secundari d'aquesta tesi és la millora de la pròpia metodologia del SA. Això és executat per mitjà del testatge a través de diferents metodologies. Les mesures de PM1 es van dur a terme a través d’un espectròmetre de masses instal·lat a l'estació de Barcelona. El SA va ser executat per a l'Aerosol Orgànic (OA) submicrònic mesurat a partir d’aquest instrument, aplicant diferents metodologies per a avaluar-ne l’exactitud. Finalment, un estudi detallat del SA de PM1 va ser executat basat en un conjunt de dades provinents de diferents tècniques de mesura. Aquests passos van permetre la comprensió progressiva de la composició i el reconeixement de les tendències subjacents de l'aerosol. Un dels resultats més rellevants consisteix en la detecció d'una tendència creixent del SOA independentment de la disminució del PM1, relacionat amb el decreixement de l'OA primari. A més, pel que fa al SA, aquesta tesi proposa diverses modificacions del protocol. El SOA és especialment preocupant pels seus efectes en la salut, per tant, aquest contaminant ha de ser contínuament monitorejat amb tècniques de SA per tal d'entendre els seus precursors i mecanismes de formació amb l'objectiu de dissenyar mesures de mitigació efectives

    Optimisation for Optical Data Centre Switching and Networking with Artificial Intelligence

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    Cloud and cluster computing platforms have become standard across almost every domain of business, and their scale quickly approaches O(106)\mathbf{O}(10^6) servers in a single warehouse. However, the tier-based opto-electronically packet switched network infrastructure that is standard across these systems gives way to several scalability bottlenecks including resource fragmentation and high energy requirements. Experimental results show that optical circuit switched networks pose a promising alternative that could avoid these. However, optimality challenges are encountered at realistic commercial scales. Where exhaustive optimisation techniques are not applicable for problems at the scale of Cloud-scale computer networks, and expert-designed heuristics are performance-limited and typically biased in their design, artificial intelligence can discover more scalable and better performing optimisation strategies. This thesis demonstrates these benefits through experimental and theoretical work spanning all of component, system and commercial optimisation problems which stand in the way of practical Cloud-scale computer network systems. Firstly, optical components are optimised to gate in 500ps\approx 500 ps and are demonstrated in a proof-of-concept switching architecture for optical data centres with better wavelength and component scalability than previous demonstrations. Secondly, network-aware resource allocation schemes for optically composable data centres are learnt end-to-end with deep reinforcement learning and graph neural networks, where 3×3\times less networking resources are required to achieve the same resource efficiency compared to conventional methods. Finally, a deep reinforcement learning based method for optimising PID-control parameters is presented which generates tailored parameters for unseen devices in O(103)s\mathbf{O}(10^{-3}) s. This method is demonstrated on a market leading optical switching product based on piezoelectric actuation, where switching speed is improved >20%>20\% with no compromise to optical loss and the manufacturing yield of actuators is improved. This method was licensed to and integrated within the manufacturing pipeline of this company. As such, crucial public and private infrastructure utilising these products will benefit from this work

    Soundscape in Urban Forests

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    This Special Issue of Forests explores the role of soundscapes in urban forested areas. It is comprised of 11 papers involving soundscape studies conducted in urban forests from Asia and Africa. This collection contains six research fields: (1) the ecological patterns and processes of forest soundscapes; (2) the boundary effects and perceptual topology; (3) natural soundscapes and human health; (4) the experience of multi-sensory interactions; (5) environmental behavior and cognitive disposition; and (6) soundscape resource management in forests

    Data ethics : building trust : how digital technologies can serve humanity

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    Data is the magic word of the 21st century. As oil in the 20th century and electricity in the 19th century: For citizens, data means support in daily life in almost all activities, from watch to laptop, from kitchen to car, from mobile phone to politics. For business and politics, data means power, dominance, winning the race. Data can be used for good and bad, for services and hacking, for medicine and arms race. How can we build trust in this complex and ambiguous data world? How can digital technologies serve humanity? The 45 articles in this book represent a broad range of ethical reflections and recommendations in eight sections: a) Values, Trust and Law, b) AI, Robots and Humans, c) Health and Neuroscience, d) Religions for Digital Justice, e) Farming, Business, Finance, f) Security, War, Peace, g) Data Governance, Geopolitics, h) Media, Education, Communication. The authors and institutions come from all continents. The book serves as reading material for teachers, students, policy makers, politicians, business, hospitals, NGOs and religious organisations alike. It is an invitation for dialogue, debate and building trust! The book is a continuation of the volume “Cyber Ethics 4.0” published in 2018 by the same editors
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