1,721,027 research outputs found
Results and Analysis
No full textIn this chapter the experimental results of this thesis will be shown and the related analysis explained. Four topological insulator crystals (Bi2Se3, Bi2-xCaxSe3, Bi2Se2Te and Bi2Te2Se) have been optically studied by FTIR Spectroscopy, with increasing chemical compensation. They have been measured from 5 to 300K and from subterahertz to visible frequencies. The effect of compensation is clearly observed in the infrared spectra through the suppression of the extrinsic Drude term together with the appearance of strong absorption peaks, that we assign to electronic transitions among localized impurities states. From the far-infrared spectral weight of the most compensated sample (Bi2Te2Se), one can estimate a density of charge carriers on the order of 10(17) cm10(-3) in good agreement with transport data. Those results demonstrate that the low electrodynamics in single crystals of TI, even at the highest degree of compensation presently achieved, is still influenced by three-dimensional charge excitations. Its spectral weight is, indeed, still nearly higher by two orders of magnitude than that expected from the topological surface states, estimated from optical conductivity of films of Bi2Se3 on sapphire substrate. Such films have been measured in the sub-THz and THz frequency region, in order to study their optical conductivity as a function of their thickness. One can observe no appreciable change in the free carriers contribution, while the a phonon intensity strongly decreases with decreasing thickness, demonstrating that the only contribution to the transport is due to surface carriers, not depending on bulk characteristics. The surface metallic state of the thin TI films has been finally studied by patterning the films by a grating, as explained in Chap. 2. This provides the possibility to detect surface plasmonic collective modes, due to the excitation of two dimensional charge density waves along the topological interface of the samples. In the last part of this thesis those plasmons will be analyzed, demonstrating that they have two dimensional nature characteristic of 2DEG
Experimental Technique, Sample Fabrication and Models for Data Analysis
No full textIn this chapter the experimental technique used is described. The Fourier Transform Infrared Spectroscopy allows one to perform reflectivity and transmittance measurements as a function of frequency in awide spectral range, from the far infrared to the ultraviolet. Through Kramers-Kronig transformations it is possible to calculate the linear optical response functions of the material. In this sections the experimental apparatus is also described and the models used to analyze both the reflectivity and transmittance data are discussed. The last part is dedicated to a brief description of the fabrication of plasmonic devises based on TI thin films and to the fitting of the data
Introduction to the Topological Insulators and State of the Art
No full textIn this chapter a brief introduction to the world of topological condensed matter is presented. Firstly, the quantum Hall state in a two dimensional electron gas (2DEG) is introduced. After, the prediction and the subsequent experimental discovery of a topological insulating state of spin-orbit origin is presented. In particular, the so-called strong three dimensional topological insulators (3D TIs) are the object of this thesis. The second part of this chapter focuses on specific 3D TI materials. After their chemical description, their transport and surface properties are reported together with previous optical measurement results
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
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
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