Behavioural modelling of physical systems from observations of their input/output behaviour is an important task in engineering. Such models are needed for fault monitoring as well as intelligent control of these systems. The paper addresses one subtask of behavioural modelling, namely the selection of input variables to be used in predicting the behaviour of an output variable. A technique that is well suited for qualitative behavioural modelling and simulation of physical systems is Fuzzy Inductive Reasoning (FIR), a methodology based on General System Theory. Yet, the FIR modelling methodology is of exponential computational complexity, and therefore, it may be useful to consider other approaches as booster techniques for FIR. Different variable selection algorithms: the method of the unreconstructed variance for the best reconstruction, methods based on regression coefficients (OLS, PCR and PLS) and other methods as Multiple Correlation Coefficients (MCC), Principal Components Analysis (PCA) and Cluster analysis are discussed and compared to each other for use in predicting the behaviour of a steam generator. The different variable selection algorithms previously named are then used as booster techniques for FIR. Some of the used linear techniques have been found to be non-effective in the task of selecting variables in order to compute a posterior FIR model. Methods based on clustering seem particularly well suited for pre-selecting subsets of variables to be used in a FIR modelling and simulation effort. ; The research reported in this article was made possible, thanks to a Ph.D. fellowship of the Ministry for Education and Culture from the Spanish Government funded within the frame of the TAP96-0882 project. ; Peer Reviewed
35 pages, 8 figures, 3 tables.-- Pre-print archive. ; A method for the asteroseismic analysis of beta Cephei stars is presented and applied to the star nu Eridani. The method is based on the analysis of rotational splittings, and their asymmetries using differentially-rotating asteroseismic models. Models with masses around 7.13 M_sun, and ages around 14.9 Myr, were found to fit better 10 of the 14 observed frequencies, which were identified as the fundamental radial mode and the three L=1 triplets g, p, and p. The splittings and aymmetries found for these modes recover those provided in the literature, except for p. For this last mode, all its non-axysimmetric components are predicted by the models. Moreover, opposite signs of the observed and predicted splitting asymmetries are found. If identification is confirmed, this can be a very interesting source of information about the internal rotation profile, in particular in the outer regions of the star. In general, the seismic models which include a description for shellular rotation yield slightly better results as compared with those given by uniformly-rotating models. Furthermore, we show that asymmetries are quite dependent on the overshooting of the convective core, which make the present technique suitable for testing the theories describing the angular momentum redistribution and chemical mixing due to rotationally-induced turbulence. ; JCS acknowledges support by the "Instituto de Astrofísica de Andalucía" by an I3P contract financed by the European Social Fund and from the Spanish "Plan Nacional del Espacio" under project ESP2007-65480-C02-01. PJA acknowledges financial support from a "Ramon y Cajal" contract of the Spanish Ministry of Education and Science. CRL acknowledges financial support from an "´ Angeles Alvariño" contract of the "Xunta de Galicia", local government. ; Peer reviewed
Open Access. Attribution 4.0 International (CC BY 4.0) ; This paper aims at being a provocative guide to the future of asteroseismology from the perspective of the analysis of time series, where the fundamentals of harmonic analysis are subjected to stress tests. In this context, we give an annotated summary of our research over the last decades on harmonic analysis of A-F stars. We discuss and explore the consequences of our findings, which may extend to any kind of pulsators. As well, we analyse the impact of this reconsideration on future asteroseismic studies, which would entail a paradigm shift. This includes a discussion on the presence of fractal behavior in delta Sct stars, and how this can be used to develop a stopping criterion of the pre-whitening process, as an alternative to SNR (or significance) criterion. Drilling a scientific paradigm has its natural resilience, hence the path described here is being arduous, although fruitful at the same time. ; SF, JP-G, JR, ML-M, and RG acknowledges financial support from the State Agency for Research of the Spanish MCIU through the Center of Excellence Severo Ochoa award for the Instituto de Astrofisica de Andalucia (SEV-2017-0709) and Spanish public funds for research under projects ESP2015-65712C5-5-R. JS and AG acknowledge funding support from Spanish public funds for research under projects ESP2017-87676-C5-2R. JS also acknowledges funding support from project RYC2012-09913 under the Ramon y Cajal program of the Spanish MINECO. AG acknowledges support from Universidad de Granada under project E-FQM-041-UGR18 from the Programa Operativo FEDER 2014-2020 programme by Junta de Andalucia regional Government. ; Peer reviewed