1,032 research outputs found

    Closed-loop Control from Data-Driven Open-Loop Optimal Control Trajectories

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    We show how the recent works on data driven open-loop minimum-energy control for linear systems can be exploited to obtain closed-loop piecewise-affine control laws, by employing a state-space partitioning technique which is at the basis of the static relatively optimal control. In addition, we propose a way for employing portions of the experimental input and state trajectories to recover information about the natural movement of the state and dealing with non-zero initial conditions. The same idea can be used for formulating several open-loop control problems entirely based on data, possibly including input and state constraints

    Time-Dependent Analysis of Precast Segmental Bridges

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    Prestressed segmentally constructed balanced cantilever bridges are often subjected to larger deflections than those predicted by calculations, especially for long-term effects. In this paper, the case of modular balanced cantilever bridges, which are prestressed segmental bridges obtained through a repetition of the same double cantilever, is investigated. The considered bridges are two typical cases of modular balanced cantilever both subjected to large deformations during their lifetime. In this case, due to the unusual employed static scheme, creep deflections indefinitely evolve over time particularly at the end of the cantilevers and in correspondence with the central joint. These remarkable deflections cause discomfort for vehicular traffic and in certain cases can lead to the bridge collapse. Important extraordinary maintenance interventions were necessary to restore the viability of the bridges and to replace the viaduct design configuration. To this aim, the static schemes of the structures were varied, introducing new constraints, new tendons, and carbon fiber reinforcements. In the present work, time analysis was performed to compare the time-dependent behavior of the bridge according to two different creep models, the CEB-FIP Model Code 2010 and the RILEM Model B3, with the real-time-dependent behavior of the bridge observed during its lifetime. The two different employed models exhibit different behaviors in terms of displacements and bending moments acting on the bridge. Interesting considerations are made on their reliability in simulating the long-term creep effects that evolve indefinitely over time. Moreover, retrofitting techniques have been proposed and modeled to predict their effectiveness in reducing time-dependent deflections

    The vascular flora of the Marine Protected Area of "Capo Carbonara" (SE-Sardinia)

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    This study aims at presenting an updated inventory of the vascular flora of the Capo Carbonara Marine Protected Area, including the Sites of Community Importance “Isola dei Cavoli, Serpentara, Punta Molentis e Campulongu” and partially of “Costa di Cagliari”, in Sardinia (Italy). A total of 653 taxa are reported, 84% of which are native (5% endemics) and 16% non-native (10% neophytes, 6% archaeophytes). The native component includes 406 species, 135 subspecies, two variety and one hybrid, belonging to 75 families and 313 genera. The non-native taxa are 94 species, 13 subspecies, one variety and one hybrid, belonging to 40 families and 81 genera. Life-form analysis of native species revealed a prevalence of therophytes (49%) followed by hemicryptophytes (21%), geophytes (14%) and chamaephytes (7%). Therophytes (33%) fol lowed by phanerophytes (32%) are prevalent among the non-native taxa. Biogeographically, among native species, the Mediterranean element is largely prevailing (81%), mainly consisting of Circum-Mediterranean (39%) and Euro-Mediterranean (27%) taxa, while the American ele ment (35%) prevails over the Mediterranean species (29%) among the non-native taxa. Among endemics, the Sardo-Corsican taxa are dominant (55%), followed by Sardo-Corsican-Tuscan Archipelago (14%) and Sardinian (10%) taxa

    Experimental study on the in-plane response of adobe masonry wallets strengthened with textile reinforced matrix systems

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    Seismic strengthening of existing adobe masonry (AM) buildings has been recognized as a critical issue due to the dramatic consequences of recent seismic events occurred especially in developing countries, where a great part of the population lives in those constructions. Previous studies investigated the effectiveness of different retrofitting techniques by means of experimental programs consisting of either dynamic or static tests on reduced- or full-scale specimens, representing partial or complete AM dwellings. In this study, the output of diagonal compression tests on adobe masonry panels before and after external strengthening are presented. Three series of specimens were tested, namely, unreinforced and strengthened wallets with textile reinforced matrix (TRM) systems made of either hemp or glass meshes. Those tests benefitted from the characterization of the mud mortar that was used for both masonry joints and matrix, representing typical characteristics of existing Italian AM buildings. Main testing outcomes obtained for the AM wallets, particularly in terms of observed damage and response curves, are presented and discussed. In the end, the effectiveness of the applied TRM systems in the improvement of shear strength and ductility capacity is assessed

    Experimental in-plane lateral response of a full-scale adobe masonry wall with opening

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    A large amount of world population lives nowadays in earthen buildings, often constructed only based on construction practice and within earthquake-prone regions. In the recent history, several strong earthquakes had dramatic consequences on these structures, highlighting their significant seismic vulnerability due to multiple reasons, such as poor mechanical properties, poor detailing, and large inertia mass. Several aspects of seismic performance of existing earthen constructions need to be investigated through full-scale experimental testing. In this regard, the present study aims at contributing to the investigation by testing a full-scale adobe masonry wall with a central door-type opening under in-plane lateral loading with cyclic fashion. The mechanical behaviour of materials, specimen's design, loading protocol and instrumentation setup are described. The experimental response curves, observed damage evolution and failure mode are discussed, especially focusing on dissipation capacity of the wall

    Comprehensive Assessment of Robustness in Fairness of GNN-based Recommender Systems against Attacks

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    The robustness of recommendation models is typically measured by their ability to maintain the original utility when exposed to attacks. In contrast, robustness in fairness pertains to the resilience of fairness levels in the presence of such attacks. Despite its significance, this latter area remains largely underexplored. In this extended abstract, we evaluate the robustness of graph-based recommender systems with respect to fairness from both the consumer and provider perspectives, under attacks involving edge-level perturbations. We analyze the impact of these perturbations on fairness through an experimental protocol involving three datasets and three graph neural networks. Our findings reveal severe fairness issues, particularly on the consumer side, where fairness is compromised to a greater extent than on the provider side. Source code: https://github.com/jackmedda/CPFairRobust

    A Structured and Unstructured grid Relocatable ocean platform for Forecasting (SURF)

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    We present a numerical platform named Structured and Unstructured grid Relocatable ocean platform for Forecasting (SURF). The platform is developed for short-time forecasts and is designed to be embedded in any region of the large-scale Mediterranean Forecasting System (MFS) via downscaling. We employ CTD data collected during a campaign around the Elba island to calibrate and validate SURF. The model requires an initial spin up period of a few days in order to adapt the initial interpolated fields and the subsequent solutions to the higher-resolution nested grids adopted by SURF. Through a comparison with the CTD data, we quantify the improvement obtained by SURF model compared to the coarse-resolution MFS model

    Model-free cable robot control

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    This paper proposes a technique to control a cable robot in the total absence of a model and its parameters. The cable robot is actuated by three motors whose data, including exact positions, pulley diameters, and nominal cable length, are unknown. We just assume to have a very rough knowledge of lower and upper bounds for the partial derivatives of the relation between the cable lengths and the end-effector space coordinates. A structured-light sensor measures the end-effector position, and the goal is to drive it to a designated point. An algorithm is proposed with guaranteed convergence based on the so-called model-free plant tuning approach. No learning stage is required. Experimental results are reported

    Global and Regional IUCN Red List Assessments: 17

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    In this contribution, the conservation status assessment of three vascular plants according to IUCN categories and criteria are presented. It includes the assessment of Campanula bergomensis F.Mangili & L.Mangili, Iris hippolyti (Vved.) Kamelin and Stipa aktauensis Roshev. at global level
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