1,721,089 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
Optical properties of gallium arsenide-based self-assembled quantum dots and quantum dot lasers.
No full textThree-dimensional confinement of carriers eliminates the problem of thermal spreading of carriers observed in higher-dimensional systems. Uniform self-assembled quantum dots (QDs) are obtained using the spontaneous islanding of highly strained III-V semiconductors grown with standard epitaxy. Visible stimulated emission has been obtained with red-emitting AlInAs QDs in AlGaAs barriers. Continuous (CW) threshold current densities below 100A/cm2 have been measured at low temperatures and QD material gain larger than 1.7 x 104 cm-1 demonstrate good material quality. Room temperature lasing has also been observed for higher threshold current densities. For longer wavelengths where the thermionic emission problem is less important, InAs/GaAs lasers can operate at room temperature for current densities below ∼100A/cm2 for wavelengths around 950 nm. The zero-dimensional transitions between confined electrons and holes in artificial atoms allow the observation of state-filling at relatively low level of material excitation. Lasing is observed in the upper QD shells for small gain media, and progress towards the QD ground states for longer cavity lengths. Gain may also be increased by including multiple layers of QDs in the active region. To understand the shell structure of AlInAs/AlGaAs QDs, we present results of interband spectroscopy of single Al0.36In0.64As/Al 0.33Ga0.67As self-assembled QDs. The single dot spectroscopy has been carried out at low temperature as a function of the excitation power and magnetic field up to 8 T. The emission spectra as a function of excitation power show two distinct groups of transitions which we associate with the recombination from ground and excited QD levels with a spacing of ∼70 meV. The application of magnetic field allows to identify the exciton emission as well as the emission from the bi-exciton, and charged exciton complexes with binding energies of ∼5 meV. The binding energies compare favorably with results of calculations. Artificial molecules are studied using coupled QD ensembles and single QD spectroscopy. The coupling between the zero-dimensional states is varied by changing the distance between two layers of stacked InAs/GaAs QDs. Energy level splitting larger than 30 meV of the symmetric and anti-symmetric states of the lowest confined shell are measured and are compared to theory
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
Optical properties of gallium arsenide-based self-assembled quantum dots and quantum dot lasers.
No full textThree-dimensional confinement of carriers eliminates the problem of thermal spreading of carriers observed in higher-dimensional systems. Uniform self-assembled quantum dots (QDs) are obtained using the spontaneous islanding of highly strained III-V semiconductors grown with standard epitaxy. Visible stimulated emission has been obtained with red-emitting AlInAs QDs in AlGaAs barriers. Continuous (CW) threshold current densities below 100A/cm2 have been measured at low temperatures and QD material gain larger than 1.7 x 104 cm-1 demonstrate good material quality. Room temperature lasing has also been observed for higher threshold current densities. For longer wavelengths where the thermionic emission problem is less important, InAs/GaAs lasers can operate at room temperature for current densities below ∼100A/cm2 for wavelengths around 950 nm. The zero-dimensional transitions between confined electrons and holes in artificial atoms allow the observation of state-filling at relatively low level of material excitation. Lasing is observed in the upper QD shells for small gain media, and progress towards the QD ground states for longer cavity lengths. Gain may also be increased by including multiple layers of QDs in the active region. To understand the shell structure of AlInAs/AlGaAs QDs, we present results of interband spectroscopy of single Al0.36In0.64As/Al 0.33Ga0.67As self-assembled QDs. The single dot spectroscopy has been carried out at low temperature as a function of the excitation power and magnetic field up to 8 T. The emission spectra as a function of excitation power show two distinct groups of transitions which we associate with the recombination from ground and excited QD levels with a spacing of ∼70 meV. The application of magnetic field allows to identify the exciton emission as well as the emission from the bi-exciton, and charged exciton complexes with binding energies of ∼5 meV. The binding energies compare favorably with results of calculations. Artificial molecules are studied using coupled QD ensembles and single QD spectroscopy. The coupling between the zero-dimensional states is varied by changing the distance between two layers of stacked InAs/GaAs QDs. Energy level splitting larger than 30 meV of the symmetric and anti-symmetric states of the lowest confined shell are measured and are compared to theory
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
Conception d'un montage de caractérisation spécialisé dans l'étude de convertisseurs de puissance laser
Get PDFLe développement de dispositifs photovoltaïques est un processus complexe qui nécessite une compréhension en profondeur de leur fonctionnement et des particularités des matériaux semiconducteurs. Une multitude de méthodes sont communément employées pour déterminer les caractéristiques d'un dispositif et pour étudier le comportement d'une cellule photovoltaïque en opération. Ces techniques ont d'abord été conçues en fonction des attributs spécifiques des cellules solaires, c'est-à-dire que les conditions expérimentales simulent une exposition à la lumière du Soleil. Par contre, certains types de dispositifs photovoltaïques sont conçus pour convertir l'énergie provenant d'une source laser, or les méthodes de caractérisation conventionnelles ne sont pas adéquates pour ce genre de cellules. Ce projet porte donc sur l'adaptation d'un montage de caractérisation dans le but d'étudier les attributs de convertisseur de puissance laser avec des conditions expérimentales plus pertinentes à leur mode de fonctionnement. La fonction principale d'un tel montage consiste à effectuer une mesure du courant généré par une cellule illuminée tout en variant la tension appliquée aux bornes. Une analyse des résultats obtenus peut ensuite être effectuée pour déterminer les caractéristiques du matériau semiconducteur, comparer les performances expérimentales à celles théoriques et finalement pour identifier des défauts dans le dispositif.
Le premier objectif de ce projet consistait à installer une source de puissance laser à longueur d'onde variable. Une calibration de la puissance de sortie du laser en fonction de la longueur d'onde d'émission a été effectuée et des régimes de puissances ont été identifiés. Les fluctuations étaient trop importantes pour pouvoir prédire avec confiance la puissance qui atteignait l'échantillon. Pour remédier à la situation, un wattmètre a été placé devant la sortie du laser où une portion excédentaire du faisceau était déviée afin d'évaluer la puissance du laser durant une mesure. La la puissance à la sortie du système était contrôlée par un polariseur linéaire sur le parcours optique. Une étape de calibration a été faite pour vérifier que le rapport entre la puissance de sortie et celle éjectée du système est stable. Un rapport expérimental a été établi afin de pouvoir déduire la puissance de sortie du laser à partir de la mesure de puissance effectuée par le wattmètre. Suite à la découverte d'une diminution graduelle de la puissance de sortie au fil du temps, une maintenance du système qui consiste à déshumidifier la cavité du laser et à réaligner les miroirs dans le réseau optique a été effectuée. Une analyse de résultats obtenus à partir du montage a été réalisée afin d'exposer les nouvelles capacités du système. Le deuxième objectif principal du projet consistait à ajouter un montage de caractérisation I-V en fonction de l'angle d'incidence du faisceau laser. Tout comme pour une cellule solaire, l'angle d'incidence de la lumière peut avoir un impact significatif sur l'efficacité du système. Un moteur pas-à-pas contrôlé par une carte Arduino a été installé de manière à faire pivoter un échantillon durant une mesure. Des supports fabriqués par impression 3D ont été utilisés pour attacher les différents formats de dispositifs au tronc du moteur et la fibre optique acheminant la lumière a été positionnée au dessus de l'échantillon. Un exemple d'analyse de résultats obtenus à partir du montage a ensuite été réalisé pour démontrer les nouvelles fonctionnalités du système. Finalement, un programme d'acquisition Labview a été développé afin de contrôler automatiquement chaque composante du montage. L'optimisation des paramètres de mesure fait en sorte que les séances de caractérisation ont été plus rapides et que les risques associés à l'utilisation de sources lasers à haute puissance ont été réduits
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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