1,721,213 research outputs found
La sorgente "DPP" di radiazione nell'estremo ultravioletto a scarica elettrica in gas rarefatto. Principi fisici, caratterizzazione ed ottimizzazione
Full text linkIn questo rapporto vengono descritti i lavori di installazione, miglioramento e caratterizzazione della sorgente di radiazione nell'estremo ultravioletto a scarica elettrica dell'ENEA (UTAPRAD-SOR). La sorgente, inizialmente progettata e realizzata in collaborazione tra l'ENEA ed il Dipartimento di Fisica dell'Università dell'Aquila, è stata trasferita all'ENEA (Frascati) nell'aprile 2010, priva, però, di molti componenti fondamentali. Per mettere in funzione la sorgente, non disponendo di fondi dedicati, è stato necessario riutilizzare, modificandoli opportunamente, materiali e dispositivi già presenti all'ENEA. Inoltre, per migliorare il funzionamento e le caratteristiche della sorgente, si è provveduto a modificarne radicalmente varie parti, affrontando diverse problematiche fisiche nell'analisi dei principi di funzionamento della sorgente. Attualmente la sorgente è operativa e le sue caratteristiche la rendono idonea per varie applicazioni. Con l'intento di fornire una prima base ad un eventuale futuro studente, in questo rapporto i principi fisici di funzionamento della sorgente e le problematiche affrontate sono stati trattati anche da un punto di vista didattico.In this report we describe the installation, upgrade and characterisation of the ENEA (UTAPRAD-SOR) extremeultraviolet electric discharge source. In April 2010 the source, initially developed in the framework of a collaboration between ENEA and the Physics Department of the University of L'Aquila, has been transferred to ENEA (Frascati), but without many important components. To make the source working, having no dedicated funds, it was necessary to reutilise and properly modify materials and devices already present in ENEA. In order to improve some source features, several critical components of the source have been totally redesigned, analyzing the source working principles and solving various physical problems. Now the source is operating and, due to its characteristics, it is suitable for many applications. With the aim of giving a possible future student a starting point, in this report the source working principles and the scientific problems that we ran into, have been also didactically treated
Complete calibration of a Thomson scattering spectrometer system by rotational Raman scattering in H2
No full textWe describe the complete calibration of a ruby laser-based multipoint Thomson scattering system, performed only by rotational Raman scattering from H2 and the measurement of the absolute Raman cross section of some rotational transitions suitable for such calibrations. The absolute calibration factors (for ne measurements by Thomson scattering) have been measured by observing the Stokes J = 1 → 3 rotational transition at Δv =−587 cm−1(λ = 723.8 nm), with a ≅4.5% accuracy. The relative calibration (for Te measurements) has also been performed by Raman scattering, observing the same line in all the spectral channels. The results agree to within ≅ 10% with those obtained by a tungsten lamp and a lock-in detection technique. From a comparison of the results of the two methods, systematic errors on the measured Te and ne of less than ̃10% (for Te up to 200 eV) are inferred. The absolute cross section of the rotational Raman transitions at Av = −587 cm−1(λ = 723.8 nm), Δv = −354 cm−1(λ = 711..
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
Automatic laser beam alignment for a Thomson scattering system
No full textA system for the automatic alignment of a pulsed ruby laser beam is under development for the Thomson scattering diagnostics of RFX, a large reversed-field pinch machine now under construction. In this experiment the laser will be 11 m from the machine and the beam alignment at the 750×4-mm scattering volume will be actively maintained to within 0.5 mm. The beam direction in space is measured in two reference planes fixed to the collection optics frame by means of two 80-mm2 fast quadrant photodiodes. A double-channel preamplifier is used for each quadrant in order to measure both the 30-ns FWHM ruby pulse and a low-power cw He-Ne beam propagating through the same optical path. Every time the main laser is fired, the relative direction of the two beams is determined so that the position of the He-Ne beam can be used for feedback control of the steering optics between plasma shots
Design of a plasma discharge circuit for particle wakefield acceleration
No full textPlasma wakefield acceleration is the most promising acceleration technique known nowadays, able to provide very high accelerating fields (10-100 GV m -1), enabling acceleration of electrons to GeV energy in few centimetres. However, the quality of the electron bunches accelerated with this technique is still not comparable with that of conventional accelerators; radiofrequency-based accelerators, in fact, are limited in the accelerating field (10-100 MV m-1) requiring therefore kilometric distances to reach the GeV energies, but can provide very bright electron bunches. Combining high brightness electron bunches from conventional accelerators and high accelerating fields reachable with plasmas could be a good compromise allowing to further accelerate high brightness electron bunches coming from LINAC while preserving electron beam quality. Following the idea of plasma wave resonant excitation driven by a train of short bunches, we have started to study the requirements in terms of plasma for SPARC-LAB [1,2]. In particular, here we focus on the ionization process; we show a simplified model to study the evolution of plasma induced by discharge, very useful to design the discharge circuit able to fully ionize the gas and bring the plasma at the needed temperature and density. © 2013 Elsevier B.V
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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