Michela Gelfusa

Michela Gelfusa
University of Rome Tor Vergata | UNIROMA2

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54
Publications
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254
Citations

Publications

Publications (54)
Article
In many areas of research, from neuro-biology to nuclear fusion, which investigate complex dynamical systems involving numerous, different and interconnected physical quantities, the application of advanced analysis tools based on Chaos theory and Information theory has provided significant improvements both by supporting theoretical models and by...
Article
Full-text available
The high confinement mode (H-mode) is considered the optimal regime for the production of energy through nuclear fusion for industrial purposes since it allows to increase the energy confinement time of the plasma roughly by a factor of two. Consequently, it has been selected at the moment as the standard scenario for the next generation of devices...
Article
Full-text available
The Stellarator is a magnetic configuration considered a realistic candidate for a future thermonuclear fusion commercial reactor. The most widely accepted scaling law of the energy confinement time for the Stellarator is the ISS04, which employs a renormalisation factor, fren, specific to each device and each level of optimisation for individual m...
Article
The recent experience of metallic devices, operating in ITER relevant regions of the operational space, has shown that the disruptivity of these plasmas is unacceptably high. The main causes of the disruptions are linked to impurity accumulation in the core and edge cooling, resulting in unstable current profiles. Avoidance and prevention of the co...
Article
Bolometric tomography is a widely applied technique to infer important indirect quantities in magnetically confined plasmas, such as the total radiated power. However, being an inverse and ill-posed problem, the tomographic algorithms have to be carefully steered to converge on the most approriate solutions and often specialists have to balance the...
Article
On the route to the commercial reactor, the experiments in Magnetically Confinement Nuclear Fusion have become increasingly complex and they tend to produce huge amounts of data. New analysis tools have therefore become indispensable, to fully exploit the information generated by the most relevant devices, which are nowadays very expensive to both...
Article
Full-text available
Model selection criteria are widely used to identify the model that best represents the data among a set of potential candidates. Amidst the different model selection criteria, the Bayesian information criterion (BIC) and the Akaike information criterion (AIC) are the most popular and better understood. In the derivation of these indicators, it was...
Article
Full-text available
Understanding and quantifying the mutual influence between systems remain crucial but challenging tasks in any scientific enterprise. The Pearson correlation coefficient, the mutual information, and the information quality ratio are the most widely used indicators, only the last two being valid for nonlinear interactions. Given their limitations, a...
Article
Full-text available
The early detection of fire is one of the possible applications of LiDAR techniques. The smoke generated by a fire is mainly compounded of CO2, H2O, particulate, and other combustion products, which involve the local variation of the scattering of the electromagnetic wave at specific wavelengths. The increases of the backscattering coefficient are...
Article
Nowadays, disruption predictors, based on machine learning techniques, can perform well but they typically do not provide any information about the type of disruption and cannot predict the time remaining before the current quench. On the other hand, the automatic identification of the disruption type is a crucial aspect required to optimize the re...
Article
Full-text available
Disruptions in tokamaks are very often associated with the slowing down of magneto-hydrodynamic (MHD) instabilities and their subsequent locking to the wall. To improve the understanding of the chain of events ending with a disruption, a statistically robust and physically based criterion has been devised to track the slowing down of modes with tor...
Article
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The inadequacies of basic physics models for disruption prediction have induced the community to increasingly rely on data mining tools. In the last decade, it has been shown how machine learning predictors can achieve a much better performance than those obtained with manually identified thresholds or empirical descriptions of the plasma stability...
Article
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Advanced time series analysis and causality detection techniques have been successfully applied to the assessment of synchronization experiments in tokamaks, such as Edge Localized Modes (ELMs) and sawtooth pacing. Lag synchronization is a typical strategy for fusion plasma instability control by pace-making techniques. The major difficulty, in eva...
Article
Full-text available
The Bayesian information criterion (BIC), the Akaike information criterion (AIC), and some other indicators derived from them are widely used for model selection. In their original form, they contain the likelihood of the data given the models. Unfortunately, in many applications, it is practically impossible to calculate the likelihood, and, there...
Article
Full-text available
The increasingly sophisticated investigations of complex systems require more robust estimates of the correlations between the measured quantities. The traditional Pearson correlation coefficient is easy to calculate but sensitive only to linear correlations. The total influence between quantities is, therefore, often expressed in terms of the mutu...
Article
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The application of data driven machine learning and advanced statistical tools to complex physics experiments, such as Magnetic Confinement Nuclear Fusion, can be problematic, due the varying conditions of the systems to be studied. In particular, new experiments have to be planned in unexplored regions of the operational space. As a consequence, c...
Conference Paper
Full-text available
The increasingly sophisticated investigations of complex systems require more robust estimates of the correlations between the measured quantities. The traditional Pearson Correlation Coefficient is easy to calculate but is sensitive only to linear correlations. The total influence between quantities is therefore often expressed in terms of the Mut...
Article
Full-text available
In the last years the reputation of medical, economic, and scientific expertise has been strongly damaged by a series of false predictions and contradictory studies. The lax application of statistical principles has certainly contributed to the uncertainty and loss of confidence in the sciences. Various assumptions, generally held as valid in stati...
Article
Full-text available
Malaria, a disease with major health and socio-economic impacts, is driven by multiple factors, including a complex interaction with various climatic variables. In this paper, five methods developed for inferring causal relations between dynamic processes based on the information encapsulated in time series are applied on cases previously studied i...
Article
For many years, machine learning tools have proved to be very powerful disruption predictors in tokamaks. On the other hand, the vast majority of the techniques deployed assume that the input data is independent and is sampled from exactly the same probability distribution for the training set, the test set and the final real time deployment. This...
Article
Full-text available
A new measure for the characterization of interconnected dynamical systems coupling is proposed. The method is based on the representation of time series as weighted cross-visibility networks. The weights are introduced as the metric distance between connected nodes. The structure of the networks, depending on the coupling strength, is quantified v...
Article
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Understanding the details of the correlation between time series is an essential step on the route to assessing the causal relation between systems. Traditional statistical indicators, such as the Pearson correlation coefficient and the mutual information, have some significant limitations. More recently, transfer entropy has been proposed as a pow...
Article
Full-text available
The development and improvement of techniques to monitor off-normal concentrations of chemicals in the atmosphere are crucial to guarantee human and environmental health, safety, and security. An interesting technique for use in research activities is the differential absorption lidar (DIAL); an improvement of the lidar technique able to provide in...
Article
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The total emission of radiation is a crucial quantity to calculate the power balances and to understand the physics of any Tokamak. Bolometric systems are the main tool to measure this important physical quantity through quite sophisticated tomographic inversion methods. On the Joint European Torus, the coverage of the bolometric diagnostic, due to...
Article
Detecting disruptions with sufficient anticipation time is essential to undertake any form of remedial strategy, mitigation or avoidance. Traditional predictors based on machine learning techniques can be very performing, if properly optimised, but do not provide a natural estimate of the quality of their outputs and they typically age very quickly...
Article
Full-text available
Modern experiments in Magnetic Confinement Nuclear Fusion can produce Gigabytes of data, mainly in form of time series. The acquired signals, composing massive databases, are typically affected by significant levels of noise. The interpretation of the time series can therefore become quite involved, particularly when tenuous causal relations have t...
Conference Paper
Full-text available
Considering the increase of atmospheric pollution levels in our cities, due to emissions from vehicles and domestic heating, and the growing threat of terrorism, it is necessary to develop instrumentation and gather know-how for the automatic detection and measurement of dangerous substances as quickly and far away as possible. The Multi-Wavelength...
Article
In metallic machines ICRH heating is playing an increasingly important role. One of its most recent applications on the Joint Europena Torus (JET) is sawtooth control by ICRH modulation, for avoiding triggering dangerous neo-classical tearing modes (NTMs) and counteracting impurity accumulation. Some of the main difficulties of these experiments ar...
Article
In recent years, the limitations of scalings in power-law form that are obtained from traditional log regression have become increasingly evident in many fields of research. Given the wide gap in operational space between present-day and next-generation devices, robustness of the obtained models in guaranteeing reasonable extrapolability is a major...
Poster
Full-text available
The increasing level of air pollution in our cities due to emissions from factories, vehicles and domestic heating, combined with the growing threat of terrorism, requires finding equipment and know-how that are useful to detect and monitor hazardous substances and their dispersion into the atmosphere as quickly and far away as possible. LiDAR/DIAL...
Chapter
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The increasing level of air pollution in our cities due to emissions from fac-tories, vehicles and domestic heating, combined with the growing threat of terrorism, requires finding equipment and know-how that are useful for the detection and monitoring of hazardous substances and their dispersion into the atmosphere as quickly and far away as possi...
Article
Full-text available
Urban air pollution causes deleterious effects on human health and the environment. To meet stringent standards imposed by the European Commission, advanced measurement methods are required. Remote sensing techniques, such as light detection and ranging (LiDAR), can be a valuable option for evaluating particulate matter (PM), emitted by vehicles in...
Conference Paper
The paper describes the project “Integrated technologies for fire monitoring and first alert” proposed by the authors to satisfy technical requirements of the Firefighter Bodies with particular attention to the monitoring of wood fires and release of chemical materials. The target system is composed of three sub-systems: sensors to detect target pa...
Conference Paper
Conformal predictors, currently applied to many problems in various fields determine precise levels of confidence in new predictions on the basis only of the information present in the past data, without making recourse to any assumptions except that the examples are generated independently from the same probability distribution. In this paper, the...
Conference Paper
Nowadays the intentional diffusion in air (both in open and closed environments) of chemical and biological contaminants presents a dramatic risk for the health of the public worldwide. The needs of a high-tech network composed by diagnostics, software, decision support systems and cyber security tools are urging all the stakeholders (military, pub...
Article
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Biosecurity and biosafety are key concerns of modern society. Although nanomaterials are improving the capacities of point detectors, standoff detection still appears to be an open issue. Laser-induced fluorescence of biological agents (BAs) has proved to be one of the most promising optical techniques to achieve early standoff detection, but its s...
Conference Paper
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Ebola, Armi di Distruzioni di Massa, Terrorismo, ISIS, Fukushima e minacce globali. I media ci aggiornano quotidianamente sui danni causati dal rilascio e la diffusione accidentale/naturale o volontaria di agenti pericolosi per l’uomo e l’ambiente circostante. È ben noto che la risoluzione degli eventi critici causati da tali fenomeni comportano im...
Conference Paper
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Chemical Warfare Agents, Biological Warfare Agents, Toxic Industrial Materials, Toxic Industrial Components. In questi anni il gruppo di ricerca di Elettronica Quantistica e Plasmi dell’Università di Tor Vergata ha realizzato dei dimostratori per la rivelazione ed identificazione delle sostanze chimiche sopra citate. Inoltre, sta mettendo a punto u...
Article
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Given the urgent need to converge on precise guidelines for accident management in nuclear fusion plants, an experimental campaign has been carried out on the “STARDUST-Upgrade” facility for dust mobilization phenomena investigation at the University of Rome Tor Vergata. The main purpose of this preliminary work was to test the “STARDUST-Upgrade” f...
Article
Full-text available
Biohazards represent an important issue in the field of security, both for the destructive potential and the psychological, economic and social impact that the use of biological agents for biowarfare could have on populations. Early identification of an intentional biological event is essential to ensure correct management and response to the emerg...
Article
Full-text available
Development of new technologies for Biological Warfare Agents (BWA) stand-off detection implies several safeties, logistic and economic drawbacks that involve production of different highly virulent bacteria and viruses, their isolation and characterization under adequate bio-containment and sample preparation for each agent to evaluate the testing...
Article
Air leakage into tokamaks vacuum vessel during plasma burning or maintenance operations may lead to the fast pressurization of the vacuum vessel. A fraction of the dust inventory present in the vacuum vessel can be mobilized threatening the safety of staff and workers on site, the local population and the environment. A numerical analysis of the ph...

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