269 research outputs found
Performance limiting MHD phenomena in fusion devices: physics and active control
No full textIn this thesis different aspects of MagnetoHydroDynamic phenomena that limit plasma performance and confinement in toroidal pinch devices will be addressed.
The thesis contains original work carried out in two different devices: the Joint European Torus (JET) tokamak, and the RFX-mod Reversed Field Pinch (RFP), which are both the largest magnetic confinement devices in operation for their configuration.
In the JET device focus was put on Neoclassical Tearing Modes (NTMs), which are resistive instabilities that tear magnetic field lines and reconnect them forming magnetic field islands. With the aim of studying the NTM physics, two radial localization techniques for magnetic islands have been developed, and their outputs have been compared with q profiles obtained with a Motional Stark Effect diagnostic. One of the studied localization techniques has been also used in a non conventional way to reconstruct the NTM m number spectrum, and to extract new
information on the tearing-kink structure of the mode. The impact of NTMs on JET advanced tokamak discharges has been documented, with the ultimate aim of quantifying the loss in plasma confinement induced by the mode as a function of the island radial localization.
Other chirping modes were encountered in JET, which are thought to be driven by energetic particles and dubbed q=2 fishbones. Their experimental signature and impact on the plasma discharge have been studied.
In the RFX-mod device the addressed topic was the study and control of Resistive Wall Modes (RWMs) in RFP configuration. The RWM is a branch of the ideal kink mode that grows on the time scale of current diffusion in the wall.
First of all a RWM growth rate database in RFX-mod was created, and it was subsequently used as a standard growth rate reference in the analysis of the couplings between different m and n harmonics.
Advanced feedback control topics were addressed as well, such as the development and benchmark of a dynamical RWM control simulator, and the RWM stabilization in control experiments using various sets of active saddle coils.In questa tesi saranno affrontati i diversi aspetti dei fenomeni magnetoidrodinamici che limitano le prestazioni ed il confinamento degli esperimenti toroidali di tipo pinch.
La tesi contiene il lavoro originale portato avanti in due diverse macchine, che sono entrambe i più grandi esperimenti a confinamento magnetico in operazione per rispettive configurazioni: il tokamak Joint European Torus (JET) ed il Reversed Field Pinch (RFP) RFX-mod.
Nel tokamak JET l’attività di ricerca si è concentrata sui Neoclassical Tearing Modes (NTM), che sono delle instabilità resistive che rompono le linee di campo magnetico e le riconnettono, formando delle isole di campo magnetico. Allo scopo di studiare la fisica dei NTM, sono state sviluppate due tecniche per la localizzazione radiale delle isole magnetiche, ed i risultati prodotti sono stati confrontati con i profili radiali di q ottenuti per mezzo della diagnostica Motional Stark Effect.
Una delle tecniche di localizzazione studiate è stata anche usata in modo non convenzionale per ricostruire lo spettro del numero d’onda m poloidale dei NTM, e per ricavare informazioni sulla struttura kink-tearing di queste instabilità. E’ stato pure documentato l’impatto dei NTM sulle scariche advanced tokamak, allo scopo di quantificare il peggioramento nel confinamento del plasma che queste inducono, in funzione della localizzazione radiale dell’isola magnetica da loro generata.
Durante l’attività su JET sono state incontrate anche delle altre instabilità, che si ritiene siano eccitate dalla popolazione di particelle veloci nel plasma, e che sono soprannominate fishbone q = 2. Sono state caratterizzate le loro evidenze sperimentali ed il loro impatto sugli impulsi di plasma.
Nel RFP RFX-mod il lavoro è stato concentrato sullo studio e controllo dei Resistive Wall Modes (RWM), che sono una branca dei modi kink ideali che cresce selle scale dei tempi della diffusione delle correnti all’interno delle strutture conduttrici attorno al plasma.
Inizialmente è stato creato un database contenente i tassi di crescita di tutte le instabilità di tipo RWM rilevate in RFX-mod, ed il database è stato in seguito usato come riferimento nell’analizzare gli accoppiamenti tra le diverse armoniche m ed n dei RWM.
Sono stati affrontati anche problemi di controllo in feedback avanzato, come lo sviluppo ed il benchmark di un simulatore dinamico del controllo attivo RWM, e la sperimentazione del controllo RWM usando diversi gruppi di bobine attive
N2BPC: an algorithmic approach from Networks to Bacteria's metabolite Production and Consumption
No full textMicroorganisms tend to coexist and form complex relationships between themselves and the environment they inhabit. The development of increasingly efficient and cost-effective high-throughput 16S rDNA-seq techniques has enhanced the possibility of studying the networks of interactions and understanding the drivers of a bacteria community organization. Many network inference methods have been developed to answer this open question; however, the lack of a known biological truth makes it difficult to validate the results obtained.
Therefore, in silico solutions are needed to simulate realistic gold standards. In this work, we propose N2BPC, an algorithmic approach that, starting from a known weighted and directed network topology assumed to be the ground truth for microbial interactions, generate the consumer preferences (C) and metabolic rules (D) of a Microbial Consumer Resource Model (MiCRM) for simulating bacteria community.
N2BPC models microbial interactions as metabolites that are consumed by the target nodes of every edge, and ensure the uniqueness of the generated C and D
Recensione di Matteo Santipolo, Educazione e politica linguistica. Teoria e pratica, Roma, Bulzoni, 2022
No full textRecensione del volume "Educazione e politica linguistica. Teoria e pratica
Inferring microbial ecological networks from metagenomics data, when should we trust the results?
No full textLimitations of the co-occurrence-based approach in the inference of microbiota interaction networks.
No full text
Biologically Informed procedure for Feature Summarization in Spatial Transcriptomics
No full textModern machine learning approaches have shown remarkable success in extracting patterns from high-dimensional biological data. However, when applied to spatial transcriptomics, these methods face significant challenges due to the sparsity of spatially resolved measurements and the complex, nonlinear relationships between molecular features.
To address these challenges, we propose a procedure that integrates single-cell and spatial transcriptomics by considering biologically meaningful regulatory factors as an interpretable feature space. These factors act as latent variables that encode transcriptional programmes, reducing dimensionality and preserving mechanistic relevance.
This approach improves interpretability by shifting from raw gene expression to a structured representation of regulatory activity, providing a scalable and biologically interpretable framework for spatial transcriptomic analysis
Control system optimization techniques for real-time applications in fusion plasmas: the RFX-mod experience
No full textSimulation of bacteria interaction networks: from topology to species abundances
No full textBackground: Microorganisms frequently coexist and establish complex relationships within their environments. Recent advancements in high-throughput 16S rDNA sequencing techniques have significantly improved our capacity to explore the factors that influence bacterial community organization. However, despite the development of numerous inference methods, the lack of a well-established biological truth presents challenges in validating the obtained results. Therefore, in-silico solutions are critical for simulating realistic gold standards. Methods: We introduce N2SIMBA, a modular algorithmic approach that begins with a known weighted and directed network topology, which is assumed to represent the true nature of microbial interactions. This network serves as a foundation to generate the rules of a Microbial Consumer Resource Model (MiCRM) based on the framework established by Goldford et al. (2018). This model describes the bacterial community characterized by these interactions through a set of Ordinary Differential Equations (ODEs). The subsequent sequencing process is simulated using metaSPARSim as described by Patuzzi et al. (2019). Results: N2SIMBA forms the core component of a systematic framework that allows for the assumption of a gold standard bacterial interaction network and enables the simulation of bacterial community evolution driven by these interactions under varying environmental conditions. The results indicate that, in a resource-rich environment, the bacterial community stabilizes to a relative count distribution similar to the topology of the assumed bacteria interaction network, thereby promoting community resilience and growth. Conversely, a resource-poor environment limits the survival of species the survival of species to those that are highly interconnected within the assumed interaction network. Conclusions: N2SIMBA significantly enhances our understanding of bacterial community organization, providing valuable tools for investigating hypotheses in-silico and evaluating methodologies for inferring bacterial interactions
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