1,720,965 research outputs found
Optical/photonic technology for telecommunication satellites
Full text linkLe comunicazioni satellitari (SATCOM) stanno cambiando paradigma: da tecnologia di "nicchia", si stanno muovendo verso l’abilitazione di servizi molto più vicini all'esperienza comune del consumatore, come già avvenuto in passato per l'accesso a Internet e la telefonia mobile. Questo si traduce in nuovi scenari di missione, caratterizzati dalla fornitura di una copertura globale, da maggiori data rate e da una connettività con utenti e sistemi anche diversi da quelli tipici di un'infrastruttura satellitare. In questo senso, la rete satellitare può essere concepita come parte di un "sistema di sistemi" esteso in grado di fornire servizi di comunicazione affidabili, performanti e sicuri, aprendo nuove opportunità di mercato. Questa tendenza è sostenuta dagli sforzi di ricerca delle istituzioni europee e nazionali, dell'università e dell'industria, che danno impulso allo sviluppo di quelle tecnologie considerate abilitanti per la realizzazione di un tale sistema di telecomunicazioni. In questo campo le tecnologie ottiche e fotoniche giocano un ruolo importante. Il presente lavoro di tesi si inserisce in questa linea di ricerca, con l'obiettivo di studiare l'applicabilità delle tecnologie ottico/fotoniche a bordo di payload per SATCOM e di fornirne una dimostrazione di sistema. La prima parte di questa tesi fornisce una panoramica introduttiva sulle comunicazioni satellitari. Dopo una sintesi dei principali servizi e applicazioni, viene descritta la struttura tipica di un sistema SATCOM, le principali architetture di payload e la tassonomia delle orbite. Infine, vengono evidenziati gli scenari attuali e le tendenze future per i sistemi SATCOM, in particolare gli High and Very High Throughput Satellite Systems (HTS e VHTS), le mega-costellazioni in Low Earth Orbit (LEO), le Space Optical Transport Networks (Space OTNs), le costellazioni di micro e nano satelliti, che costituiscono i punti di partenza per un possibile futuro concetto di sistema SATCOM completamente interconnesso. La seconda parte si concentra sulle tecnologie ottiche/fotoniche. In particolare, vengono proposti due approcci per la loro applicazione a un sistema SATCOM: il primo è "a livello di payload", in cui alcuni sottosistemi di payload e le relative funzionalità sono implementati nel dominio ottico anziché in quello microonde/elettrico; il secondo è "a livello di link", in cui vengono sfruttati collegamenti ottici per link space-space e space-ground anziché la classica connettività RF. Vengono poi analizzati i vantaggi della tecnologia microonde-fotonica e della tecnologia di comunicazione ottica nello spazio libero. Infine, vengono descritte le architetture di payload risultanti, ovvero il concetto di payload ibrido microonde/fotonico e il concetto di payload ottico, evidenziandone le differenze e i punti in comune. L'ultima parte di questo documento di tesi si concentra su alcuni dei sottosistemi/funzionalità inclusi nelle suddette architetture di payload, in particolare la conversione di frequenza ibrida microonde/fotonica, la formazione del fascio ottico per payload ibridi microonde/fotonici e la commutazione del circuito ottico in sistemi SATCOM ottici nello spazio libero. Per ciascuna di esse, dopo una breve panoramica sullo stato dell'arte tecnologico, viene fornita una simulazione del sistema e una valutazione delle prestazioni.SATellite COMmunications (SATCOM) are changing their paradigm: moving from being a “niche” technology, they are going to enable services much closer to the common consumer experience, as already happened in the past for Internet access and mobile telephony. This translates into new mission scenarios, characherized by the provision of global coverage, increased datarates and connectivity with users and systems that can be also different from those typical of a satellite infrastructure. In this sense the satellite network can be now conceived as part of an extended “system of systems” providing reliable, performant and secure communication services and opening new market opportunities. This trend is supported by the research efforts of European and national instituions, univerity and industry, which boost the development of those technologies considered enabling for the implementation of such a telecommunication system. In this field optical and photonic technologies play an important role. This thesis work is part of this line of research, with the aim of studying the applicability of optical/photonic technologies on board SATCOM payloads and providing a system demonstration of them. The first part of this thesis document provides an introductory onverview on satellite communications. After a summary of its main services and applications, the typical structure of a SATCOM system is described, as well as the main payloads architectures and the orbits taxonomy. Finally current scenarios and future trends for SATCOM are pointed out, with emphasis on High and Very High Throughput Satellite Systems (HTS and VHTS), mega-constellations in Low Earth Orbit (LEO), Space Optical Transport Networks (Space OTNs), micro and nano satellite constellations, which constitute the starting points of the future concept of a full interconnected SATCOM system. The second part focuses on optical/photonic technologies. In particular two approaches are proposed for their application on a SATCOM system: the first one is “at payload level”, in which some payloads subsystems and the related functionalities are implemented in the optical domain instead of in the microwave/electric one; the second one is “at link level”, where optical space-space and space-ground links are exploited instead of the classical RF connectivity. Then, the benefits of both the microwave-photonic technology and the free space optical communication technology are analyzed. Finally the resulting payload architectures are described, namely the hybrid microwave/photonic payload concept and the optical payload concepts, highlighting their differences and commonalities. The last part of this thesis document focuses on some of the subsystems/functionalities included in the above payload architectures, in particular hybrid microwave/photonic frequency conversion, optical beamforming for hybrid microwave/photonic payloads and optical circuit switching in free space optical SATCOM systems. For each of them, after a short technological state-of-the-art overview, a system simulation and performance evaluation is provided
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
Le attuali strategie terapeutiche nel cancro del polmone producono reali vantaggi sulla sopravvivenza o sono frutto di una migliore selezione?
No full textPROGRESSI IN CHIRURGIA, ANNO VI, VOL. VI, N°3, MAGGIO - GIUGNO 1995, PAG. 72 - 8
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
Vecchie controversie e recenti acquisizioni sul carcinoma della mammella.
No full textPROGRESSI IN CHIRURGIA, ANNO VI, VOL. VI, N°3, MAGGIO - GIUGNO 1995, PAG. 85 - 9
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
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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