833 research outputs found

    Evaluating Architectural Safeguards for Uncertain AI Black-Box Components

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    Although tremendous progress has been made in Artificial Intelligence (AI), it entails new challenges. The growing complexity of learning tasks requires more complex AI components, which increasingly exhibit unreliable behaviour. In this book, we present a model-driven approach to model architectural safeguards for AI components and analyse their effect on the overall system reliability

    Automatic and Accurate Performance Prediction in Distributed Systems

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    System performance is getting attention by industry as it affects user experience, and much research focused on performance evaluation approaches. Profiling is the most straightforward approach to performance evaluation of software systems, despite being limited to shallow analyses. Conversely, software performance models excel in representing complex interactions between components. Still, practitioners do not integrate performance models in the software development cycle, as the learning curve is too steep, and the approaches do not adapt well to incremental development practices. In this thesis, we propose three approaches towards automatic learning of performance models. The first approach employs a Recurrent Neural Network (RNN) to extract a full Queueing Network (QN) model of the system; the second one calibrates a Layered Queueing Network (LQN) using an RNN; the third one presents μP, a framework that allows the user to develop microservice systems and obtain the corresponding LQN model from source code analysis. We considered the microservices architecture as it is embraced by influential players (e.g., Amazon, Netflix). Those approaches have two advantages: i) minimal user intervention to flatten the learning curve; ii) continuous synchronization between software and performance model, such as each software development iteration is reflected on the model. We validated our approaches on several benchmarks taken from the literature. The models we generate can be queried to predict the system behavior under conditions significantly different from the learning setting, and the results show sensible advancements in the quality of the predictions

    Measuring the impact of COVID-19 on hospital care pathways

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    Care pathways in hospitals around the world reported significant disruption during the recent COVID-19 pandemic but measuring the actual impact is more problematic. Process mining can be useful for hospital management to measure the conformance of real-life care to what might be considered normal operations. In this study, we aim to demonstrate that process mining can be used to investigate process changes associated with complex disruptive events. We studied perturbations to accident and emergency (A &E) and maternity pathways in a UK public hospital during the COVID-19 pandemic. Co-incidentally the hospital had implemented a Command Centre approach for patient-flow management affording an opportunity to study both the planned improvement and the disruption due to the pandemic. Our study proposes and demonstrates a method for measuring and investigating the impact of such planned and unplanned disruptions affecting hospital care pathways. We found that during the pandemic, both A &E and maternity pathways had measurable reductions in the mean length of stay and a measurable drop in the percentage of pathways conforming to normative models. There were no distinctive patterns of monthly mean values of length of stay nor conformance throughout the phases of the installation of the hospital’s new Command Centre approach. Due to a deficit in the available A &E data, the findings for A &E pathways could not be interpreted

    Intégration des méthodes formelles dans le développement des RCSFs

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    In this thesis, we have relied on formal techniques in order to first evaluate WSN protocols and then to propose solutions that meet the requirements of these networks. The thesis contributes to the modelling, analysis, design and evaluation of WSN protocols. In this context, the thesis begins with a survey on WSN and formal verification techniques. Focusing on the MAC layer, the thesis reviews proposed MAC protocols for WSN as well as their design challenges. The dissertation then proceeds to outline the contributions of this work. As a first proposal, we develop a stochastic generic model of the 802.11 MAC protocol for an arbitrary network topology and then perform probabilistic evaluation of the protocol using statistical model checking. Considering an alternative power source to operate WSN, energy harvesting, we move to the second proposal where a protocol designed for EH-WSN is modelled and various performance parameters are evaluated. Finally, the thesis explores mobility in WSN and proposes a new MAC protocol, named "Mobility and Energy Harvesting aware Medium Access Control (MEH-MAC)" protocol for dynamic sensor networks powered by ambient energy. The protocol is modelled and verified under several features

    LIPIcs, Volume 261, ICALP 2023, Complete Volume

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    LIPIcs, Volume 261, ICALP 2023, Complete Volum

    Tools to study cytoadhesion of P. falciparum-infected erythrocytes under flow

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    Plasmodium falciparum infected erythrocytes are able to bind to a multitude of extracellular receptors through adhesins expressed on their membrane. The molecular interactions involved in parasite binding to these receptors are only partly understood, although the trait itself is well-known and used as an early indicator of severe malaria diagnosis and progress of infection. Binding to the microvasculature of blood vessels or the intervillous spaces of the placenta, ensures the survival of the parasite as it avoids splenic clearance in the later stages of maturation. In this thesis, the importance of sheer flow and cell morphology in binding dynamics of parasitized erythrocytes is further highlighted. While static adhesion assays would showcase similar amounts of cells adhering in different maturation stages, when observed in flow, this picture changes drastically. Trophozoite stage parasites seem to bind less frequently but more efficiently onto the simulated endothelium. In the last stage of maturation, schizont stage parasites alter the cell morphology to such an extent that adhesion is more likely but with less contact area and density of involved receptors. Changes in the membrane morphology between AA and AS erythrocytes also underline the significance of receptor presentation and accessibility influencing binding efficiency. The effects of a P. falciparum infection during primigravida are threatening to both the mother and the foetus, as infected erythrocytes sequester to the maternal side of the syncytiotrophoblast that lines the placenta. Despite the tremendous efforts in the field, the adhesive tropism of infected erythrocytes that leads to placental sequestration remains unsolved. In this thesis, I determined that measurements are not possible without the full length protein and interactions between the receptor and its erythrocyte-expressed ligand are not specific enough to distinguish from negative control experiments. Another form of cell adhesion investigated in this thesis is the formation of so-called rosettes, that form when an infected erythrocyte binds to non-infected erythrocytes. Rosette formation is considered either an indication of severe malaria or a symptom of progressed infection and is believed to propagate the severity of infection by obstructing smaller vasculature and normal blood flow. in this thesis, I developed a platform to study the position of rosettes within a channel in flow, in order to determine their margination tendance. In those experiments, I verified that regardless of haematocrit value and size of rosette, rosettes remain in flow and do not marginate towards the walls of the flow chamber

    Migratory behaviour and year-round distribution of two goose species

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    Knowledge on flyway structures, year-round spatiotemporal distributions and migration strategies is a key for understanding the ecology of migratory populations and the evolution of migratory behaviours. Knowledge on these factors is also a prerequisite to reliably estimate the size and trend of migratory populations, and to successfully conserve and manage them. In this thesis, I studied the migratory behaviour of two goose species, the bean goose (Anser fabalis) and the greylag goose (Anser anser) using high-resolution satellite tracking, traditional neckbanding and birdwatcher observations. Satellite tracked taiga bean geese belonging to the Central Flyway population revealed a comprehensive moult migration of non-breeding and unsuccessfully breeding birds to the Arctic. This behaviour increases the length of the annual migration distance and delays the autumn migration of moult migrants. The strength of migratory connectivity among the population was moderate to low between breeding and nonbreeding areas, and both migratory connectivity and the spatial distribution of the population varied substantially within the non-breeding season. Additionally, satellite tracking indicated that the current population censuses might underestimate the size of the taiga bean goose population. Birdwatcher observations showed both spatial and temporal difference in occurrence of different bean goose subspecies in Finland during spring and autumn migrations, which affects the harvest management of the subspecies with different conservation statuses. The satellite tracking data and neckband resightings of greylag geese confirmed the existence of a gradual migratory divide in the continuous breeding distribution of the species. The birds breeding at the different ends of the greylag goose breeding distribution in Finland used different flyways (Western and Central), and the birds breeding between these two extremes scattered to the two flyways. The migration strategies differed between the flyways. The overall migratory journey is longer for birds using the Western Flyway, and these birds migrate earlier in autumn and later in spring than birds on the Central Flyway. Birds using the Western Flyway also show a clear stopover of around one month during their autumn migration, whereas Central Flyway birds migrate relatively straight from their breeding grounds to their wintering sites. The results of the thesis help to delineate the flyways of both species, provide aspects needed to understand their ecology, and supports the ongoing international management of the species. Furthermore, the results build possibilities to further study not only these two species, but also more general ecological questions related to bird migration and movement ecology.Kahden hanhilajin muuttokäyttäytyminen ja vuodenkierron aikainen esiintyminen Populaatiotason muuttoreittien, muuttostrategioiden ja koko vuodenkierron aikaisten esiintymisalueiden tunteminen on edellytys muuttavien eläinten ekologian ja muuttokäyttäytymisen evoluution ymmärtämiseksi. Se on myös ennakkoedellytys muuttavien eläinten kannan koon ja kehityksen arvioinnille sekä menestyksekkäälle kannanhoidolle ja suojelulle. Tutkin väitöskirjassani kahden hanhilajin, metsähanhen (Anser fabalis) ja merihanhen (Anser anser) muuttokäyttäytymistä käyttäen korkean resoluution satelliittiseurantaa, perinteisiä lukurenkaita ja lintuharrastajien havaintoaineistoa. Satelliittiseuranta paljasti keskiseen osapopulaatioon kuuluvien, pesimättömien ja pesinnässään epäonnistuneiden taigametsähanhien muuttavan kesäisin säännönmukaisesti Arktikselle sulkasatoa varten. Sulkasatomuutto tundralle yli kaksinkertaistaa näiden lintujen vuotuisen muuttomatkan ja viivästyttää niiden syysmuuttoa populaation muihin yksilöihin verrattuna. Taigametsähanhipopulaation kytkeytyneisyys pesimäalueiden ja lintujen muina vuodenaikoina käyttämien alueiden välillä on kohtalaista tai heikkoa, ja populaation kytkeytyneisyys sekä sen esiintymisalueen laajuus vaihtelevat voimakkaasti vuodenkierron aikana. Satelliittiseurannan perusteella nykyiset laskennat aliarvioivan taigametsähanhien määrän. Lintuharrastajien havaintoaineisto osoittaa metsähanhien eri alalajien esiintymisen eroavan toisistaan sekä ajallisesti että maantieteellisesti syys- ja kevätmuuton aikaan Suomessa, mikä on vaikuttaa lajin optimaaliseen metsästyksen säätelyyn. Merihanhien satelliittiseuranta ja kaularengashavainnot vahvistivat, että lajin levinneisyysalueella Suomessa on niin sanottu vaiheittainen muutonjakaja. Levinneisyysalueen ääripäissä linnut käyttävät eri muuttoreittejä (keskistä ja läntistä reittiä), ja levinneisyysalueen keskiosista linnut hajaantuvat näille kahdelle reitille. Myös merihanhien muuttostrategia eroaa muuttoreittien välillä. Läntistä reittiä käyttävien lintujen vuotuinen muuttomatka on pidempi, ja linnut muuttavat aiemmin syksyllä ja myöhemmin keväällä kuin keskistä muuttoreittiä käyttävät linnut. Läntistä muuttoreittiä käyttävät linnut pysähtyvät levähtämään noin kuukaudeksi kesken syysmuuton, kun taas keskistä muuttoreittiä käyttävät linnut muuttavat pesimäalueiltaan pysähdyksittä talvehtimisalueilleen. Väitöskirjani tulokset auttavat molempien lajien populaatiotason muuttoreittien hahmottamisessa, niiden ekologian ymmärtämisessä ja tukevat lajien kansainvälistä kannanhoitoa. Lisäksi tulokset luovat edellytyksiä tutkia jatkossa yleisiä ekologisia kysymyksiä lintujen muuttoon ja liikkumisekologiaan liittyen

    Brain Computations and Connectivity [2nd edition]

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    This is an open access title available under the terms of a CC BY-NC-ND 4.0 International licence. It is free to read on the Oxford Academic platform and offered as a free PDF download from OUP and selected open access locations. Brain Computations and Connectivity is about how the brain works. In order to understand this, it is essential to know what is computed by different brain systems; and how the computations are performed. The aim of this book is to elucidate what is computed in different brain systems; and to describe current biologically plausible computational approaches and models of how each of these brain systems computes. Understanding the brain in this way has enormous potential for understanding ourselves better in health and in disease. Potential applications of this understanding are to the treatment of the brain in disease; and to artificial intelligence which will benefit from knowledge of how the brain performs many of its extraordinarily impressive functions. This book is pioneering in taking this approach to brain function: to consider what is computed by many of our brain systems; and how it is computed, and updates by much new evidence including the connectivity of the human brain the earlier book: Rolls (2021) Brain Computations: What and How, Oxford University Press. Brain Computations and Connectivity will be of interest to all scientists interested in brain function and how the brain works, whether they are from neuroscience, or from medical sciences including neurology and psychiatry, or from the area of computational science including machine learning and artificial intelligence, or from areas such as theoretical physics
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