1,720,984 research outputs found
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
Spin-electric coupling in quantum dots and molecular magnets
Get PDFIn this thesis we study several aspects related to the dynamics of
electrons and holes in quantum dots, as well as dynamics of electron
spins in molecular magnets.
Magnetic materials and spin systems are usually probed and controlled
by magnetic fields. The techniques of spin manipulation via magnetic
fields were developed in the ESR and NMR studies. These techniques
allow for detailed study and manipulation of {\it large} collection of
spins.
Reducing the size of a device improves its properties. In case of a
prototypical magnetic device, a memory element, the smaller devices
will have shorter access times and larger capacity per unit volume,
and a smaller power absorption. Another important reason to study even
smaller devices is that a plethora of intriguing quantum effects
become manifest only when the size of a device is small
enough. Typically, the quantum effects start to be important at the
nanometer scale. At these scale, the control via magnetic fields of
individual devices becomes problematic.
Obtaining electric fields instead, that can be locally controlled and
fast switched, is a routine nowadays. The ability to move around
molecules with STM tips is just one example of for control of quantum
systems at the nanoscale with electric fields. The missing ingredient
is a mechanism that would make spins couple to electric fields. In this work I investigated precisely this issue, namely the coupling
of electric fields, either classical or quantum, to different spin
systems, like spins in quantum dots or molecular magnets.
The thesis is divided in four parts. In the first part, we investigate a new type
of spin-spin interaction, which arises due to the presence of both
Coulomb repulsion between two electrons localized in quantum dots,
and the spin-orbit interaction in the host material (GaAs). We show
that this type of coupling is long-range and resembles the interaction
of two electric dipoles that depend on spin. For this interaction to
arise direct coupling between electrons is not necessary (no tunneling
assumed). In the second part we investigate the interaction between spins
localized in quantum dots mediated by the electromagnetic modes of a
one dimensional microwave cavity and spin-orbit interaction. We show
that this interaction can be strong and long range ( mm), and
can be controlled (switched on and off) either magnetically or
electrically. The third part is devoted to hole-spin dynamics in quantum dots. We analyze the weak magnetic field regime of the
relaxation of a heavy-hole spin localized in a quantum dot. Driven by
recent experiments, we show that two-phonon processes give a good
explanation for the saturation of the relaxation time at intermediate
temperatures. In the fourth part we show, by several methods, that spin
transitions in (some) molecular magnets can be induced by electric
fields. We identify a spin-electric coupling caused by an interplay
between spin exchange, spin-orbit interaction, and the chirality of
the underlying spin texture of the molecular magnet. This coupling
allows for the electric control of the spin (qubit) states, e.g. by
using an STM tip or a microwave cavity. We propose an experimental
test for identifying molecular magnets exhibiting spin-electric
effects
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
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
Braiding of Majorana Fermions in a Cavity
No full textInternational audienceWe study the dynamical process of braiding Majorana bound states (MBS) in the presence of the coupling to photons in a microwave cavity. We show theoretically that the π/4 phase associated with the braiding of MBS, as well as the parity of the ground state are imprinted into the photonic field of the cavity, which can be detected by dispersive readout techniques. These manifestations are purely dynamical, they occur in the absence of any splitting of the MBS that are exchanged, and they disappear in the static setups studied previously. Conversely, the cavity can affect the braiding phase, which in turn should allow for cavity controlled braiding
Cavity magnonics with domain walls in insulating ferromagnetic wires
Get PDFMagnetic domain walls (DWs) are topological defects that exhibit robust
low-energy modes that can be harnessed for classical and neuromorphic
computing. However, the quantum nature of these modes has been elusive thus
far. Using the language of cavity optomechanics, we show how to exploit a
geometric Berry-phase interaction between the localized DWs and the extended
magnons in short ferromagnetic insulating wires to efficiently cool the DW to
its quantum ground state or to prepare nonclassical states exhibiting a
negative Wigner function that can be extracted from the power spectrum of the
emitted magnons. Moreover, we demonstrate that magnons can mediate long-range
entangling interactions between qubits stored in distant DWs, which could
facilitate the implementation of a universal set of quantum gates. Our proposal
relies only on the intrinsic degrees of freedom of the ferromagnet, and can be
naturally extended to explore the quantum dynamics of DWs in ferrimagnets and
antiferromagnets, as well as quantum vortices or skyrmions confined in
insulating magnetic nanodisks.Comment: 5 pages+Supplemental Material; 6 figure
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