1,721,404 research outputs found
Detection of Influential Nodes in Network Dynamical Systems from Time Series
No full textIdentifying influential nodes in network dynamical systems requires the manipulation of topological and dynamic characteristics within ideal experiments. However, seldom we have access to experimental settings that could afford targeted interventions or to calibrated mathematical models that could support faithful what/if analyses. Our knowledge of the network dynamical system is often limited to the time series of individual nodes in some real experiments. Using these time series, it is possible to undertake a number of inference tasks, from reconstructing the topology of the network to discovering hidden nodes. Whether time series of real experiments could help pinpoint causal influence within the network is an open question. Here, we address this question in the context of synchronization problems, where the influence of a node is defined as the extent to which adding noise at that particular node affects the overall synchronization of the entire network. For linear time-invariant dynamics and undirected topologies, we demonstrate the possibility of exactly detecting the most influential nodes in the network without a calibrated mathematical model, using only time series of a real experiment, where all nodes are plagued by noise. Beyond illustrating our results on classical and second-order consensus protocols, we consider two real-world datasets: 1) 1) firearm prevalence in the USA and 2) players' movements in a soccer game. Just as our conclusions support the emergence of influential states, which have a less stringent legal environment, they hint at the instrumental role of players, who are critical to the offense strategy of the team
Analysis of an Ex-Vessel Break in the ITER Divertor Cooling Loop
No full textIn the present work the integrated ECART code, developed for severe accident analysis in LWRs, is applied on the analysis of a
large ex-vessel break in the divertor cooling loop of the international thermonuclear experimental reactor (ITER).Acomparison of
the ECART results with those obtained by Studsvik Nuclear AB (S), utilizing the MELCOR code, was also performed in the general
framework of the quality assurance program for the ITER accident analyses. This comparison gives a good agreement in the
results, both for thermal-hydraulics and the environmental radioactive releases. Mainly these analyses, from the point of view of
the ITER safety, confirm that the accidental overpressure inside the vacuum vessel and theTokamak coolingwater system (TWCS)
Vault is always well below the design limits and that the radioactive releases are adequately confined below the ITER guidelines
Tritium and dust source term inventory evaluation issues in the European DEMO reactor concepts
No full textFusion reactors represent a future evolution of the nuclear technology improving the world-wide energy portfolio. The experimental fusion reactor under construction (ITER) and the planned industrial fusion reactors (DEMO) are large and complex facilities. For their operation it is necessary to ensure safety limiting of radiological and mobilizable source terms inventory, such as tritium and radioactive dust. The source term inventories shall be assumed in the establishment of operational and safety requirements for DEMO, as well as performing safety analyses for commercial fusion devices. In the last few years a methodology for evaluation of tritium and dust source term inventory has been proposed in the framework of the EUROFusion project. The basis of the methodology is a semi-empirical approach to scale the radioactive inventory limits implemented in ITER. The source term amounts derived for DEMO will supply a guidance for safe operation of future fusion reactors. The development of methodology has to be completed and refined because of the lack of validation versus adequate experimental data and rules for extension to different scenarios. The aim of this work is assessment of the developed methodology for evaluation of the source terms inventory versus JET operating limits for tritium and versus the dust control strategy adopted in ITER for the dust. The updating of the methodology for the dust and T inventory was carried out in line with the current DEMO design. The new values of the in-VV source terms were achieved. These values are recommended to be used for the safety assessment of the fusion reactor. Calculated DST and TST inventories’ values show a reasonable agreement with scaled ITER or assessed JET limits
Synthesis of electrical networks interconnecting PZT actuators to damp mechanical vibrations
No full textAnalysis of lockdown perception in the United States during the COVID-19 pandemic
Full text linkContainment measures have been applied throughout the world to halt the COVID-19 pandemic. In the United States, several forms of lockdown have been adopted in different parts of the country, leading to heterogeneous epidemiological, social, and economic effects. Here, we present a spatio-temporal analysis of a Twitter dataset comprising 1.3 million geo-localized Tweets about lockdown, from January to May 2020. Through sentiment analysis, we classified Tweets as expressing positive or negative emotions about lockdown, demonstrating a change in perception during the course of the pandemic modulated by socio-economic factors. A transfer entropy analysis of the time series of Tweets unveiled that the emotions in different parts of the country did not evolve independently. Rather, they were mediated by spatial interactions, which were also related to socio-ecomomic factors and, arguably, to political orientations. This study constitutes a first, necessary step toward isolating the mechanisms underlying the acceptance of public health interventions from highly resolved online datasets
Exploratory fire analysis in DONES lithium system
No full textThe exploitation of Nuclear Fusion energy in power plants will require the development and qualification of materials able to withstand outstanding neutronic loads for which no operating experience is currently available. Therefore, a Demo-Oriented early NEutron Source (DONES) facility for material irradiation is currently being designed within EUROfusion programme aimed at the production of neutrons with fusion relevant spectrum and fluence by means of D – Li stripping reactions occurring between a deuteron beam impacting a stable liquid lithium flowing film implementing the target. The Lithium System (LS) in DONES shall provide circulation of liquid lithium with suitable thermal-hydraulic characteristics and assure impurity control and heat removal. Given the hazard constituted by liquid lithium inventory and the potential risk of reactions with air eventually resulting into fire events, a preliminary evaluation of the modality of occurrence and evolution of such abnormal events in LS has been performed. In particular, two events have been selected for fire analysis. The first event considers a failure of off-line sampler equipment with water getting in contact with sampled lithium inventory. The initiating event is a failure in the glove box containing the off-line sampler. An air ingress occurs in the glovebox and a break of the Li flask is hypothesized at the same time. The second event assumes a leak at the outlet of the electromagnetic pump with loss of Lithium from the Li pipe in Heat Rejection System in LS room. Simultaneous air ingress is hypothesized as well in LS room (normally filled with inert argon). Fire loads were initially identified for the selected events and the room models developed considering dimensions, lithium inventory and fire compartment assumed to coincide with room limits. The ignition of lithium in contact with air occurs at liquid lithium operating temperature as reported in most conservative observations in literature and lithium fires were simulated as heat flux associated to lithium – air reactions rates observed in literature. A model for both events was implemented in Fire Dynamic Simulator (FDS) code to evaluate fire dynamics and a sensitivity analysis was performed on relevant inventories in the lithium loop area to investigate possible consequences
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