1,721,290 research outputs found
Correction to: CT angiography vs echocardiography for detection of cardiac thrombi in ischemic stroke: a systematic review and meta-analysis (Journal of Neurology, (2020), 267, 6, (1793-1801), 10.1007/s00415-020-09766-8)
No full textThe original version of this article unfortunately contained a mistake. In the author list, the first and last names of two authors, S. Matthijs Boekholdt and R. Nils Planken, were tagged incorrectly. Therefore, author names are abbreviated wrongly in Springerlink. The first and last names should be as follows: First name: S. Matthijs Last name: Boekholdt First name: R. Nils Last name: Planken
Probing excitons with time-resolved momentum microscopy
No full textExcitons – two-particle correlated electron-hole pairs – are the dominant low-energy optical excitation in the broad class of semiconductor materials, which range from classical silicon to perovskites, and from two-dimensional to organic materials. The study of excitons has been brought on a new level of detail by the application of photoemission momentum microscopy – a technique that has dramatically extended the capabilities of time- and angle resolved photoemission spectroscopy. Here, we review how the photoelectron detection scheme enables direct access to the energy landscape of bright and dark excitons, and, more generally, to the momentum-coordinate of the exciton wavefunction. Focusing on two-dimensional materials and organic semiconductors, we first discuss the typical photoemission fingerprint of excitons in momentum microscopy and highlight that it is possible to obtain information not only on the electron- but also hole-component. Second, we focus on the recent application of photoemission orbital tomography to such excitons, and discuss how this provides a unique access to the real-space properties of the exciton wavefunction. We detail how studies performed on two-dimensional transition metal dichalcogenides and organic semiconductors lead to very similar conclusions, and, in this manner, highlight the strength of momentum microscopy for the study of optical excitations in semiconductors
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
Probing excitons with time-resolved momentum microscopy
No full textExcitons -- two-particle correlated electron-hole pairs -- are the dominant
low-energy optical excitation in the broad class of semiconductor materials,
which range from classical silicon to perovskites, and from two-dimensional to
organic materials. Recently, the study of excitons has been brought on a new
level of detail by the application of photoemission momentum microscopy -- a
technique that has dramatically extended the experimental capabilities of time-
and angle-resolved photoemission spectroscopy (trARPES). Here, we review how
the energy- and momentum-resolved photoelectron detection scheme enables direct
access to the energy landscape of bright and dark excitons, and, more
generally, to the momentum-coordinate of the exciton that is fundamental to its
wavefunction. Focusing on two-dimensional materials and organic semiconductors
as two tuneable platforms for exciton physics, we first discuss the typical
photoemission fingerprint of excitons in momentum microscopy and highlight that
is is possible to obtain information not only on the electron- but also
hole-component of the former exciton. Second, we focus on the recent
application of photoemission orbital tomography to such excitons, and discuss
how this provides a unique access to the real-space properties of the exciton
wavefunction. Throughout the review, we detail how studies performed on
two-dimensional transition metal dichalcogenides and organic semiconductors
lead to very similar conclusions, and, in this manner, highlight the strength
of time-resolved momentum microscopy for the study of optical excitations in
semiconductors
Probing excitons with time-resolved momentum microscopy
No full textExcitons -- two-particle correlated electron-hole pairs -- are the dominant
low-energy optical excitation in the broad class of semiconductor materials,
which range from classical silicon to perovskites, and from two-dimensional to
organic materials. Recently, the study of excitons has been brought on a new
level of detail by the application of photoemission momentum microscopy -- a
technique that has dramatically extended the experimental capabilities of time-
and angle-resolved photoemission spectroscopy (trARPES). Here, we review how
the energy- and momentum-resolved photoelectron detection scheme enables direct
access to the energy landscape of bright and dark excitons, and, more
generally, to the momentum-coordinate of the exciton that is fundamental to its
wavefunction. Focusing on two-dimensional materials and organic semiconductors
as two tuneable platforms for exciton physics, we first discuss the typical
photoemission fingerprint of excitons in momentum microscopy and highlight that
is is possible to obtain information not only on the electron- but also
hole-component of the former exciton. Second, we focus on the recent
application of photoemission orbital tomography to such excitons, and discuss
how this provides a unique access to the real-space properties of the exciton
wavefunction. Throughout the review, we detail how studies performed on
two-dimensional transition metal dichalcogenides and organic semiconductors
lead to very similar conclusions, and, in this manner, highlight the strength
of time-resolved momentum microscopy for the study of optical excitations in
semiconductors
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