1,720,962 research outputs found
Light propagation control with flat plasmonic metasurfaces
No full textNei component ottici convenzionali come lenti, prismi, e lamine d’onda, il controllo del fronte
d’onda è ottenuto attraverso la propagazione della luce nel mezzo. In alterna si possono sfruttare le
discontinuità di fase e polarizzazione associate allo scattering di risonatori ottici per riprodurre lo stesso
effetto. Questo lavoro contiene uno studio delle risposte ottiche di antenne plasmoniche anisotropiche e
una nuova classe di component ottici piatti (“metasuperfici”) basati su array di queste antenne. Vengono
presentati risultati teorici e sperimentali su arrays bidimensionali birifrangenti di antenne ottiche, che
supportano due modi ortogonali che allo la funzione di elementi ottici anisotropici e broadband e che
possono modificare localmente l’ampiezza, la fase e la polarizzazione della luce.
Fenomeni di riflessione e rifrazione anomale sono osservati in metasupercici plasmoniche su di
substrati di silicio con variazioni lineari di fase lungo l’interfaccia. Grazie allo spessore estremamente
sottile rispetto alla lunghezza d’onda degli array di antenna e delle risposte di fase a loro associate, questo
comportamento può essere descritto attraverso una versione generalizzata delle leggi centenarie di
riflessione e rifrazione della luce, derivabili rigorosamente dal Principio di Fermat.
Come dimostrazione della versatilità delle metasupercici, il design e la verifica sperimentale di
un certo numero di component ottici piatti sono proposti: metasuperfici con un gradiente costante che
devia la luce in direzioni arbitrarie; lenti ed axicon piatti che generano fronti d’onda sferici e fasci di
Bessel; metasuperfici con distribuzione di fase a spirale che creano fasci ottici a vortici con un ben
preciso momento angolare orbitale; e metasuperfici con risposta ottica anisotropica che creano fasci di
luce di polarizzazione arbitraria su di un range di lunghezza d’onda ampio.
Infine, si presenta un’analisi dettagliata d’intrappolamento ottico di particelle a basso indice di
rifrazione in cristallo liquido. L’osservazione di un intrappolamento stabile a lungo range, mostra che tale
fenomeno sia regolato da meccanismi completamente diversi da quelli d’intrappolamento convenzionale
in mezzo isotropico. In particolare, il ruolo della non località della riorientazione è rilevato e supportato
da un modello per la riorientazione delle molecole di cristallo liquido in condizioni di forte
focalizzazione
Optical Manipulation in Liquid Crystals: Effects of Tight Focusing on Nonlinear Optical Reorientation
No full text
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Get PDFWe 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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