3,295 research outputs found

    The action of neutrino ponderomotive force on supernova dynamics

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    Collective interactions of a beam of neutrinos/antineutrinos traversing a dense magnetized plasma of electrons/positrons, protons and neutrons are studied with particular reference to the case of a Supernova. We find that the ponderomotive force exerted by neutrinos gives, contrary to expectations, a negligible contribution to the revival of the shock for a successful Supernova explosion, although new types of convection and plasma cooling processes induced by the ponderomotive force could be, in principle, relevant for the dynamics itself.Comment: latex, 14 pages; numerical error corrected, conclusions changed; to be published in Mod. Phys. Lett.

    Majorana transformation for differential equations

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    We present a method for reducing the order of ordinary differential equations satisfying a given scaling relation (Majorana scale-invariant equations). We also develop a variant of this method, aimed to reduce the degree of non-linearity of the lower-order equation. Some applications of these methods are carried out and, in particular, we show that second-order Emden-Fowler equations can be transformed into first-order Abel equations. The work presented here is a generalization of a method used by Majorana in order to solve the Thomas-Fermi equation.Comment: RevTex, 8 page

    Majorana solution of the Thomas-Fermi equation

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    We report on an original method, due to Majorana, leading to a semi-analytical series solution of the Thomas-Fermi equation, with appropriate boundary conditions, in terms of only one quadrature. We also deduce a general formula for such a solution which avoids numerical integration, but is expressed in terms of the roots of a given polynomial equation.Comment: RevTex, 5 pages, 1 figur

    A Geometric Picture For Fermion Masses

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    We describe a geometric picture for the pattern of fermion masses of the three generations which is invariant with respect to the renormalization group below the electroweak scale. Moreover, we predict the upper limit for the ratio between the Dirac masses of the ÎŒ\mu and τ\tau neutrinos, mΜΌ/mΜτ<(9.6±0.6)10−3m_{\nu_{\mu}}/ m_{\nu_{\tau}} < (9.6 \pm 0.6) 10^{-3}.Comment: 7 pages LATEX + 1 figur

    Single-tree detection in high-density LiDAR data from UAV-based survey

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    UAV-based LiDAR survey provides very-high-density point clouds, which involve very rich information about forest detailed structure, allowing for detection of individual trees, as well as demanding high computational load. Single-tree detection is of great interest for forest management and ecology purposes, and the task is relatively well solved for forests made of single or largely dominant species, and trees having a very evident pointed shape in the upper part of the canopy (in particular conifers). Most authors proposed methods based totally or partially on search of local maxima in the canopy, which has poor performance for species that have flat or irregular upper canopy, and for mixed forests, especially where taller trees hide smaller ones. Such considerations apply in particular to Mediterranean hardwood forests. In such context, it is imperative to use the whole volume of the point cloud, however keeping computational load tractable. The authors propose the use of a methodology based on modelling the 3D-shape of the tree, which improves performance w.r.t to maxima-based models. A case study, performed on a hazel grove, is provided to document performance improvement on a relatively simple, but significant, case

    Positive or negative voting premium: what happened to private benefits in Italy?

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    A large body of research deals with voting premium as a proxy of private benefit of control. Almost all of them find positive voting premium, in particular in Italy. Therefore appears interesting to ask what is the current status of private benefits of control in Italy in the last decade (2007-2017). Surprisingly, we show three major findings: i) reduction of non-voting share in the Italian scenario; ii) prevalence of negative voting rights premium more than positive ones, thus conflicting with the assumption and the observations by other researchers; iii) limits of the voting premium method. Our aim is that this study, despite its limitations, may encourage further researches focused on the analysis of the improvement and the change in the Italian corporate governance. The article points out that interesting evidence already exists, although still much remains to do in the future

    Interlocking directorates and different power forms: An explorative analysis in the Italian context

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    The purpose of the present paper is twofold. The first is to update the contribution by Drago et al. (2011) about cross-shareholdings and interlocking directorates in Italian listed companies (FTSE MIB) to 31 December 2016 and to reinforce theory of enlarged collusion. The second is to find how interlocking directorates can contribute to understanding the power structure. By using the social network analysis, we map the network structure of interlocking boards and employ centrality measures like degree, eigenvector and betweenness centrality along with the network density and average degree. We interpret eigenvector centrality as a measure of “effective power” of the connections because it can be seen as a weighted sum of not only direct connections but indirect connections, while betweenness centrality as a measure of “potential power” because it is a proxy of the volume of information that passes through the nodes. In this way, we provide a framework for selecting Italian firms with effective and potential power – around whom interactions and processes can be traced and analysed. In addition, we find that the position assumed by the controlling group of the Mediobanca Galaxy is definitely downsized

    Social innovation practices: focus on success factors for crowdfunding

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    This article explores what are the success factor for interaction with platforms of crowdfunding in Italy. Through a Principal Component Analysis we outline three variables and through a multiple regression analysis we demonstrate that the interaction on crowdfunding is positive correlated with socio-economic propensity and cultural level. The analysis has been conducted on a sample of 316 of projects funded in the Crowdfunding platform Produzioni dal Basso, the first platform born in Italy. We draw on SD logic and relationship marketing to underscore the importance of networks of actors and integration to create a co-creation of value. This view emphasizes the social and economic factors that influence, and are influenced by, crowdfundin