1,721,019 research outputs found
Electronic structure of tin oxides
No full textStannic oxide SnO2 is a technologically important material which is frequently obtained by the oxidation of SnO. The tin oxides both have a tetragonal structure which differ essentially by the insertion of an oxygen plane between two tin planes in the layered SnO crystal. In order to well understand this structural evolution, it is crucial to have a precise description of the atomic and electronic structure of the two oxides. Preliminary results of calculations performed within Density Functional Theory in the Local Density Approximation (DFT-LDA) have already shown the relation existing between the electronic and geometric configurations of the two oxides. The gap calculated for SnO2 was in good agreement with the experimental value, but the calculations did not reproduce with a very good accuracy the experimental structure of SnO. We present ab-initio (DFT-LDA) study of the electronic structure of SnO, in comparison with SnO2. The charge density distribution of each oxide is analyzed with a special emphasis on low-charge-density contributions. Particular problems in the calculation of the equilibrium structure due to the pseudopotential of tin are put into evidence. We discuss the origin of these problems, and a possible solution
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
Ab initio pseudopotential calculation of the equilibrium structure of tin monoxide
Full text linkWe present an ab initio pseudopotential calculation of the structural properties of stannous oxide SnO. We discuss the delicate balance of different contributions to the cohesion of this material, and compare the monoxide to the dioxide SnO2. We point out how different choices concerning the pseudopotential of tin may dramatically influence the resulting equilibrium structure of SnO, and show that the physically most appropriate choice leads to excellent agreement with experiment
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
Silicon−Germanium Nanowires: Chemistry and Physics in Play, from Basic Principles to Advanced Applications
No full textCONTENTS
1. Introduction 1371
2. Growth Techniques, Morphology, and Structural
Properties 1373
2.1. Alloyed Nanowires 1373
2.2. Axial Heterostructures 1375
2.3. Radial Heterostructures 1377
3. Chemical and Physical Properties 1379
3.1. Electronic Properties 1379
3.1.1. Modulation of the Electronic Properties
by Composition Control 1379
3.1.2. Interfaces at Work: Strain, Band-Offset,
and Carrier Gases 1381
3.1.3. Doped Nanowires 1384
3.2. Thermal and Thermoelectric Properties 1385
4. Theoretical Modeling 1389
4.1. Electronic Structure 1390
4.1.1. Quantum Confinement Effect and Band
Offset 1391
4.1.2. Size Effects 1393
4.1.3. Alloying and Interface Effects 1394
4.1.4. Strain Effects 1395
4.1.5. Addition of Impurities 1395
4.1.6. Electronic Transport 1396
4.1.7. Optical Properties 1397
4.2. Phonons and Thermal Conductivity 1398
4.2.1. Breakdown of Fourier’s Law at Nanoscale 1398
4.2.2. Numerical Simulations of Thermal Properties
1398
5. Devices and Applications 1402
5.1. High-Performance Nanoelectronic Components
1403
5.1.1. Si1−xGex Alloy Nanowire Transistor 1403
5.1.2. Si-Shell Ge-Core Nanowire Transistor 1404
5.2. From Quantum Transport to Superconductivity:
SiGe Nanowires As Platforms for
Fundamental Physics Studies 1405
6. Conclusions and Perspectives 1405
Author Information 1406
Corresponding Authors 1406
Notes 1406
Biographies 1407
Acknowledgments 1408
References 140
Ab initio optical properties of BN in the cubic and in the layered hexagonal phase
No full textWe present our ab initio calculation of linear optical properties in cubic (c-BN) and layered hexagonal BN (h-BN). Our results show a reasonable agreement with existent theoretical results and with measured data for the imaginary part of the dielectric function in the case of h-BN, while for c-BN discrepancies arise between theory and experiment. We discuss the possible reasons of this mismatch. (C) 2001 Elsevier Science B.V. All rights reserved
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
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