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Search Results: 1 - 10 of 220991 matches for " Simona C. Minotti "
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Maximum Likelihood Estimation of Gaussian Cluster Weighted Models and Relationships with Mixtures of Regression
Salvatore Ingrassia,Simona C. Minotti
Statistics , 2012,
Abstract: Cluster-weighted modeling (CWM) is a mixture approach for modeling the joint probability of a response variable and a set of explanatory variables. The parameters are estimated by means of the expectation-maximization algorithm according to the maximum likelihood approach. Under Gaussian assumptions, we analyse the complete-data likelihood function of cluster weighted models. Further, under suitable hypotheses we show that the maximization of the likelihood function of Gaussian cluster weighted models leads to the same parameter estimates of finite mixtures of regression and finite mixtures of regression with concomitant variables. In this sense, the latter ones can be considered as nested models of Gaussian cluster weighted models.
Local statistical modeling by cluster-weighted
Salvatore Ingrassia,Simona C. Minotti,Giorgio Vittadini
Statistics , 2009,
Abstract: We investigate statistical properties of Cluster-Weighted Modeling, which is a framework for supervised learning originally developed in order to recreate a digital violin with traditional inputs and realistic sound. The analysis is carried out in comparison with Finite Mixtures of Regression models. Based on some geometrical arguments, we highlight that Cluster-WeightedModeling provides a quite general framework for local statistical modeling. Theoretical results are illustrated on the ground of some numerical simulations.
Model-based clustering via linear cluster-weighted models
Salvatore Ingrassia,Simona C. Minotti,Antonio Punzo
Statistics , 2012, DOI: 10.1016/j.csda.2013.02.012
Abstract: A novel family of twelve mixture models with random covariates, nested in the linear $t$ cluster-weighted model (CWM), is introduced for model-based clustering. The linear $t$ CWM was recently presented as a robust alternative to the better known linear Gaussian CWM. The proposed family of models provides a unified framework that also includes the linear Gaussian CWM as a special case. Maximum likelihood parameter estimation is carried out within the EM framework, and both the BIC and the ICL are used for model selection. A simple and effective hierarchical random initialization is also proposed for the EM algorithm. The novel model-based clustering technique is illustrated in some applications to real data. Finally, a simulation study for evaluating the performance of the BIC and the ICL is presented.
Generalized Linear Gaussian Cluster-Weighted Modeling
Salvatore Ingrassia,Simona C. Minotti,Antonio Punzo,Giorgio Vittadini
Statistics , 2012,
Abstract: Cluster-Weighted Modeling (CWM) is a flexible mixture approach for modeling the joint probability of data coming from a heterogeneous population as a weighted sum of the products of marginal distributions and conditional distributions. In this paper, we introduce a wide family of Cluster Weighted models in which the conditional distributions are assumed to belong to the exponential family with canonical links which will be referred to as Generalized Linear Gaussian Cluster Weighted Models. Moreover, we show that, in a suitable sense, mixtures of generalized linear models can be considered as nested in Generalized Linear Gaussian Cluster Weighted Models. The proposal is illustrated through many numerical studies based on both simulated and real data sets.
A new anti-neutrino detection technique based on positronium tagging with plastic scintillators
G. Consolati,D. Franco,C. Jollet,A. Meregaglia,A. Minotti,S. Perasso,A. Tonazzo
Physics , 2015, DOI: 10.1016/j.nima.2015.06.021
Abstract: The main signature for anti-neutrino detection in reactor and geo-neutrino experiments based on scintillators is provided by the space-time coincidence of positron and neutron produced in the Inverse Beta Decay reaction. Such a signature strongly suppresses backgrounds and allows for measurements performed underground with a relatively high signal-to-background ratio. In an aboveground environment, however, the twofold coincidence technique is not sufficient to efficiently reject the high background rate induced by cosmogenic events. Enhancing the positron-neutron twofold coincidence efficiency has the potential to pave the way future aboveground detectors for reactor monitoring. We propose a new detection scheme based on a threefold coincidence, between the positron ionization, the ortho-positronium (o-Ps) decay, and the neutron capture, in a sandwich detector with alternated layers of plastic scintillator and aerogel powder. We present the results of a set of dedicated measurements on the achievable light yield and on the o-Ps formation and lifetime. The efficiencies for signal detection and background rejection of a preliminary detector design are also discussed.
DUODENOGASTROESOPHAGEAL REFLUX AFTER CHOLECYSTECTOMY
Georgeta Simona Manea,C. Stanciu
Jurnalul de Chirurgie , 2008,
Abstract: The aim of the study was to establish by complementary methods the role of duodenogastroesophageal reflux diagnosed by spectrophotometry in the persistence of postcholecistectomy symptoms correlated with endoscopic lesions of esophageal mucosa. Material and methods: The clinical study was performed on a group of 238 patients divided into two groups: study (170 patients – 71.4%) and control group (68 patients – 28.6%). The study group was formed by patients with classic and laparoscopic cholecistectomy. The study group included 136 females (80%) and 34 males (20%), and the control group included 34 females (50%) and 34 males (50%). In the study group the average age was 54.40 ± 9.932 (SD) years, while in the control group the average age was 51.76 years ± 8.531 (SD). Both control and study group were endoscopically and spectrophotometrically (Bilitec ) examined. Results: The patients in the study group were previously cholecistectomized either by classic (136 cases – 80%) or laparoscopic method (34 cases – 20%);endoscopicaly, 60% cases were type A esophagitis (102 patients), 10% type A and hiatal hernia (17 patients), 10% type B esophagitis (17 patients) and 10% cases Barett esophagus (17 patients). For the control group we had 4.41% cases of hiatal hernia while the rest of 95.59% patients presented normal esophagus. Bilitec showed an mean values of number of refluxes for the study group of 8.000 ± 8.58098 (SD), much higher than the value identified for the control group – 1.7500 ± 0.83532 (SD). The number of long refluxes are much closer between the two groups – study group 2.000 ± 1.73717 (SD), control group 1.4853 ± 0.50350 (SD). Absorbency time > 0.14” is 292.4000 ± 229.941 (SD) for the study group while for the control group the average value is much more low (124.7500 ± 60.51061 (SD)). The values for the esophageal clearance are lower in the study group than in the control group: 77.6900 ± 86.01549 (SD), respectively 147.5250 ± 111.92144 (SD). Conclusions: Cholecistectomy can be included in the category of risk factors for alkaline duodenoesophageal reflux. The endoscopy identified esophagitis lesions, hiatal hernia and Barett esophagus and the Bilitec test allowed the identification of increased alkaline reflux in cholecistectomized patients in comparison with the control group.
LES of a Meso Combustion Chamber with a Detailed Chemistry Model: Comparison between the Flamelet and EDC Models
Angelo Minotti,Enrico Sciubba
Energies , 2010, DOI: 10.3390/en3121943
Abstract: The goal of this paper is to contribute to the design of high-performance mesocombustors, a field currently under rapid development, in particular for propulsion, e.g., for UAVs, and micro/meso-electrical power generators. This study is focused on a cylindrical combustor of 29?cm 3, fuelled by methane and air, which provides 2?kW of thermal power. The device was entirely designed and built at the Sapienza University of Rome and coupled with an ultra-micro turbine. Two 3D LES simulations with detailed chemistry are presented. They differ only for the combustion models, so that a model comparison can be carried out. The calculated maximum temperature inside the chamber, the gas exhaust temperature and the combustion efficiency are compared and discussed. The results, reported at two different physical times, show the effects of the different combustion models, which predict different temperature and species concentration maps, but similar values for the combustion efficiency. Thermal, chemical and kinematic maps show that the Eddy Dissipation Concept allows for a more accurate estimatation of the performance parameters for application to first-order design procedures.
Modello coesivo per l’avanzamento di fratture mediante rilascio nodale di strutture discretizzate con elementi finiti
M. Minotti,P. Salvini
Frattura ed Integrità Strutturale , 2010,
Abstract: La simulazione numerica della propagazione di una frattura in MODO I, viaggiante ad elevata velocità in un acciaio a comportamento duttile è realizzata attraverso un modello coesivo che governa la distribuzione delle forze di rilascio nodale. Come noto, la ricerca di un valore di tensione all’apice non ha alcun senso nel caso elastico; infatti, la tensione può essere valutata solo mediante fattori di campo. Nel caso elastoplastico, incrudimento e softening di origine geometrica o legato al progressivo danneggiamento influiscono decisamente sull’andamento esponenziale del campo tensionale. è possibile comunque individuare un valore di riferimento, di entità finita, mediante estrapolazione delle tensioni elasto-plastiche nella zona di inizio softening della frattura. Tale grandezza può essere presa come fattore di riferimento per il calcolo delle forze di rilascio coesive e quindi dell’energia dissipata. Nel lavoro viene discusso come determinare, dal campo di tensione elasto-plastico locale, il valore che governa la zona coesiva al variare del T-stress
Scalar-tensor theory with enhanced gravitational effects
F. O. Minotti
Physics , 2011,
Abstract: It is shown that a Brans-Dicke scalar-tensor gravitational theory, which also includes Bekenstein's kind of interaction between the Maxwell and scalar fields, has a particular kind of solutions with highly enhanced gravitational effects as compared with General Relativity, prone to laboratory tests.
Scalar-tensor theories and asymmetric resonant cavities
Fernando O. Minotti
Physics , 2013, DOI: 10.1134/S0202289313030080
Abstract: Recently published experimental results indicate the appeareance of unusual forces on asymmetric, electromagnetic resonant cavities. It is argued here that a particular class of scalar-tensor theories of gravity could account for this effect.
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