1,720,974 research outputs found
Electrically controlled spin dynamics in disordered semiconductors
Get PDFThe spin of electrons in a semiconductor environment couples not only to magnetic fields, but also to the orbital motion of the electron. As a consequence, transport in semiconductors includes a class of phenomena in which electrically induced charge motion influences the electron spin. The intricate interplay of spin and charge makes this type of effects a diverse research field of fundamental interest, but is also of practical relevance: Spin-orbit interaction (SOI) provides a mechanism to control the spin with electric fields. Being available in tailored materials, that are routinely used in microelectronics, SOI has therefore attracted intense interest for its potential in applications to use the electron spin alternatively to the charge in new types of electronic devices. In this thesis we investigate the interplay of spin and charge transport in disordered electron systems, where random impurities not only determine the electrical resistance but also the spin dynamics through spin-orbit interaction. A focus of this work is electric-dipole-induced spin resonance (EDSR), a versatile scheme of spin control using electric fields. Similar to standard paramagnetic resonance where a combination of static and ac magnetic fields drive spin rotations, in EDSR ac electric fields couple resonantly to the spin. Appropriately chosen pulses of these electric fields, which can be generated easier on-chip than ac magnetic fields, allow to achieve arbitrary spin rotations. In a diagrammatic analysis we find that the presence of disorder broadens the line-shape of EDSR and determines the maximal achievable polarization. We identify random internal magnetic fields as the origin of this line-broadening, which limits the efficiency of EDSR, and show that these limitations can be overcome in an optimal geometry where the internal fields are suppressed by the interference of different spin-orbit mechanisms. This leads to a substantial enhancement of the spin polarization at resonance. We moreover link these findings to spin currents giving rise to the spin-Hall effect. We interpret these spin currents in terms of spin polarization components. The behavior of the spin depends sensitively on whether the orbital motion is diffusive or phase coherent. Indeed, qualitatively different – mesoscopic – effects occur in the spin when electrons flow through phase-coherent systems. Whereas in charge transport such mesoscopic effects are well known, for the spin they have attracted interest only more recently in the context of spintronics. We find that the spin polarization, that arises due to dc transport and SOI, shows large mesoscopic fluctuations that exceed the polarization in incoherent samples with self-averaging. Since this average polarization has been successfully measured we expect this mesoscopic fluctuations to be within experimental reach as well
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
Mesoscopic fluctuations in the spin-electric susceptibility due to Rashba spin-orbit interaction
No full textWe investigate mesoscopic fluctuations in the spin polarization generated by a static electric field and by Rashba spin-orbit interaction in a disordered 2D electron gas. In a diagrammatic approach we find that the out-of-plane polarization-while being zero for self-averaging systems-exhibits large sample-to-sample fluctuations which are shown to be well within experimental reach. We evaluate the disorder-averaged variance of the susceptibility and find its dependence on magnetic field, spin-orbit interaction, dephasing, and chemical potential difference
Resonant spin polarization and spin current in a two-dimensional electron gas
No full textWe study the spin polarization and its associated spin-Hall current due to electric-dipole-induced spin resonance in disordered two-dimensional electron systems. We show that the disorder-induced damping of the resonant spin polarization can be strongly reduced by an optimal field configuration that exploits the interference between the Rashba and Dresselhaus spin-orbit interactions. This leads to a striking enhancement of the spin susceptibility while the spin-Hall current vanishes at the same time. We give an interpretation of the spin current in geometrical terms which are associated with the trajectories the polarization describes in spin space
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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