1,720,996 research outputs found
Study on electron emission by a spherical object: dynamics of trapped particles
Full text linkIn this paper, the dynamics of electrons emitted by a spherical object when the total charge of the system is constant is studied in detail. In particular, the condition for which the total electron charge presents damped oscillations is deduced rigorously by considering a perturbation with respect to the steady-state solution. The results obtained can be of utility in simulating the expansion of a spherical plasma by separating the ion and electron time scales
Il modello Sulcis
Full text linkLa notorietà dei vini prodotti con Carignano e soprattutto di quelli ottenuti da viti franche di piede sta progressivamente aumentando.
La maggior parte dei vigneti presenti in questo territorio è molto vecchia, inoltre, si tratta di viti franche di piede coltivate su terreno sabbioso che non vengono danneggiate dalla fillossera. Queste particolarità sono state oggetto di approfondimento comunicando ai consumatori le peculiarità del “Piede franco”. La Vitis vinifera non innestata è assai tollerante alla siccità, inoltre, i terreni sabbiosi, poveri e drenati inducono un vigore limitato alle piante e l’elevata insolazione favorisce l’accumulo degli zuccheri, dei composti secondari e i fenomeni di polimerizzazione dei tannini che permettono di ottenere vini di Carignano con elevata morbidezza e di elevata qualità potenziale. L’analisi sensoriale, condotta secondo il metodo utilizzato da Scalabrelli, sugli acini provenienti da un vigneto franco di piede di circa 150 anni, ha rivelato una buona maturazione fenolica del vinacciolo e soprattutto della polpa.
L’ambiente in cui si pratica la viticoltura è, pertanto, idoneo ad una viticoltura eco-sostenibile, così come ormai si sta programmando in ogni parte del mondo. Infatti, la parola chiave, sostenibilità non è solo il cavallo di battaglia dei tecnici, ma anche di chi fa cultura degli amministratori e dei politici. Di certo nel nostro caso l’importante non è programmarla ma poterla esercitare. La peculiarità di questi vigneti sta non solo nelle caratteristiche specifiche del sito: clima ventilato e mitigato dalla vicinanza del mare, terreno sabbioso, frangiventi, piede franco, allevamento ad alberello, piccola dimensione della proprietà, ma anche nell’abilità di allevare le viti che è stata tramandata nel tempo costituendo un motivo importante nell’attuazione di una viticoltura durevole. La notevole longevità delle viti, la quale si spiega solo in funzione dell’adozione di una tecnica di “potatura conservativa”, che affonda le radici di un fare sapiente acquisito con l’esperienza, costituendo una combinazione efficace nell’allevamento della vite ad alberello senza sostegni, idoneo a mantenere la vite in condizioni di stress moderato durante il periodo estivo
Time-average and ergodic methods for the dynamics of electron plasmas
Full text linkThe paper deals with the dynamics of electrons confined by a twodimensional
electrostatic field and by a constant magnetic field. The electrons undergo
collisions with neutral atoms, with frequency much smaller with respect to the
characteristic frequencies of the motion. In this situation, suitable time averages of
the trajectories can be introduced in order to simplify the analysis of the problem.
Two different approaches are described: (1) the time average of the trajectories and
(2) the use of a suitable ergodic distribution. Results obtained with the two methods
are presented and discussed
Spectral theory of weighted hypergraphs via tensors
No full textOne way to study a hypergraph is to attach to it a tensor. Tensors are a generalization of matrices, and they are an efficient way to encode information in a compact form. In this paper, we study how properties of weighted hypergraphs are reflected on eigenvalues and eigenvectors of their associated tensors. We also show how to efficiently compute eigenvalues with some techniques from numerical algebraic geometry
Random Geometric Complexes and Graphs on Riemannian Manifolds in the Thermodynamic Limit
Full text linkWe investigate some topological properties of random geometric complexes and random geometric graphs on Riemannian manifolds in the thermodynamic limit. In particular, for random geometric complexes we prove that the normalized counting measure of connected components, counted according to isotopy type, converges in probability to a deterministic measure. More generally, we also prove similar convergence results for the counting measure of types of components of each k-skeleton of a random geometric complex. As a consequence, in the case of the 1-skeleton (i.e., for random geometric graphs) we show that the empirical spectral measure associated to the normalized Laplace operator converges to a deterministic measure
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Ergodic model for the dynamics of a pure electron plasma
No full textIn a Penning trap in which Larmor, bouncing and dio- cotron frequencies are of the same order of magnitude, the trajectory of single electrons is intractable analytically. However, perturbations to the ideal electrostatic potential lead to a sort of ergodic density for the electrons. Accord- ing to this hypothesis, a model for the dynamics of the electron plasma is presented, in which the electron-neutral collisions are taken into account by using a Monte Carlo approach
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