1,720,990 research outputs found
Structure, electronic properties and formation mechanisms of Hydrogen-Nitrogen complexes in GaP(y)N(1-y) alloys
No full textNitrogen passivation by atomic hydrogen in GaAsyN1-y and InxGa1-xAsyN1-y alloys
No full textPrevious theoretical studies on N-H complexes in GaAsN have been extended here to new di-hydrogen complex configurations and to N-H complexes in the In0.25Ga0.75As0.97N0.03 alloy. Moreover, a deeper analysis has been performed on the structure, formation energies, chemical bonding and electronic properties of old and new N-H complexes in the above alloys. On the ground of the achieved results, the existence of a novel di-hydrogen complex is predicted that is characterized by a C-2v symmetry and peculiar vibrational properties. Complexes with this symmetry are not stable in N-free GaAs. Further, we propose a sound model for the N passivation founded on the characteristics of the electronic states and the local atomic relaxations induced by the N-H complexes. This model explains why the N passivation is not achieved in the case of monohydrogen complexes and realized through the formation of the N-H-2(*) dihydrogen complexes. Finally, it is suggested that different N-H complexes (and different vibrational spectra) should be observed in hydrogenated p-type and n-type N-containing alloys
Theory of hydrogen complexes in Mn(x)Ga(1-x)As dilute magnetic semiconductors
No full textAtomic hydrogen diffuses in semiconductor lattices and binds to impurities by forming complexes that can lead to a full neutralization of the impurity effects. In the present paper, the structural, vibrational, electronic and magnetic properties of complexes formed by H in the Mn xGa1-xAs (x=0.03) dilute magnetic semiconductor have been investigated by using first-principles DFT-LSD and LDA+U theoretical methods. The results account for recent experimental findings showing a H passivation of the electronic and magnetic properties of Mn in GaAs. Moreover, they show that electron correlation has crucial effects on the properties of H-Mn complexes
Short hydrogen bonds at the water/TiO2 (anatase) interface
No full textThe nature of peculiar, short H bonds formed by water molecules in contact with the (101) anatase surface and their effects on the structural and vibrational properties of the first water layers adsorbed on the same surface have been investigated by performing density functional theory (DFT) total energy calculations and ab initio molecular dynamics (AIMD) simulations at different temperatures. Present results show that these short H bonds originate from a water/anatase interface effect related to an electronic charge transfer from surface Ti atoms to surface O atoms, mediated by water molecules. Further, AIMD simulations per-formed at low temperature indicate that such short H bonds are at the ground of both the atomic arrangements of the water layers and the peculiar features appearing in the corresponding vibrational spectra. The same interface effect significantly influences also the atomic arrangements and the vibrational properties of intermediates of the O-2 photoreduction reaction, which turn out to be involved in similar charge transfer processes as well as in the formation of short H bonds. AIMD simulations show that these short H bonds are still present at room temperature and give estimates of the vibrational frequencies of the same intermediates, which are in a quite good agreement with the experimental findings. Such an agreement supports the unifying theoretical picture proposed here for water molecules and O-2 photoreduction intermediates in contact with the anatase surface
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
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
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