131 research outputs found

    Mechanisms of natural and forced variability in the southern ocean

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    The Southern Ocean is an important regulator of global climate, and accurately predicting its future evolution under climate change constitutes a critical scientific challenge. Mesoscale eddies are key to the dynamics of the Southern Ocean, but the mechanisms and time scales of their natural and forced variability are not completely understood. Motivated by the dynamical analogy between the Antarctic Circumpolar Current and the tropospheric jet stream, the natural variability of eddymean flow interaction is studied by adapting a two-dimensional model of storm track variability to the oceanic case. It is found that eddies and the mean flow interact according to a predator-prey oscillatory relationship in both an idealised, eddy-resolving, channel configuration and the SOSE state estimate product of the Southern Ocean. The oscillatory nature of the dynamics reflects in the structure of the phase space diagrams, where quasi-periodic cycles with typical timescales of a few weeks can be observed. The simplified mathematical model qualitatively captures the statistical properties of the interaction well. The time scales of forced adjustment are investigated by means of an ensemble of wind step-change experiments run with the idealised channel configuration. It is found that the temperature response is driven largely, but not exclusively, by changes in the ocean’s circulation, with enhanced mixing also playing an important role. Circulation changes have a rich spatial structure, and vertical/meridional displacements of the residual overturning circulation cells have a large impact on the temperature response even though the channel is strongly eddy-compensated. The time scales of the response vary across the domain, and are set by the spin-up of baroclinic eddies. The results presented in this Thesis bring the fundamental mechanisms of eddy variability into clearer focus, and inform the interpretation of more realistic numerical simulations of the Southern Ocean

    Automatic extraction of robotic surgery actions from text and kinematic data

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    The latest generation of robotic systems is becoming increasingly autonomous due to technological advancements and artificial intelligence. The medical field, particularly surgery, is also interested in these technologies because automation would benefit surgeons and patients. While the research community is active in this direction, commercial surgical robots do not currently operate autonomously due to the risks involved in dealing with human patients: it is still considered safer to rely on human surgeons' intelligence for decision-making issues. This means that robots must possess human-like intelligence, including various reasoning capabilities and extensive knowledge, to become more autonomous and credible. As demonstrated by current research in the field, indeed, one of the most critical aspects in developing autonomous systems is the acquisition and management of knowledge. In particular, a surgical robot must base its actions on solid procedural surgical knowledge to operate autonomously, safely, and expertly. This thesis investigates different possibilities for automatically extracting and managing knowledge from text and kinematic data. In the first part, we investigated the possibility of extracting procedural surgical knowledge from real intervention descriptions available in textbooks and academic papers on the robotic-surgical domains, by exploiting Transformer-based pre-trained language models. In particular, we released SurgicBERTa, a RoBERTa-based pre-trained language model for surgical literature understanding. It has been used to detect procedural sentences in books and extract procedural elements from them. Then, with some use cases, we explored the possibilities of translating written instructions into logical rules usable for robotic planning. Since not all the knowledge required for automatizing a procedure is written in texts, we introduce the concept of surgical commonsense, showing how it relates to different autonomy levels. In the second part of the thesis, we analyzed surgical procedures from a lower granularity level, showing how each surgical gesture is associated with a given combination of kinematic data

    International Conference on Mathematical Analysis and Applications in Science and Engineering – Book of Extended Abstracts

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    The present volume on Mathematical Analysis and Applications in Science and Engineering - Book of Extended Abstracts of the ICMASC’2022 collects the extended abstracts of the talks presented at the International Conference on Mathematical Analysis and Applications in Science and Engineering – ICMA2SC'22 that took place at the beautiful city of Porto, Portugal, in June 27th-June 29th 2022 (3 days). Its aim was to bring together researchers in every discipline of applied mathematics, science, engineering, industry, and technology, to discuss the development of new mathematical models, theories, and applications that contribute to the advancement of scientific knowledge and practice. Authors proposed research in topics including partial and ordinary differential equations, integer and fractional order equations, linear algebra, numerical analysis, operations research, discrete mathematics, optimization, control, probability, computational mathematics, amongst others. The conference was designed to maximize the involvement of all participants and will present the state-of- the-art research and the latest achievements.info:eu-repo/semantics/publishedVersio

    Technology Integration Leaders: A Leaders’ Community of Practice to Negotiate Meaning, Craft a Vision, and Establish Value

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    Because leaders influence teachers’ pedagogical development, a team of administrative and technological leaders participated in a community of practice (CoP) at an international school in the Netherlands. The purpose was to align thinking, craft a shared technology integration (TI) vision, and develop expectations for teachers to integrate technology into their pedagogy. Although the needs assessment started before the pandemic, the timing coincided with COVID-19 and the world’s emergency reaction to teaching online. The needs assessment in 2018 was measured using the Levels of Technology Innovation Digital Age Survey for Leaders and an adapted version of Principals and Teachers Perceptions of Technology Integration. The results revealed that 37 school leaders valued TI for its potential to enhance instruction. However, the school did not share a common understanding, vision, or expectation of TI across the elementary, middle, and high schools. An intervention program for administrative and technology leaders was initiated in April of 2021. Using a leader’s CoP framework, 11 participants experienced professional learning to negotiate and craft a shared TI vision. Seven of the 11 leaders participated in seven or more sessions. Participants benefited from leveraging pedagogical and technology expertise to shape understanding, craft the shared vision, and develop expectations for the CoP to continue with teacher members. During and after the CoP, leaders began applying the knowledge and initiatives, reflecting the shared vision throughout the school

    Agroforestry-Based Ecosystem Services

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    As a dynamic interface between agriculture and forestry, agroforestry has only recently been formally recognized as a relevant part of land use with ‘trees outside forest’ in important parts of the world—but not everywhere yet. The Sustainable Development Goals have called attention to the need for the multifunctionality of landscapes that simultaneously contribute to multiple goals. In the UN decade of landscape restoration, as well as in response to the climate change urgency and biodiversity extinction crisis, an increase in global tree cover is widely seen as desirable, but its management by farmers or forest managers remains contested. Agroforestry research relates tree–soil–crop–livestock interactions at the plot level with landscape-level analysis of social-ecological systems and efforts to transcend the historical dichotomy between forest and agriculture as separate policy domains. An ‘ecosystem services’ perspective quantifies land productivity, flows of water, net greenhouse gas emissions, and biodiversity conservation, and combines an ‘actor’ perspective (farmer, landscape manager) with that of ‘downstream’ stakeholders (in the same watershed, ecologically conscious consumers elsewhere, global citizens) and higher-level regulators designing land-use policies and spatial zoning

    Gamma-ray Bursts: 15 Years of GRB Afterglows

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    Gamma-ray bursts (GRB) are amongst the most energetic phenomena in the Universe. In 1997 (more than 15 years ago), BeppoSAX allowed the detection of the first GRB X-ray afterglow, leading to the detection of afterglows at other wavelengths (optical, radio) in the following years, probing the cosmological distance scale. There are still many other open issues which still need to be addressed, regarding both theoretical and observational aspects: prompt emission and afterglow physics, progenitors (including Pop III stars), host galaxies, multi-messenger information, etc

    Coupled climate response to Atlantic Multidecadal Variability in a multi-model multi-resolution ensemble

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    North Atlantic sea surface temperatures (SSTs) underwent pronounced multidecadal variability during the 20th and early 21st century. We examine the impacts of this Atlantic Multidecadal Variability (AMV), also referred to as the Atlantic Multidecadal Oscillation (AMO), on climate in an ensemble of five coupled climate models at both low and high spatial resolution. We use a SST nudging scheme specified by the Coupled Model Intercomparision Project's Decadal Climate Prediction Project Component C (CMIP6 DCPP-C) to impose a persistent positive/negative phase of the AMV in the North Atlantic in coupled model simulations; SSTs are free to evolve outside this region. The large-scale seasonal mean response to the positive AMV involves widespread warming over Eurasia and the Americas, with a pattern of cooling over the Pacific Ocean similar to the Pacific Decadal Oscillation (PDO), together with a northward displacement of the inter-tropical convergence zone (ITCZ). The accompanying changes in global atmospheric circulation lead to widespread changes in precipitation. We use Analysis of Variance (ANOVA) to demonstrate that this large-scale climate response is accompanied by significant differences between models in how they respond to the common AMV forcing, particularly in the tropics. These differences may arise from variations in North Atlantic air-sea heat fluxes between models despite a common North Atlantic SST forcing pattern. We cannot detect a widespread effect of increased model horizontal resolution in this climate response, with the exception of the ITCZ, which shifts further northwards in the positive phase of the AMV in the higher resolution configurations

    Classification and detection of Critical Transitions: from theory to data

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    From population collapses to cell-fate decision, critical phenomena are abundant in complex real-world systems. Among modelling theories to address them, the critical transitions framework gained traction for its purpose of determining classes of critical mechanisms and identifying generic indicators to detect and alert them (“early warning signals”). This thesis contributes to such research field by elucidating its relevance within the systems biology landscape, by providing a systematic classification of leading mechanisms for critical transitions, and by assessing the theoretical and empirical performance of early warning signals. The thesis thus bridges general results concerning the critical transitions field – possibly applicable to multidisciplinary contexts – and specific applications in biology and epidemiology, towards the development of sound risk monitoring system

    A detailed study of the barium central star of the planetary nebula Abell 70

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    We present a detailed study of the barium star at the heart of the planetary nebula Abell 70. Time-series photometry obtained over a period of more than 10 yr demonstrates that the barium-contaminated companion is a rapid rotator with temporal variability due to spots. The amplitude and phasing of the photometric variability change abruptly; however, there is no evidence for a change in the rotation period (P = 2.06 d) over the course of the observations. The co-addition of 17 high-resolution spectra obtained with Ultraviolet and Visual Échelle Spectrograph mounted on the Very Large Telescope allows us to measure the physical and chemical properties of the companion, confirming it to be a chromospherically active, late G-type sub-giant with more than +1 dex of barium enhancement. We find no evidence of radial velocity variability in the spectra, obtained over the course of approximately 130 d with a single additional point some 8 yr later, with the radial velocities of all epochs approximately −10 km s −1 from the previously measured systemic velocity of the nebula. This is perhaps indicative that the binary has a relatively long period (P ≳ 2 yr) and high eccentricity (e ≳ 0.3), and that all the observations were taken around radial velocity minimum. However, unless the binary orbital plane is not aligned with the waist of the nebula or the systemic velocity of the binary is not equal to the literature value for the nebula, this would imply an unfeasibly large mass for the nebular progenitor
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