589 research outputs found
Contributions to dependent processes in Bayesian nonparametrics
No full textRandom measures represent the fundamental building blocks for defining flexible priors in Bayesian nonparametric models. Over the last three decades, there has been a widespread diffusion of proposals aimed at introducing dependence among different random measures, in order to properly account for various forms of heterogeneity in the observations while preserving the possibility to borrow information across them.
The first part of the thesis focuses on vectors of dependent random measures defined through hierarchical structures, arguably the most natural and popular strategy to specify nonparametric priors for partially exchangeable data. These prior processes induce a random nested partition structure on the observations, which is usually taken into account by introducing additional latent variables. In this work, we propose a unified approach to hierarchies of random measures, in which such latent variables are directly inserted into the generative model for the data; within this framework, we identify a common structure shared by different hierarchical constructions proposed in the literature, and highlight a key identity which plays a prominent role in the derivation of quantities of interest. Furthermore, we consider hierarchical completely random measures as mixing measures to define dependent mixture hazard rates, which are in turn employed in the context of survival analysis to model competing risks data. We derive analytical results for Bayesian inference and prediction, as well as efficient posterior sampling algorithms; the effectiveness of our proposal is tested on simulated and clinical datasets.
The second part of the thesis contributes to the Bayesian nonparametric regression framework, by introducing a collection of dependent random probability measures indexed by covariates, which enter the model specification through a multiplicative kernel structure. This construction induces a predictor-dependent random partition model, characterized by great flexibility and inherent consistency for new observations, while retaining some analytical tractability. A noteworthy example arises when the distribution of such random measures is a transformation of the distribution of a stable process; moreover, the structure of the posterior distribution implied by such specification suggests the introduction of a novel nonhomogeneous process, which extends the two-parameter Poisson-Dirichlet process and acts as quasi-conjugate prior for our proposal. In the last chapter, we further develop this novel nonparametric process in the exchangeable setting, and characterize its prior-posterior updating mechanism, as well as its predictive structure
La Staffetta di Monte Sole. Un percorso sonoro alla scoperta della vita prima dell’eccidio
No full textLa Staffetta di Monte Sole è una passeggiata sonora permanente che consente ai visitatori del Parco
storico di Monte Sole di scoprire la storia del posto, partendo da una narrazione audio da ascoltare
mentre si cammina lungo il percorso della memoria. Una guida, accessibile direttamente dal proprio
smartphone, che racconta la vita prima dell’eccidio che colpì la comunità di Monte Sole. Un eccidio
che Francesca Candioli e Claudio Spanò, due ricercatori di storie, hanno provato a raccontare sottoforma di podcast interattivo concentrandosi in particolare sulla vita prima della strage.The Voices of Monte Sole is a permanent sound walk that allows all visitors to the Monte Sole Historical Park
to discover the history of the place, starting from a sound narration, to be listened to while walking along the
path of memory. A guide, accessible directly from your smartphone, which tells the life before the massacre that
struck the community of Monte Sole, in the heart of the Bolognese Appennino, between 29 September and 5
October 1944. A massacre that Francesca Candioli and Claudio Spanò, two story researchers, tried to tell in the
form of an interactive podcast focusing in particular on life before the massacre
A unified approach to hierarchical random measures
No full textHierarchical models enjoy great popularity due to their ability to handle heterogeneous groups of observations by leveraging on their underlying common structure. In a Bayesian nonparametric framework, the hierarchy is introduced at the level of group-specific random measures, and then translated to the observations’ level via suitable transformations. In this work, we propose a new strategy to derive closed-form expressions for the marginal and posterior distributions of each group. Indeed, by directly inserting a suitable set of latent variables into the generative model for the data, we unravel a common core shared by the different hierarchical constructions proposed in the Bayesian nonparametric literature. Specifically, we identify a key identity that underlies these models and highlight its role in the derivation of quantities of interest
Design responsabile per la robotica
No full textE' opinione comune che la robotica, in particolare quella di servizio, avrà un posto di rilievo negli investimenti sulla ricerca competitiva del prossimo futuro e che l'interdisciplinarietà delle competenze che vi parteciperanno giocherà un ruolo fondamentale per l'accettazione dei robot da parte dell'uom
Epicardial fat and liver stiffness by ARFI elastography in people living with Human Immunodeficiency Virus type 1 (HIV-1) infection without liver disease
No full textObjective: To evaluate the association between increased epicardial fat thickness (EFT) and liver stiffness measurement (LSM), as assessed by elastography in people with human immunodeficiency virus type 1 (HIV-1) infection (PWH) Methods: Ninety-one PWH on effective antiretroviral treatment (ART) were enrolled.EFT was measured by transthoracic echocardiography.Liver steatosis was evaluated by ultrasound Hamaguchi criteria and LSM by elastography with acoustic radiation force impulse (ARFI) technique.LSM ≥8 kPa was suggestive of clinically relevant fibrosis.Results: Mean age was 54.3 years and 27.5% were women.EFT correlated with HIV-1 infection duration (rS 0.252, P = 0.016), age at study entry (rS 0.527, P < 0.001), BMI (rS 0.363, P < 0.001), waist circumference (rS 0.549, P < 0.001), HDL (rS -0.391, P < 0.001), triglycerides (rS 0.375, P < 0.001), Hamaguchi score (rS 0.279, P = 0.007), right lobe of the liver (rS 0.259, P = 0.014), left ventricular mass/body surface area (rS 0.220, P = 0.036).A LSM ≥8 kPa was found in 20.9% of PWH, more commonly in those with EFT above the median >5.6 mm (30.4% vs.11.1%, P = 0.038).LSM significantly correlated with EFT (rS 0.274, P = 0.009), CD4+ cells (rS -0.320, P = 0.003) and nadir of CD4+ cells (rS -0.292, P = 0.007).In a subgroup (n = 53), a homeostasis model assessment of insulin resistance (HOMA-IR) index >2.33 identified increased EFT, [area under the curve (AUC) 0.73, 95% confidence interval (CI) 0.59-0.84, P = 0.001) while an HOMA-IR >3.27 predicted increased LSM (AUC 0.76, 95% CI 0.62-0.87, P = 0.005).Conclusions: PWH with increased EFT have worse metabolic profile and a high proportion of clinically relevant fibrosis at ARFI elastography, despite normal liver function tests.The HOMA-IR index might be used to identify PWH with increased EFT and liver fibrosis
Prima eclissi di sole descritta in volgare
No full textViene presentata la prima descrizione in lingua volgare di un'eclissi, presente nel trattato astronomico di Restoro d'Arezzo. Tale descrizione viene paragonata a quella dell'astronomo Secchi, che descrisse l'eclissi del 1860 per la quale aveva organizzato una spedizione in Andalusia
Mai niente di nuovo sotto il sole del Sud ?
No full textDiscussione - a partire da un articolo degli anni 1870 su ipotesi di colonizzazione del Sudan, e sulla scorta di pubblicazioni recentissime - sulle interpretazioni geopolitiche neocoloniali radicate nella cultura, anche scientifica, occidentale
Le cupole del sole
No full textIl testo introduce la mostra di Marina Bindella tenutasi al Museo laboratorio d'arte contemporanea della Sapienza nel novembre 2015 e affronta la questione della dimensione ambientale nelle opere recenti dell'artist
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