1,721,016 research outputs found
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
Epidermal growth factor signaling in zebrafish fin regeneration
No full textThe zebrafish Danio rerio possesses a high capacity for regeneration. While the loss of a limb is permanent in mammals, zebrafish can completely restore lost appendages. The caudal fin quickly and reliably regenerates after amputation to its previous size. Previous drug studies indicate that EGFR signaling is required for osteoblast dedifferentiation, an important cellular mechanism during regeneration. This thesis further analyzes the potential role of EGFR signaling in zebrafish fin regeneration, going beyond the use of drugs by using transgenic fish lines manipulating EGFR signaling.
Using the transgenic line hs:TGFα, EGFR signaling was overactivated and effects on osteoblast dedifferentiation, regenerative length and osteoblast migration were analyzed. To have more options to examine the effects of the EGFR on several aspects of fin regeneration, new tools for tissue specific EGFR manipulation were tested. The dominant negative EGFR and constitutive active EGFR constructs were functional and used to create Cre responder lines. Using immunofluorescence against the phosphorylated EGFR (pEGFR), it could further be shown that the activated EGFR is located in the epidermal layer of the skin in the fin
The Role of BMP signaling in DNA-damage responses during zebrafish heart regeneration
No full textThe cardiomyocytes of zebrafish can regenerate in case of necrosis. Several studies have shown that the Bone morphogenetic signaling pathway (BMP signaling) is involved in the process of zebrafish heart regeneration. To identify candidate mediators of BMP signaling action on alleviation of genomic stress, the heat shock protein-mediated BMP transgenic zebrafish were used to achieve BMP signaling upregulation after cryoinjury and then the qPCR technology was used to test the expression of related genes during heart regeneration. Interestingly, my results show that cyclin dependent kinase 1 (cdk1) is upregulated upon overexpression of BMP signaling in regenerating hearts in a regeneration specific manner. I found that cdk1 could be a downstream target of BMP signaling, and there is difference gene expression between zebrafish and human cells. Further research on the molecular control of cardiac regeneration can use our findings as a starting point
Investigation of the extent of cardiomyocyte regeneration in the injured zebrafish heart and the role of Wnt signaling during cardiac repair
No full textUnlike mammals, zebrafish can achieve scar-free healing of heart injuries, which is associated with dedifferentiation and cell cycle re-entry of cardiomyocytes. However, it is unknown to which extent cardiomyocytes lost to injury are restored, since only indirect evidences of myocardial regeneration exist thus far. In addition, while Wnt signaling has been shown to induce fibrosis and prevent production of new cardiomyocytes in the infarcted murine heart, involvement of this pathway in zebrafish cardiac regeneration has not been yet investigated. Hence, we set out to provide the first absolute quantification of cardiomyocyte numbers before and after injury in zebrafish, as well as to address whether Wnt signaling impinges on cardiomyocyte proliferation and wound healing.
Firstly, we used stereological methods to quantify the number of cardiomyocytes on heart sections at 3, 14, 30 and 90 days post cryoinjury. Based on histological markers, we investigated the morphology of the regenerated myocardium. Secondly, we performed quantitative PCR and in situ hybridization to check whether Wnt signaling is active, and which Wnt ligands are expressed in the injured heart. Finally, we employed genetic tools for Wnt/β-catenin manipulation and measured proliferation and dedifferentiation in cardiomyocytes, as well as wound resorption, upon inhibition of the pathway.
We found that injured zebrafish hearts did regenerate to the pre-injury number of cardiomyocytes already within four weeks. Mathematical modeling indicated that all cardiomyocytes that enter the cell cycle at the wound border actually proliferate. The regenerated myocardium does not display signs of altered morphology compared to uninjured hearts. Thus, we establish that zebrafish can indeed completely and faithfully regenerate the ventricular myocardium. Surprisingly, full cardiomyocyte regeneration also occurred in hearts that retained scars, indicating that cardiomyocyte regeneration is more efficient than scar-free healing. In addition, we found that Wnt/β-catenin signaling is active in regenerating hearts both in cardiomyocytes and in endothelial cells. Blockade of the pathway impairs cardiomyocyte dedifferentiation and proliferation, likely in a cell autonomous manner. However, Wnt signaling has no significant effect on scar removal. Finally, we found significant upregulation of the Wnt9a ligand in endothelial cells after injury.
Our results show that zebrafish cardiomyocyte regeneration is efficient and complete, and it does not require complete scar removal. Wnt/β-catenin is an important player in this process, since it is required to promote cell cycle re-entry and dedifferentiation of pre-existing cardiomyocytes
Effekt des Hitzeschockproteins HspB5/alpha-B-Crystallin auf den basalen Dendritenbaum hippocampaler Pyramidenzellen der Maus
No full textDer Dendritenbaum von Neuronen ist entscheidend für Informationsaufnahme, Integration von Signalen, Signalverarbeitung und damit Kommunikation zwischen Neuronen. Die meisten neurodegenerativen Erkrankungen sind durch eine rarefizierte Dendritenarchitektur gekennzeichnet, welche mit neuronaler Dysfunktion und Abnahme der kognitiven Fähigkeiten der Patienten einhergeht. HspB5 wird bekannterweise bei neurodegenerativen Erkrankungen in den betroffenen Gehirnarealen hochreguliert und phosphoryliert. Weiterhin ist beschrieben, dass HspB5 in dissoziierten hippocampalen Neuronenkulturen die Komplexität des Dendritenbaums steigern und bei Schädigung diesen stabilisieren kann. In der vorliegenden Arbeit wurde dieser dendritische Effekt von HspB5 in vivo näher untersucht. Zunächst wurde mittels indirekter Immunfluoreszenz gezeigt, dass HspB5 in Neuronen des Hippocampus exprimiert wird und dort zelltyspezifisch in verschiedenen subzellulären Kompartimenten phosphoryliert wird. Mittels in utero Elektroporation wurden HspB5 und die nicht-phosphorylierbare Mutante HspB5-AAA in Pyramidenzellen der CA1-Region von Mäuseembryonen an Embryonaltag 15 transfiziert und überexprimiert. Postnatal an Tag 15 wurden die Gehirne entnommen und in Gehirnschnitten die Dendritenbäume der Pyramidenzellen immunhistochemisch dargestellt. Mittels konfokaler Mikroskopie,Tracing des Dendritenbaums mit Imaris-Software und Anfertigen von Sholl-Analysen erfolgte die Analyse basaler Dendritenbäume der CA1- Region. HspB5 exprimierende Neurone zeigten eine erhöhte Anzahl der Schnittpunkte der Sholl-Ringe verglichen mit HspB5-AAA und die Kontrolle exprimierenden Neuronen. Das Signifikanzniveau (p < 0,05) wurde bei einem Sholl-Ring (45 μm) zwischen HspB5 und HspB5-AAA erreicht. Dieser beobachtete Trend bestätigte sich in der größeren Gesamtlänge und der erhöhten Anzahl der Endpunkte für HspB5 exprimierende Neurone. Die Mutante HspB5-AAA wies in der Sholl-Analyse eine ähnliche Anzahl der Schnittpunkte mit den Sholl-Ringen auf wie die Kontrolle.
Somit konnte der in vitro beobachtete Effekt von HspB5 auf den Dendritenbaum in dieser Arbeit in vivo bestätigt werden. Es kann die Hypothese formuliert werden, dass die Hochregulation und Phosphorylierung von HspB5 bei neurodegenerativen Erkrankungen möglicherweise einen endogenen Schutzmechanismus darstellt, der den Erhalt der Dendritenmorphologie zum Ziel hat
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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