1,721,027 research outputs found
Etudes expérimentales des propriétés dispersives de structures photoniques à base de micro-résonateurs pour la réalisation de fonctions optiques
No full textIn this thesis, we present a theoretical and experimental study on the dispersive properties of photonic structures based on microresonators. First, we develop a cavity ringdown based method who fully describe the linear properties of microcavities such as coupling regime and group delay. This homodyne method is successfully applied on a cristalline microdisk (MgF2) and passive and active microspherical resonators to characterize various types of phenomena. In the case of doped microspherical whispering gallery modes resonators, we demonstrate selective amplification filter by combining high spectral selectivity and below threhold laser amplification (gain up to 20 dB at 1.55 μm). In passive high-Q microspheres with high finesse (F > 10^5), we could observe a lift of degeneracy between counter propagating modes. This effect originates from Rayleigh scattering that couples these two modes. This phenomenom is observed in the spectral domain by a splitting of the resonance. In a second step, we study the dispersive properties of coupled-resonator architectures. The coupling of two cavities leads to a splitting of the resonance and a notable decrease in the absorption around the resonance. We experimentally show that it is possible to circumvent limitation imposed by the intrinsic losses of passive resonators using active resonators. This effect can be seen as the classical counter part of Electromagnetically Induced Transparency (EIT). Moreover, we demonstrate that Coupled-Active-Resonator-Induced Transparency is a promising alternative in optical delay line since we can dynamically adjust the delay from a few ns to tens of ns (≈ 90 ns) without any change in the transparency of the system. Furthermore, we propose and experimentally demonstrated tunable cavity-linewidth narrowing based on the strong dispersion induced by the coupling of two resonators. In the case of three resonators, we propose a coupling scheme allowing the Q-factor of a critically coupled resonator to be increased and actively modulated by using two additional coupled resonators. We experimentally validate the principle by means of a model system consisting of Er3+-doped fiber coupled resonators. We successfully show a growth of the Q-factor from 4×10^7 up to 2,5×10^8. These experimental results demonstrate the means of Q-factor tailoring using active artificial photonic media.La caractérisation de résonateurs de facteurs de surtension très élevés (> 10^8) est difficilement réalisée à partir des méthodes expérimentales conventionnelles en régime stationnaire. Nous proposerons une méthode hybride spectrale/temporelle permettant la mesure du facteur de surtension global et la discrimination, de manière univoque, des facteurs Q_0 intrinsèque et Q_e extrinsèque du dispositif. Par cette simple mesure, nous déterminons le régime de couplage et les propriétés dispersives de micro-cavités. Dans un second temps, nous présenterons différentes architectures à base de cavités couplées actives donnant accès un à degré de liberté supplémentaire quant au contrôle de la dispersion. Nous étudierons successivement le phénomène de transparence induite pour la réalisation d'états de lumière lente puis la dispersion induite dans le cas de deux et trois cavités. Dans ce dernier cas, la modulation des pertes intrinsèques mène à un contrôle actif du facteur de qualité de la structure. La démonstration expérimentale de ce principe montre la possibilité d'ingénierie du facteur Q par l'utilisation de structures photoniques artificielles actives
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
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
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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