A genetic algorithm for graphical model selection

ATTI DELLA XXXIX RIUNIONE SCIENTIFICA DELLA SOCIET` ITALIANA DI STATISTICA

Distributed stress fluidisation: insights into the propagation mechanisms of the Abona debris avalanche (Tenerife) through a novel method for indurated deposit sedimentological analysis

Introduction: Volcanic debris avalanches mobilise large volumes and achieve long runouts with high destructive potential. However, the propagation processes that generate them are not currently explained by theoretical or numerical models, which are unable to represent deposit observations. Evaluation of the dynamics represented in deposits is therefore vital for constraining su ch models. The Abona volcanic debris avalanche deposit is located on the southern flank of the island of Tenerife, Spain. The deposit exhibits universal microfracturing and cataclasis. Fluidal features such as fluidal mixing of lithological units and diffuse boundaries, and mixed matrix are observed throughout the deposit. Methods: Field description including sedimentology and facies identification and the evaluation of their distribution have allowed the generation of a new conceptual model for the propagation dynamics of this volcanic debris avalanche, and potentially others with similar properties. The deposit is indurated making the detailed study of its sedimentology difficult, especially clast-size analysis. A novel method utilising structure from motion photogrammetry and photographic sampling was employed. Results: The universal cataclasis of the material and fluidal features suggest that the lack of a major competent material component allowed the mass to fragment and enabled fluidised granular flow behaviour. It is proposed that shear was periodically distributed throughout the body of the avalanche in chaotic temporary shear networks rearranging according to the instantaneous distribution of the mass. Stress and agitation were not temporally or spatially homogenous during propagation. This is also reflected in the unsystematic erosion of the substrate according to the variable basal shear accommodation. Discussion: It is proposed that lithological properties are potentially a determining factor for the propagation mechanisms, stress distribution, and consequently the evolution of a volcanic debris avalanche from the initial collapse to its emplacement. This study highlights the importance of dedicated field examinations of sedimentological, morphological, and structural features for providing constraints for models of volcanic debris avalanche dynamics and the factors dictating them. The novel methodology proposed has the potential of broadening the number of events that can be studied and enhancing the understanding of these complex and hazardous phenomena

Graphical models for skew-normal variates

This paper explores the usefulness of the multivariate skew-normal distribution in the context of graphical models. A slight extension of the family recently discussed by Azzalini & Dalla Valle (1996) and Azzalini & Capitanio (1999) is described, the main motivation being the additional property of closure under conditioning. After considerations of the main probabilistic features, the focus of the paper is on the construction of conditional independence graphs for skew-normal variables. Necessary and sufficient conditions for conditional independence are stated, and the admissible structures of a graph under restriction on univariate marginal distribution are studied. Finally, parameter estimation is considered. It is shown how the factorization of the likelihood function according to a graph can be rearranged in order to obtain a parameter based factorization

Tenofovir treatment in HIV-related lipodystrophy syndrome. Retrospective observational forty-eight weeks follow-up study

Efficacy and safety of morphological and metabolic alterations treatment in HIV related lipodystrophy syndrome have never been evaluated outside clinical trials and progression of lipodystrophy remains uncertain. This is a 48 weeks follow up observational retrospective study over consecutive patients attending the Metabolic Clinic of the University of Modena and Reggio Emilia in whom a biochemical, antropometric with DEXA and psychometric evaluation was available. The aim of this research was to assess efficacy and safety of switching to tenofovir (TDF) in the context of the multidisciplinary interventions offered in the Metabolic Clinic comprehensive of: dietary counseling, physical activities, surgical treatment for facial lipoatrophy or fat hypertrophy and psychological support. In a cohort of 189 people with lipodystrophy, TDF was part of the antiretroviral regimen in 125 individuals (82 males e 43 females). TDF-control group was made of 64 individuals (38 males e 26 females). The two study groups were homogeneous for metabolic, morphologic and psychometric profile at baseline. In the follow up period a significant improvement was observed in TDF+ group with regard of blood glucose, insuline, triglyceride. Non significant change in morphologic alterations evaluated with DEXA was observed in the two study groups. With regards of psychometric evaluations, a striking improvement was observed in aesthetic satisfaction of the face, of the body, of body image and depression. In the cohort, no progressions of HIV disease nor serious adverse events were observed. We conclude that switching to tenofovir in the context of the multidisciplinary interventions offered in the Metabolic Clinic is efficacious and safe in the management of L