1,721,011 research outputs found
Étude par ondes de spin des propriétés magnétiques et électriques des alliages Fe1-xVx et Co2MnSi à température variable
No full textDans ce travail, nous étudions expérimentalement le transport électronique polarisé en spin dans des dispositifs nano-fabriqués à partir de films minces épitaxiaux de C"o" _2MnSi et de F"e" _(1-x) "V" _x. Le premier matériau est un alliage de Heusler n’ayant qu’une bande majoritaire de spin au niveau de Fermi, tandis que le second est un ferromagnétique faible ayant deux bandes de spin au niveau de Fermi. Notre principal outil expérimental est la technique du décalage Doppler des ondes de spin qui nous permet d'estimer le degré de polarisation en spin du courant P =(ρ↓-ρ↑)/(ρ↑+ρ↓) et de séparer les deux canaux de conduction. Pour C"o" _2MnSi, nous avons déterminé un transport électronique polarisé à 100% en spin en accord avec les estimations théoriques, ce qui nous donne un modèle de conduction relativement simple. Dans le cas du Fe, nous avons utilisé une variante dépendante de la température de notre technique expérimentale pour estimer une très haute polarisation en spin du courant (77-86%) dans la plage de température de 10 à 300 K. Cette observation contredit les considérations antérieures, qui, basées sur sa densité globale d'états, prédisent une faible polarisation en spin pour le fer. Enfin, nous avons utilisé nos mesures pour créer un modèle relativement simple afin de comprendre le rôle joué par les surfaces, les phonons ainsi que les magnons dans le transport électronique polarisé en spin dans le Fe.In this work we investigate experimentally the spin-polarized electron transport in nanofabricated devices from C"o" _2MnSi and F"e" _(1-x) "V" _x epitaxial thin films. The first material is a Heusler compound with only a majority spin band crossing the Fermi level, while the second is a weak-ferromagnet with two spin-bands at the Fermi level. Our main experimental tool is the spin wave Doppler shift technique which allows us to estimate the degree of spin-polarization of the current P =(ρ↓-ρ↑)/(ρ↑+ρ↓) and separate the two channels of conduction. For C"o" _2MnSi we determined a 100% spin-polarized electron transport in agreement with theoretical estimations that results in a relatively simple conduction model. In the case of Fe, we have used a temperature dependent variation of our experimental technique to estimate a very high spin-polarization of the current (77-86%) in the temperature range 10-300K. This observation contradicts early considerations, which, based on its global density of states, predicts a week spin polarization for iron. Finally, we used our measurements to create a relatively simple model to understand the role played by surfaces, phonons and magnons in the spin-polarized electron transport in Fe
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
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
Generation of spin-polarized electron currents by ultrafast demagnetization : fundamental processes and applications for THz electronics
No full textSous la tutelle de Christine Boeglin, j'étudie la désaimantation dans un alliage ferrimagnétique de Co61Gd39. En parallèle, je me suis intéressé au profil de concentration de ces couches minces et je les ai reliées aux dynamiques de désaimantation observées. Les alliages de métaux de transition et de terres rares (MT-TR) sont intéressants d'un point de vue fondamental et applicatif. Ce travail est réalisé sur les Très Grandes Infrastructures de Recherche (TGIR) de HZB -BESSY à Berlin et de SOLEIL à Orsay, Paris. Sous la tutelle de Matthieu Bailleul, je fais partie d'une équipe dont l'objectif est d'utiliser un émetteur spintronique pour émettre des ondes THz. Ce type d'émetteur est composé d'une couche générant des électrons chauds à la suite d'une excitation optique, qui est ensuite converti, par les couches métalliques adjacentes, en courants de charge, responsables de l'émission d'un champ électromagnétique dans l'espace libre. Mon travail s'est concentré sur la simulation et la réalisation en salle blanche, d'antennes améliorant cette émission en espace libre.Under the supervision of Christine Boeglin, I study demagnetization in a ferrimagnetic alloy of Co61Gd39. At the same time, I was interested in the concentration profile of these thin layers and I linked them to the observed demagnetization dynamics. Transition metal and rare earth (MT-TR) alloys are interesting from a fundamental and application point of view. This work is carried out on the Very Large Research Infrastructures (TGIR) of HZB - BESSY in Berlin and SOLEIL in Orsay, Paris. Under the supervision of Matthieu Bailleul, I am part of a team whose objective is to use a spintronic transmitter to emit THz waves. This type of emitter is composed of a layer generating hot electrons following optical excitation, which are then converted, by the adjacent metallic layers, into charge currents, responsible for the emission of an electromagnetic field in free space. My work focused on the simulation and creation in a clean room of antennas improving this emission in free space
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe 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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