1,721,067 research outputs found
Control of nonlinear recurrences in optical fibers by fine tuning of gain
No full textWe demonstrate experimentally the influence of forcing on the nonlinear stage of modulational instability in standard optical fibers. Weak linear amplification via Raman gain is tuned to characterize the separatrix crossing behavior between successive recurrences
Experimental investigation of the noise-driven thermalization of the Fermi-Pasta-Ulam-Tsingou recurrences process
No full textWe demonstrate the noise-driven thermalization of the Fermi-Pasta-Ulam-Tsingou (FPUT) recurrences in optical fibers. We highlight the progressive recurrences breakup in favor of an irreversible spectral energy equipartition by driving the input noise level
Observation of the symmetry breaking of the Fermi Pasta Ulam recurrence in nonlinear optical fibers
No full textWe provide the first longitudinal characterization in phase and amplitude of the Fermi Pasta Ulam recurrence in optical fibers by means of a heterodyne optical time domain reflectometer. This original setup allows to report the symmetry breaking of the process due to an initial condition change
Non-invasive distributed characterization in phase and intensity of the nonlinear stage of modulation instability
No full textWe report a novel experimental setup to perform distributed characterization in intensity and phase of the nonlinear stage of modulation instability by means of a non-invasive experimental setup: a heterodyne time domain reflectometer
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
Spatio-temporal observation of the Fermi-Pasta-Ulam recurrence in optical fibers
No full textWe report the spatio-temporal observation of the Fermi-Pasta-Ulam recurrence via non-destructive distributed measurements in phase and intensity of main frequency components of the frequency comb
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
Acoustic modes in photonic crystal fibres for distributed optical fibres sensors applications
No full textCe travail de thèse rassemble nos résultats d’étude sur l’utilisation des modes de résonance acoustique pour réaliser des capteurs distribués à base des fibres à cristaux photoniques (Photonic Crystal Fibres : PCF).Tout d’abord, nous avons démontré qu’à l’heure actuelle, il est difficile voire impossible de mesurer en rétrodiffusion les modes acoustiques transverses dans une fibre optique. Ces modes dont la fréquence est inférieure à 2 GHz, ont été mesurés dans une boucle non linéaire sur une PCF, une fibre conventionnelle et une fibre à dispersion décalée. Les différents spectres montrent une dépendance à la structure transverse des fibres.Ensuite, nous avons mis au point un réflectomètre Brillouin (Brillouin Optical Time Domain Reflectometer : BOTDR) permettant de suivre en temps réel le spectre Brillouin le long d’une fibre avec une résolution spatiale de l’ordre d’une dizaine de mètres. Il est particulièrement capable de discriminer différents modes présents dans le spectre Brillouin.La comparaison des spectrogrammes obtenus sur différentes structures transverses de fibres, confirme que l’existence de multipics Brillouin dans les PCF est liée au très petit coeur (dont le diamètre est de l’ordre de la longueur d’onde de mesure) de la fibre.Enfin, toujours dans l’optique de mieux observer le spectre Brillouin distribué, nous avons développé un outil d’analyse Brillouin vectorielle permettant de cartographier avec précision les modes Brillouin hybrides grâce à la complémentarité du spectrogramme de phase. Les mesures réalisées sur une PCF dont le diamètre varie linéairement de 3,5 µm à 2,6 µm montrent un second mode Brillouin dont la fréquence varie à raison de -118,2 MHz/µm.This thesis deals with the results of our study on the use of acoustic resonance modesto achieve distributed sensors based on photonic crystal fibres (Photonic Crystal Fibres :PCF).First, we demonstrated that at present it is difficult to measure backscattered transverseacoustic modes in an optical fibre. These modes whose frequency is below 2 GHzhave been measured in a loop on a nonlinear PCF, a conventional fibre and a dispersionshifted fibre. The different spectra show a dependence on the fibres cross section structure.Then we developed a Brillouin reflectometer (Brillouin Optical Time Domain Reflectometer: BOTDR) to monitor in real time the Brillouin spectrum along a fibre witha spatial resolution of about a dozen meters. It is particularly capable of discriminatingbetween different modes present in the Brillouin spectrum. Comparison of spectrogramsobtained on different transverse structures, confirms that the existence of Brillouin multipeakon PCF is linked to the very small core (with a diameter of about the wavelengthof measurement) of the fibre.Finally, in order to better observe the distributed Brillouin spectrum, we have developeda vector Brillouin optical time domain analyzer for high-order acoustic modes toaccurately map the Brillouin hybrid modes with the complementary phase of the spectrogram.The measurements taken on a PCF whose diameter varies linearly from 3.5 micronsto 2.6 microns show a second Brillouin mode whose frequency varies as -118.2 MHz / um
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