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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
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A novel role for free tubulin oligomers in cross-linking tau-mediated microtubule bundles: A structural study on protein assembly states
Get PDFMicrotubules are self-assembling cytoskeletal protein structures composed of tubulin dimer subunits and are ubiquitous in mammalian cells, where they serve a multitude of functions such as maintaining cellular shape, providing pathways for intracellular transport, and driving neuronal outgrowth in early development. Their ability to elongate with the addition of tubulin, shorten by peeling away individual or oligomeric subunits, and switch between these two states is called dynamic instability and provides a focal point for cellular regulation of microtubule-driven processes. Indeed, many microtubule-associated proteins (MAPs) are known to bind microtubules and alter dynamic instability by promoting or suppressing either the polymerization or depolymerization of individual microtubules. One heavily studied MAP is tau, an intrinsically disordered protein primarily localized to the axonal compartment of mature neurons. Scientific focus on the properties and function of tau stems from the discovery many decades ago of neurofibrillary tangles as a hallmark of Alzheimer’s disease and, later of tau’s involvement in those tangles and in several other neurodegenerative diseases. Pathological and physiological roles for tau have been studied extensively. For example, we know that different tau isoforms are differentially expressed in development and maturity, that tau binds to and modifies microtubule dynamic instability, and that chemical alterations to tau leading to dysfunction are sufficient to induce disease-like pathology in cell cultures, animal studies, and humans. One poorly understood tau function is its ability to mediate the phase separation and regular spacing of microtubules in string-like arrays or bundles. Such microtubule structures are found at the axon initial segment of mature neurons, where they are referred to as “fascicles,” and have been re-produced with the addition of tau in non-neuronal cell cultures and in cell-free protein experiments involving only tubulin and recombinant human tau. Interestingly, the sorting of tau to the axon has been shown to rely on the structural integrity of the AIS, including microtubules, and is dependent on binding of tau to microtubules, implying a possible link between tau-mediated microtubule bundling and the subcellular localization of tau itself. Thus, imperative to understanding the physiological relevance of tau-mediated microtubule bundling is determining the mechanism by which tau mediates inter-microtubule interactions within bundles.
Several models have been proposed, creating a dogma of tau-tau interactions driving bundling, but are incompatible with polyelectrolyte theory and the structural features of microtubule bundles, namely wall-to-wall distances between neighboring microtubules. To better understand the underlying mechanism of tau-mediated bundling, we sought to monitor the structures of microtubule bundles as a function of time in the presence of several factors or conditions we thought would alter the interactions underlying bundle formation. First, experiments were designed to probe the electrostatic-component of tau-mediated bundling. Several tau-tau models for microtubule bundling rely on the dipole-like distribution of charge along tau’s N-terminal tail, where a relative abundance of acidic residues are followed by an abundance of basic residues, providing a possible mechanism for two opposing tau molecules to overlap and favorably interact to hold adjacent microtubules together. By increasing the ionic strength of the buffers, we sought to weaken such charge-charge interactions, which would predict a decrease in bundling strength or an outright inability of tau to mediate bundle formation in high-salt buffers. Instead, our data show that wall-to-wall distances between microtubules is largely unaffected by increases in monovalent cation species. Interestingly, with the addition of excess divalent cations, Mg2+ or Ca2+, an unexpected transformation of the hexagonal bundle lattice was observed. Specifically, we found that above threshold concentrations of either divalent cation, a phase transition is induced as a function of time or increased cation content. The phase transition is marked by the sudden and simultaneous drop in average wall-to-wall spacing, increase in lattice parameter (bundle size, or number of microtubules per bundle), and proliferation of inverted tubulin rings.
Based on these results, we propose and test a model where free tubulin oligomers participate in and are necessary for the bundling of microtubules by tau protein. In our model, tau binds to multiple species of tubulin to join together free (non-lattice-bound) tubulin oligomers and lattice-bound tubulin within microtubules. The multivalent nature of tau’s interactions with various tubulin oligomers and microtubules creates a network of tubulin and tau that cross-links microtubules within bundles. Within this model, an absence or depletion of free tubulin should prevent tau-mediated bundling, while increases to the free tubulin content should enhance bundle properties. Consistent with this model, experiments designed to induce rapid microtubule depolymerization by dropping the sample temperature reproduced the phase transitions observed in the depolymerization events induced by divalent cations. Similarly, samples prepared with increasing GTP content showed resistance to microtubule depolymerization over time, corresponding to the delay and in some cases elimination of the phase transition. Taken together, our results and the model we propose for tau-mediated microtubule bundling represent a novel role for tubulin in the bundling process. We are excited by the prospect of these new findings and their physiological relevance both to the understanding of developmental and mature tau function in human neurons but also to tau dysfunction in neurodegenerative diseases
A novel role for free tubulin oligomers in cross-linking tau-mediated microtubule bundles: A structural study on protein assembly states
No full textDispelling 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
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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