1,720,984 research outputs found
Nonequilibrium electron spin relaxation in n-type doped GaAs sample
No full textNon-equilibrium electron spin relaxation in a n-type doped GaAs bulk semiconductor is investigated. We use a semiclassical Monte Carlo approach by considering multivalley spin dynamics of drifting electrons. Spin relaxation is considered through the D'yakonov-Perel mechanism, which is the dominant process in III-V semiconductors. An analytical expression for the inhomogeneous broadening of spin precession vector is derived by taking into account the effect of the electric field and the doping density. The inclusion of electron-electron scattering has the effect of increasing both the spin lifetime and the depolarization length. In particular, we find a non-monotonic trend with the maximum of both the spin lifetime and the depolarization length, as a function of the lattice temperature. This peculiar behavior, which is due to the nonlinear spin-lattice interaction through the phononic thermal bath, is akin to the noise-enhanced stability phenomenon. Moreover, for lattice temperatures up to 77 K the electron spin lifetime slightly increases with the doping density, while the spin depolarization length shows a decreasing behaviour. For electic field amplitudes higher than the threshold field (Gunn field), the spin lifetime increases with the lattice temperature. Our numerical findings are validated by a good agreement with the available experimental results
The amazing graphene: an educational bridge connecting different Physics concepts
Full text linkThe purpose of this work is to present a learning workshop covering various
physics concepts aimed at strengthening physics/engineering student understanding
about the remarkable properties of two dimensional materials, graphene
in particular. At the basis of this learning experience is the idea of
blending and interconnecting separate pieces of knowledge already acquired
by undergraduates in different courses and to help them visualize and link the
concepts lying beyond separate chunks of information or equations. Graphene
represents an appropriate unifying framework to achieve this task in view of its
monatomic structure and various exotic processes peculiar to this and some
other two dimensional crystals. We first discuss essential elements of group
theory and their application to the symmetry properties of graphene with the
aim of presenting to physics/electronic engineering undergraduates that in a
system characterized by symmetry properties such as a crystal, the acquisition
of the solutions of the Schrödinger equation is simpler and easier to visualize
than when these properties are ignored. We have then selected and discussed
some remarkable properties of graphene: the linear electron energy-momentum
dispersion relation in proximity of some edge points of the Brillouin zone;
the consequential massless Dirac behaviour of the electrons; their tunnelling
behaviour and the related Klein paradox; the chiral behaviour of electrons and
holes; the fractional quantum Hall effect in massless particles; and the
quantum behaviour of correlated quasiparticles observable at macroscopic
level. These arguments are presented in a context covering related pieces of
knowledge about classical, quantum and relativistic mechanics. Finally, we
mention current applications and possible future ones with the aim of providing
students with an expertise that could be useful for further work experiences and scientific investigations regarding new materials, having farreaching
implications in various fields such as basic physics, materials science
and engineering applications
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
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