1,721,247 research outputs found
High-nonlinearity dispersion-shifted lead-silicate holey fibers for efficient 1-µm pumped supercontinuum generation
No full textThis paper reports on the recent progress in the design and fabrication of high-nonlinearity lead-silicate holey fibers (HFs). First, the fabrication of a fiber designed to offer close to the maximum possible nonlinearity per unit length in this glass type is described. A value of gamma = 1860 W-1 · km-1 at a wavelength of 1.55 µm is achieved, which is believed to be a record for any fiber at this wavelength. Second, the design and fabrication of a fiber with a slightly reduced nonlinearity but with dispersion-shifted characteristics tailored to enhance broadband supercontinuum (SC) generation when pumped at a wavelength of 1.06 µm - a wavelength readily generated using Yb-doped fiber lasers - are described. SC generation spanning more than 1000 nm is observed for modest pulse energies of ~ 100 pJ using a short length of this fiber. Finally, the results of numerical simulations of the SC process in the proposed fibers are presented, which are in good agreement with the experimental observations and highlight the importance of accurate control of the zero-dispersion wavelength (ZDW) when optimizing such fibers for SC performance
Nonlinear applications of step-index and microstructured soft-glass fibres
No full textThis thesis focuses on the potential of compound-glass, highly nonlinear, small-core fibres for use in nonlinear applications. Both fibres with a conventional step-index design and small-core holey fibres are considered. While the former technology is more mature, the latter represents the ultimate candidate, since it offers the flexibility of combining novel dispersion properties with a very high nonlinearity.With regard to holey fibre designs, small-core, compound-glass holey fibres with different core diameters and designs are considered for two different background materials: a commercially available lead-silicate glass and a bismuth-oxide based glass. Firstly, characterization measurements are performed on the fabricated holey fibres. The measurements reveal the advantages of each glass type and each fibre design, the ultra-high nonlinearity that can be achieved in such fibres and the potential of achieving simultaneously a novel dispersion profile and high nonlinearity. Nonlinear applications are then demonstrated for some of the fibres presented. In particular, the use of a lead-silicate holey fibre, having a dispersion-shifted profile, with a zero-dispersion wavelength lying close to the C-band is demonstrated in cross-phase modulation based wavelength conversion and switching applications in the 1.55 µm window. Both a co-polarized pump and probe scheme and a Kerr-shutter configuration are considered. For the same fibre, the stimulated four-wave mixing process for amplification and wavelength conversion applications in the C-band is thoroughly studied. Numerical simulations and experimental findings are combined to study the fibre performance, demonstrate its applicability to nonlinear wavelength conversion applications and identify future improvement objectives. The suitability of compound-glass holey fibres is also examined for the generation of correlated photons, through spontaneous four-wave mixing, and the generation of a broad supercontinuum by pumping at the convenient in terms of high power laser availability wavelength regions of 1.0 µm and 1.5 µm. The experiments presented in this thesis constitute the first nonlinear applications ever reported for dispersion-tailored, compound-glass holey fibres, clearly revealing their potential in fibre-based nonlinear applications.Nonlinear applications are also demonstrated for a commercially available, fiberised, bismuth-oxide based fibre with a step-index design. Using this fibre, an all-optical regenerator of Return-to-Zero picosecond pulses is realized at repetition rates of 10 and 40 Gb/s. The same fibre is also employed in an all-fiberised pulse compression scheme, which relies on nonlinear pulse propagation in the normal dispersion regime and enables the compression of picosecond pulses down to the femtosecond scale. In both applications, the ultra high nonlinearity of the compound-glass, step-index fibre results in reduced fibre-length and peak power requirements.The thesis concludes by addressing the issues concerning the practicality of compound-glass fibres and proposing potential future directions
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
Oaths, Curses
No full textIn the Hellenistic era, oaths (ὅρκοι hórkoi) and curses (ἀραί araí) – interrelated verbal acts of human communication with the divine – continue to occur in a variety of sources and to perform the usual functions in both private and public life.
Oaths, both public and among individuals, maintain the same structure and language as in the Archaic and Classical periods, the only significant difference being that oaths of loyalty can now be sworn by the name of the ruling king. As regards curses, on the contrary, a significant change in their nature and scope takes place in poetry: Hell. literary ἀραί araí adopt a series of characteristics, including the use of mythological and occasionally historical exempla as a repository of punishments, often organized as a catalogue, a display of erudition, and a humoristic disproportion between the offence and the punishment. Hell. poetic ἀραί araí are revenge curses, as they are uttered in response to a prior offence. Ἀραί, however, can also take the form of conditional curses: the penalties that they threaten will only come into play if the offence is committed. The best example of provisional curses is provided by the so-called ἀραὶ ἐπιτύμβιοι araì epitúmbioi ‘funeral curses’ (Inscriptions of Ancient Greek, 06. Funerary Inscriptions). Attested as early as the sixth-century BCE, but especially common in the Imperial age, they aimed at protecting tombs from maltreatments at the hand of wayfarers
through an explicit prohibition which involves formulaic language (Formulaic Language)
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
A lead silicate holey fibre with gamma=1860 W(-1)km(-1) at 1550 nm
No full textCopyright © 2005 Optical Society of AmericaJulie Y.Y. Leong, Periklis Petropoulos, Symeon Asimakis, Heike Ebendorff-Heidepriem, Roger C. Moore, Ken Frampton, Vittoria Finazzi, Xian Feng, Jonathan H.V. Price, Tanya M. Monro, David J. Richardso
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