638 research outputs found
Development of 2D/3D equilibrium codes for magnetically confined fusion experiments
No full textThe present work is the result of a three-year Ph.D. research project carried out at Consorzio RFX on magnetically confined plasmas. Research on controlled thermonuclear fusion is currently being pursued by many countries throughout the world, thanks to its promise of a relatively clean and abundant energy source. The next steps for the international community are the construction and operation of a large device, ITER, considered as the last fusion physics experiment with respect to the tokamak configuration. After ITER, in fact, the first commercial proto-reactor, DEMO, is envisaged to demonstrate the feasibility of fusion as an energy source. The stellarator community, on the other hand, is building a new device, Wendelstein 7-X, which will provide further insight into three-dimensional physics.
Among the various fusion devices, the reversed-field pinch has been demonstrated, if not a viable device for commercial energy production, an excellent tool for plasma physics studies. The RFX-mod experiment situated at Consorzio RFX in Padova, Italy, is the biggest RFP device in the world and the most advanced fusion device with respect to active stabilization of magnetohydrodynamic perturbations through feedback control. The RFX-mod team, further-more, has tackled first theoretically and then experimentally the paramount concept of self-organization in RFPs, which produces enhanced confinement regimes with better transport properties and reduced magnetic chaos. Resonant tearing modes are known to be the biggest players in the dynamo mechanisms responsible for the helically deformed and enhanced regimes.
In such a complex framework, the reconstruction of the tearing modes in-side the plasma through external measurements is extremely important for both modelling and experimental reasons since, for example, the structures influencing the core transport properties of plasmas are in part linked to tearing modes.
The present Ph.D. thesis focuses, in particular, on the development of two-and three-dimensional equilibrium codes. As a first problem, a Fortran algorithm has been developed for the numerical solution of the helical Grad-Shafranov equation, which is a two-dimensional equilibrium equation derived under the assumption of helical symmetry. Such assumption is found to be particularly appropriate for the study of the dominant tearing mode in RFX-mod during routine quasi-single-helicity phases in RFP shots, but it can be applied to tokamak shots as well.
As a second problem, the three-dimensional VMEC/V3FIT code suite for equilibrium reconstruction has been analysed and studied. The helical Grad-Shafranov solver has been tested against the three-dimensional VMEC/V3FIT predictions, carrying out a valuable benchmark. Then, a further step has been taken in the application of the V3FIT code to fixed-boundary reconstructions in RFX-mod by implementing a new virtual diagnostic, which had been previously demonstrated to be able to solve the mismatch in the edge value for the helical safety factor
Case studies of interpretable machine learning in astrophysics
No full textn this work, variable stars (especially RR Lyrae) light curves and the pursuit of Intermediate Mass Black Holes (IMBHs) within globular clusters (GCs), are explored through a data-driven approach using interpretable machine learning (ML) techniques.
We initiate the study with the development of an inherently interpretable classifier, utilizing L1 penalization to induce simplicity through sparsity in the model. This approach ensures a straightforward interpretation of astronomical data, providing a transparent model that facilitates the extraction of valuable insights. This penalized classifier, which reaches sparsity in the light-curve features, with a limited trade-off in accuracy performs well both on the Catalina Sky Survey validation set and, remarkably, also on the different ASAS/ASAS-SN light curve test set.
Following this, we apply the Sparse Identification of Nonlinear Dynamics (SINDy) algorithm to analyze light curves of RR Lyrae and Scuti stars, uncovering the underlying dynamical systems from observational light curves from the Catalina Sky Survey. This method yields a sparse and interpretable representation. The success rate depends systematically on variable type, with possible implications for variable star classification; however it does not obviously depend on amplitude or period. Successful models can be reduced to the generalized Lienard equation . For the equation can be solved exactly, and it admits both periodic and non-periodic solutions. We find a condition on the coefficients of the general equation for the presence of a limit cycle, which is also observed numerically in several instances.
In addition, we employ Dynamic Mode Decomposition (DMD) to investigate the modes of variable stars within the Omega Centauri cluster. This data-driven technique provides insights into the diverse modes of stellar variability, contributing to our understanding of the complex dynamics of these stars.
In the context of IMBH detection in GCs, we apply two ML models: CORELS, an inherently interpretable model, and XGBoost, a black box model elucidated post hoc using local, model-agnostic explanation rules known as anchors. By training these models on simulated GC data and subsequently applying them to actual observational data, we emphasize the importance of interpretability in scientific investigations. Our results demonstrate that simpler, interpretable models can indeed attain accuracy comparable to their more complex counterparts (for the relevant metrics), an approach of significant importance in the field of astronomy where comprehending the model’s decision-making process is crucial for establishing trust and facilitating further scientific exploration for domain-field experts.
Our findings challenge the prevalent assumption that complexity is a necessary condition for accuracy, highlighting the existence of interpretable models within the set of accurate predictive models.
In the domains of variable stars and identifying intermediate-mass black holes within globular clusters, we demonstrate that the application of machine learning tools can be both reliable and insightful when guided by models that are both interpretable and straightforward.
This aligns with the immediate call for transparency and human-understandability in ML applications, extending beyond astronomy and into the broader scientific community
Piero Sraffa and His Books – a foreword to the Catalogue of his inimitable library
No full textThis foreword gives a preview of the sort of books Piero Sraffa collected, specifying the criteria that appear to have been used for the selection. The Author of this foreword is convinced that the discovery of these criteria may help to understand the basis of the type of history of economic thought that Piero Sraffa had in mind
Measuring the spectral index of turbulent gas with deep learning from projected density maps
No full textTurbulence plays a key role in star formation in molecular clouds, affecting star cluster primordial properties. As modelling present-day objects hinges on our understanding of their initial conditions, better constraints on turbulence can result in windfalls in Galactic archaeology, star cluster dynamics, and star formation. Observationally, constraining the spectral index of turbulent gas usually involves computing spectra from velocity maps. Here, we suggest that information on the spectral index might be directly inferred from column density maps (possibly obtained by dust emission/absorption) through deep learning. We generate mock density maps from a large set of adaptive mesh refinement turbulent gas simulations using the hydro-simulation code RAMSES. We train a convolutional neural network (CNN) on the resulting images to predict the turbulence index, optimize hyperparameters in validation and test on a holdout set. Our adopted CNN model achieves a mean squared error of 0.024 in its predictions on our holdout set, over underlying spectral indexes ranging from 3 to 4.5. We also perform robustness tests by applying our model to altered holdout set images, and to images obtained by running simulations at different resolutions. This preliminary result on simulated density maps encourages further developments on real data, where observational biases and other issues need to be taken into account
Biomassbed: a biological system to reduce pesticide point contamination at farm level
No full textA potential method for cleaning water from point-source pollution by organic compounds is using biological reactors. In this study, four reactors were tested for their ability to retain and degrade pesticides. The pesticides tested were the insecticide chlorpyrifos, the fungicide metalaxyl and the herbicide imazamox. The reactors were filled with differing mixtures of vine-branch, citrus peel, urban waste and public green compost. The reactor volume was 188 1. Forced circulation of the contaminated solution was programmed to decontaminate the solution. Both retention and degradation of the compounds by the reactors was studied.Chlorpyrifos was the best retained, due to its physico-chemical characteristics, while only one substrate effectively retained metalaxyl and imazamox (citrus peel + urban waste compost). Degradation of the pesticides in the reactors was faster than published values for degradation in soil. The half-life of all pesticides in the reactors was less than 14 days, compared to literature values of 60-70 days in soil. The combined retention and fast degradation make the biofilter a feasible technique to reduce spill-related and point environmental contamination by pesticides. The technique is most effective against persistent pesticides, while for mobile pesticides, the efficiency can be improved with several passages of the contaminated solution through biofilters
Angelo Piero Cappello, Gabriele d’Annunzio. Luigi Pirandello. Cordialissimi nemici, Pescara, Ianieri edizioni, 2024
No full textPiero Vignozzi, o dell'impronta residua
No full textThe author considers the tendency in the d'après by Piero Vignozzi to elide elements of well-known works by old masters, and concludes that we are seeing a reflection of Robert Rauschenberg's Erased de Kooning Drawing
Esserci e temporalità ne «La figlia di Babilonia» di Piero Bigongiari
No full textBeing there and temporality in La figlia di Babilonia of Piero Bigongiari · In this paper the author takes on Piero Bigongiari’s book of poetry La figlia di Babilonia (1942) by means of the categories of being-there and temporality by Martin Heidegger. Through an analysis of the Tuscan poet’s essays and interviews and foremost through the most important texts of this book poetry, the author shows how hermetic poetic is deeply rooted in the diffusion of German existentialism in Ital
Il Ponte di Piero Calamandrei
No full textThe paper traces the history of the journal Il Ponte, founded by Piero Calamandrei in April 1945, in order to capture the ideal roots of this audacious publishing initiative. The Author focuses on the liberal-socialist vocation of the journal and on the ideals of European federalism that led Calamandrei to oppose the Atlantic Pact. Lastly, he delves into the commitment of the Florentine jurist in support of the Constitution, democracy and the Welfare State
Oratione di m. Piero Vettori in lode di Massimiliano ij. imperadore, morto : recitata nella chiesa di San Lorenzo, il di xij. di nouembre, M D LXXVI /
No full textT.p. woodcut with Medici arms impaling Austria. Two historiated initials.Mode of access: Internet.At upper left-hand corner of front pastedown is bookplate of Giacomo Manzoni (Gelli 636).Binding: 19th-century pebble-grained red cloth. Red goatskin spine with author, title, and imprint in gilt. Leaves numbered 206-217 in black ink at upper right-hand corner of rectos, implying that the work was formerly bound as part of a larger vol
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