1,723,593 research outputs found
Le tecniche che derivano dall'analisi in matrici fattoriali di una matrice a tre indici
No full textIn this paper after introducing the FActorial Matrices Analysis (FAMA ) in order to study a three-way matrix (Vichi, 1990), the Author examines techniques already known in literature, that can be derived from FAMA, adding new tools of analysis. Furthermore the Author traduces from FAMA new methodologies to overcome problems connected with some of the known techniques
Clustering microarray data using model-based double K-means
No full textThe microarray technology allows the measurement of expression levels of thousands of genes simultaneously. The dimension and complexity of gene expression data obtained by microarrays create challenging data analysis and management problems ranging from the analysis of images produced by microarray experiments to biological interpretation of results. Therefore, statistical and computational approaches are beginning to assume a substantial position within the molecular biology area. We consider the problem of simultaneously clustering genes and tissue samples (in general conditions) of a microarray data set. This can be useful for revealing groups of genes involved in the same molecular process as well as groups of conditions where this process takes place. The need of finding a subset of genes and tissue samples defining a homogeneous block had led to the application of double clustering techniques on gene expression data. Here, we focus on an extension of standard K-means to simultaneously cluster observations and features of a data matrix, namely double K-means introduced by Vichi (2000). We introduce this model in a probabilistic framework and discuss the advantages of using this approach. We also develop a coordinate ascent algorithm and test its performance via simulation studies and real data set. Finally, we validate the results obtained on the real data set by building resampling confidence intervals for block centroids. © 2012 Copyright Taylor and Francis Group, LLC
Statistical Model-Based Composite Indicators for Tracking Coherent Policy Conclusions
No full textIn the last years, with the data revolution and the use of new technologies, phenomena are frequently described by a huge quantity of information useful for making strategic deci- sions. A priority for policymakers is having simple statistical tools useful to synthesize data. Such tools are represented by composite indicators (CIs). According to the glossary of statistical terms of OECD (The OECD-JRC handbook on practices for developing compos- ite indicators. Paper presented at the OECD Committee on Statistics, 2004), OECD-JRC (Handbook on constructing composite indicators. Methodology and user guide, OECD, Paris, 2008), a CI is formed when manifest (observed) indicators are compiled into a single index, on the basis of an underlying model of the multi-dimensional concept that is being measured, and weights commonly represent the relative importance of each indicator. CIs are increasingly used for bench-marking countries’ performances and the methodologi- cal challenges raise a series of technical issues that, if not adequately addressed, can lead to CIs being misinterpreted or manipulated. Yet doubts are often raised about the robust- ness of the resulting countries’ rankings and about the significance of the associated policy message. In this paper, we propose a model-based approach for the construction of CIs with a hierarchical structure where the CIs (first and second order) are estimated using the Hierarchical Disjoint Non-Negative Factor Analysis (Cavicchia and Vichi in Hierarchical disjoint non-negative factor analysis. Manuscript submitted for publication, 2020) in a LS framework. In order to assess the methodology of construction of a CI, a set of properties is proposed and applied. Some well-known CIs, such as the Human Development Index and the Multidimensional Poverty index, are taken into consideration to show the impor- tance of those properties. Therefore, we include into our proposal the most frequently used approaches in the literature of CIs, and we evaluate the model to assess their performances
Campana "Per vichi fondi" di Genova
No full textAnalisi della poesia di Dino Campana "Per vichi fondi", compresa nel cosiddetto "Quaderno". Sua ripresa e variazione in "Il canto di Genova" di "Il più lungo giorno" e in "Genova" dei "Canti Orfici
The carbonate fraction in carbonatitic Italian lamprophyres
No full textAlkaline and ultramafic lamprophyres represent the majority of pre-Pleistocene alkaline mafic magmatic activity in Italy and have been described from several localities. The age of magmatism ranges from Triassic to Lower Oligocene. Some contain appreciable amounts of carbonate. The primary carbonate of the Italian carbonatitic lamprophyres is mainly Sr- or Mn-rich calcite that occurs mostly as immiscible ocelli or as groundmass. Its textural occurrence, composition, and relationship with co-precipitating silicate phases is taken as evidence of an igneous origin. Low BaO and REE contents in the carbonate are explained by early crystallization of essential mica and subordinate apatite. Whole rock analyses and isotopic data (Rukhlov, A.S., Bell, K., Vichi, G., Stoppa, F., submitted for publication. The heterogeneous deep mantle: the Sr, Pb and Nd isotopic evidence from Early Cretaceous alkaline lamprophyres of Southern Tuscany, Italy. Lithos.) suggest a mantle origin for these rocks and rule out contamination in either high or low pressure regimes. The bulk compositions of the carbonatitic lamprophyres have high HFSE / LILE and LREE / HREE ratios and although the abundances of these elements are generally lower than for carbonatites s.s., they are comparable with the abundances in other ‘carbonate-free’ Italian lamprophyres and Italian carbonatites, suggesting similar mantle sources. Moreover, the age of the Italian lamprophyres, ranging from Middle Triassic to Lower Oligocene, is much greater than the Pleistocene age of Italian carbonatites and indicates that the source remained similar over a long time span
Anomalous dimensions of scalar operators in CFT
No full textWe present a recently developed method to constrain the anomalous dimension of scalar operators in a general Conformal Field Theory (CFT). Using a consistency condition derived from four-point correlation functions it is possible to birid the anomalous dimension of a composite operator phi(2). The result has also consequences on model building.LPT
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