1,721,100 research outputs found
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
A study of light dynamics and measurements of the nonlinear optical characteristics of carbon disulphide
No full textNous présentons une étude de la dynamique de la lumière et des mesures des caractéristiques non-linéaires optiques dans le disulfure de carbone.Dans la première partie, nous calculons dans le cadre d’un modèle classique des expressions des susceptibilités non-linéaires jusqu’au cinquième ordre, en tenant compte des corrections de champ local. Nous formulons différentes hypothèses que nous confirmons ou infirmons par la mesure des indices d’absorption et de réfraction non-linéaires. Celles-ci sont obtenues en combinant deux méthodes de caractérisation des non-linéarités au sein d’un système 4fd’imagerie. L’analyse des données expérimentales utilise une méthode nouvellement développée, qui consiste à inverser numériquement, par la méthode de Newton, les solutions analytiques des équations différentielles qui décrivent l’évolution du faisceau.Dans la deuxième partie, nous observons la filamentation d’un faisceau laser à la longueur d’onde de 532 nm et en régime picoseconde. Puis nous procédons à la mesure de l’indice de réfraction non-linéaire effectif du troisième ordre n2,eff en fonction de l’intensité incidente. Par un ajustement de la courbe de saturation de l’effet Kerr,nous développons un nouveau modèle. La résolution numérique de celui-ci reproduit la filamentation observée.La dernière partie est consacrée à l’étude de la dynamique des solitons dissipatifs au sein de milieux à gains et pertes non-linéaires. La résolution numérique de l’équation complexe de Ginzburg-Landau cubique-quintique est réalisée suivant différentes configurations :soliton fondamental, dipôle, quadrupôle,vortex carré et rhombique.We present a study of light dynamics and measurements of the nonlinear optical characteristics of carbon disulphide. In the first part, we calculate using the classical model, the nonlinear susceptibilities up to the fifth order taking into account local field corrections. We express different assumptions that we confirm or refute by measuring the nonlinear absorption coefficient and the nonlinear refractive index. The measurements are performed by means of two nonlinear characterization methods combined with an imaging 4f system. We analyse the experimental data using a newly developed method which numerically inverts the analytical solutions of the differential equations which describe the evolution of the beam, using Newton’s method. In the second part, we observe light filamentation at wavelength 532 nm, in the picoseconds regime. Then we measure the effective third order nonlinear refractive index n2,eff versus the incident intensity. By fitting the curve of the Kerr effect saturation, we develop a new model. Numerically solving this model, allows us to reproducethe experimentally observed filamentation. The last part is dedicated to the study of dissipative solitons dynamics. The complex Ginzburg-Landau equation with cubic-quintic nonlineraties is numerically solved in various configurations : soliton fundamental dipole, quadrupole, vortex and square rhombic
Visible, UV and IR nonlinear optical characterization in the picosecond regime. : case of the most commonly used solvents, lithium niobate and graphene quantum dots.
No full textCette étude concerne la caractérisation optique non linéaire (NL) principalement d’ordre 3 dans le visible, l’UV et l’IR en régime picoseconde de différents matériaux tels que certains solvants, le niobate de lithium et les nano-feuilles de graphène. Nous présentons d’abord les expressions des susceptibilités NL. Nous décrivons ensuite la technique de caractérisation Z-scan et ses variantes. Nous présentons une nouvelle méthode qui combine les avantages de Z-scan avec ceux de la microscopie en champ sombre. Nous montrons que cette technique d’imagerie, nommée DFZscan (Dark Field Z-scan), peut mesurer les coefficients de réfraction NL en présence d'une forte absorption NL. Les résultats expérimentaux montrent une importante amélioration de la sensibilité. Finalement, nous comparons les réponses NL des solvants les plus utilisés, dont l’eau qui possède la réfraction NL la plus faible. Ce liquide est utilisé pour caractériser la réponse NL d’une suspension de points quantiques de graphène. Grâce à un modèle simple, nous estimons l'indice de réfraction et d’absorption NL d'une nanofeuille de graphène monocouche. Nous étudions également les non linéarités d’ordres supérieurs dans les matériaux liquides (toluène) et solides (LiNbO3) en vue d’applications potentielles pour la génération de la deuxième harmonique et des modulateurs de guides d'ondes. Ces coefficients peuvent intéresser une grande communauté de chercheurs dans des domaines aussi variés que la filamentation, les solitons, le traitement tout optique du signal et les réseaux de télécommunications.This study concerns the nonlinear (NL) optical characterization mainly of order 3 in the visible, UV and IR in the picosecond regime of different materials such as solvents, lithium niobate and graphene nanosheets. We first present the expressions of NL susceptibilities. We then describe the Z-scan characterization technique and its variants. We present a new method that combines the advantages of Z-scan with those of dark field microscopy. We show that this imaging technique, called DFZ-scan (Dark Field Z-scan), can measure NL refractive coefficients in the presence of high NL absorption. The experimental results show a significant improvement in the sensitivity. Finally, we compare the NL responses of the most commonly used solvents, including water with the lowest NL refraction. This liquid is used to characterize the NL response of a suspension of graphene quantum dots. Using a simple model, we estimate the refractive index and absorption index NL of a single-layer graphene nanosheet. We also studied higher order non-linearities in liquid (toluene) and solid (LiNbO3) materials for potential applications in second harmonic generation and waveguide modulators. These coefficients can be of interest to a large community of researchers in fields as diverse as filamentation, soliton, all-optical signal processing and telecommunications networks
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
Development of optical phase shift measurement methods : applications to non-linearities induced by the Kerr effect in certain organic molecules
No full textNotre étude concerne la mesure du déphasage optique non linéaire (NL) d’ordre trois. Deux catégories de procédés seront abordées : i) la technique interférométrique à décalage de phase qui permet la caractérisation de la phase avec une bonne résolution spatiale, ce qui est crucial pour un faisceau focalisé dans le milieu non linéaire. Cette technique utilise le critère des moindres carrés associé à plusieurs interférogrammes. Mise en œuvre à l'aide d'un modulateur spatial de lumière, elle fournit un calibrage pratique pour chaque déphasage considéré. La fiabilité de la méthode proposée est vérifiée par comparaison directe avec la méthode de transformation de Fourier ; ii) les méthodes innovantes de type Z-scan combinées avec un montage imageur. Elles seront ici appliquées aux mesures des coefficients NL d’ordre trois et d’ordres supérieurs. Nous montrerons que la flexibilité d’emploi d'une caméra CCD permet un meilleur pointage et suivi en temps réel du faisceau. Enfin nous nous intéresserons au montage Dark-field Z-scan bénéficiant des avantages de la microscopie à champ sombre à fort contraste. Ces améliorations ouvrent potentiellement un nouveau champ d’exploration microscopique pour l’investigation et la cartographie des effets non linéaires.Our study concerns the measurement of the nonlinear (NL) optical phase shift of order three. Two categories of methods will be addressed: i) the phaseshift interferometric technique that allows phase characterization with good spatial resolution, which is crucial for a focused beam in the non-linear medium. This technique uses the least squares criterion associated with several interferograms. Implemented using a spatial light modulator, it provides a practical calibration for each phase shift considered. The reliability of the proposed method is verified by direct comparison with the Fourier transformation method; ii) innovative Z-scan methods combined with an imager assembly. They will be applied here to measurements of the NL coefficients of order three and higher. We will show that the flexibility of using a CCD camera allows for better pointing and real-time tracking of the beam. Finally, we will focus on the Dark-field Z-scan setup, which benefits from the advantages of high contrast dark field microscopy. These improvements potentially open up a new field of microscopic exploration for the investigation and mapping of non-linear effects
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
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