102,121 research outputs found
Covariance matrix estimation of the maximum likelihood estimator in multivariate clusterwise linear regression
No full textThe expectation-maximisation algorithm is employed to perform maximum likelihood estimation in a wide range of situations, including regression analysis based on clusterwise regression models.A disadvantage of using this algorithm is that it is unable to provide an assessment of the sample variability of the maximum likelihood estimator. This inability is a consequence of the fact that the algorithm does not require deriving an analytical expression for the Hessian matrix, thus preventing from a direct evaluation of the asymptotic covariance matrix of the estimator. A solution to this problem when performing linear regression analysis through a multivariate Gaussian clusterwise regression model is developed. Two estimators of the asymptotic covariance matrix of the maximum likelihood estimator are proposed. In practical applications their use makes it possible to avoid resorting to bootstrap techniques and general purpose mathematical optimisers. The performances of these estimators are evaluated in analysing small simulated and real datasets; the obtained results illustrate their usefulness and effectiveness in practical applications. From a theoretical point of view, under suitable conditions, the proposed estimators are shown to be consistent
New insights on the painting “Portrait of Mario Nuzzi”: a preliminary analytical study of Mario Nuzzi’s pictorial production and of his artistic collaborations
No full textThe study and characterization of an art work carried out by two or more artists is always an interesting challenge since each painter, although belonging to the same artistic current, can introduce specific pictorial materials or peculiar aesthetic effects, which constitute the artist fingerprint. This work presents a preliminary analytical study of the “Portrait of Mario Nuzzi”, painted by Giovanni Maria Morandi and Mario Nuzzi. In particular, non-invasive investigations were conducted using UV–VIS–NIR–SWIR multispectral imaging, radiography and X-ray spectroscopy (XRF). Multivariate analyses (PCA) were performed on VIS–NIR multispectral imaging in order to highlight some details not clearly visible using a traditional univariate analysis. Such an approach could be useful for authentication processes. In particular, in this paper we propose the use of the score density plot to determine the artist’s “chiaroscuro” fingerprint. Finally, the artist’s palette was compared with that of the “Primavera” painting, painted by Mario Nuzzi and Filippo Lauri, by using XRF analyses. We discovered that “Portrait of Mario Nuzzi” has not been significantly changed since the final version. Furthermore, the elemental composition of the pigments revealed that the palette used in the two paintings does not completely overlap. This aspect encourages us to perform a more detailed analysis of the pigments with the aim of better discriminating the parts painted by Mario Nuzzi from those of each collaborator
Dacriocistorinostomia e chirurgia endoscopica nel trattamento delle patologie delle basse vie lacrimali
No full text
The weaning practices: A new challenge for pediatricians?
No full textIntroduction of complementary feeding, or weaning, is the period where infants are gradually introduced to solid foods, with a progressive reduction of breastfeeding or bottle-feeding. Weaning represents a crucial nutritional moment in the growth and development of infants, and it can also affect future health. Throughout the years, various weaning strategies have been proposed, ranging from classic to baby-led weaning. Recently, vegetarian-/vegan-based approaches are also being increasingly adopted by young parents. This rostrum aims to critically address the safety profiles of current weaning practices for infants and to highlight the important role of pediatricians in choosing the most advisable weaning approach for their patients
Aspetti nutraceutici delle fragole : indagini sul contenuto in acido ascorbico
No full textTwenty fruit samples of 36 cvs and 16 selections grown at Cesena, Boves and Verona from 1994 to 2001 were assayed for the ascorbic acid content. Results showed a wide range of ascorbic acid content, from 20 to 100 mg/100 g f.w., according to the cultivars. Factors such as growing location, year of production and short term storage were also studied, showing large effects on ascorbic acid content
Misura delle fasi del passo tramite telecamera time-of-flight durante camminate assistite da esoscheletro robotico in ambiente esterno
No full textLa perdita della capacità di deambulazione è una delle principali conseguenze dovute a lesioni alla colonna vertebrale. Negli ultimi anni si è assistito ad uno sviluppo sempre maggiore di esoscheletri per gli arti inferiori che permettono ad utilizzatori paraplegici di tornare a camminare. L’utilizzo di questi esoscheletri, soprattutto durante la fase di training iniziale, è purtroppo spesso limitato all’interno di laboratori specializzati muniti di diversi tipi di trasduttori per l’analisi della cinematica e della dinamica della camminata assistita (sistemi di visione, accelerometri, piattaforme di forza, etc.).
Per superare queste limitazioni sono state sviluppate delle stampelle strumentate in grado, attraverso un adeguato modello biomeccanico, di valutare i carichi agenti sugli arti superiori misurando il carico scambiato tra stampella e piano d’appoggio della stessa, senza l’utilizzo di altro tipo di strumentazione. Tramite questa analisi, il fisioterapista è in grado di valutare la qualità della camminata del paziente diminuendo in questo modo rischi di lesioni agli arti superiori dovute all’utilizzo dell’esoscheletro. Il grosso vantaggio del dispositivo sviluppato risiede nel fatto che si presta particolarmente bene per un utilizzo in un ambiente esterno, più naturale e, in generale, più favorevole per l’utilizzatore.
Il presente lavoro descrive un ulteriore sviluppo apportato alle stampelle strumentate appena descritte. L’obiettivo principale è quello di riuscire a misurare, assieme ai carichi agli arti superiori già possibile nella presente versione, anche le principali fasi della camminata (fase di stance, cioè piede appoggiato a terra, e fase di swing, cioè piede alzato da terra) in modo da fornire al fisioterapista un ulteriore grandezza correlata alla qualità del training del paziente. Il sistema di misura sviluppato sfrutta un approccio basato su tecniche di machine learning: una prima acquisizione viene effettuata per allenare il modello predittivo (fase di training), il quale viene poi utilizzato nelle restanti acquisizioni per predire la macro fase del passo in cui si trova ogni piede del paziente (fase di predizione)
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