1,720,979 research outputs found
Monitoring oxidative damage responses in Daucus carota cell lines: contribution of DNA topoisomeras I
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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
Lack of enantioselectivity of herpes virus thymidine kinase allows safer imaging of gene delivery
No full textHerpes simplex virus thymidine kinase (HSV-TK) is widely used in gene therapy. The enzymatic activity of HSV-TK may be traced in vivo by specific radiopharmaceuticals in order to image transgene expression. However, most of these radiopharmaceuticals are toxic per se or after activation by HSV-TK, and therefore do not represent ideal molecules for clinical applications and repeated imaging. Unlike human cytosolic TK, HSV-TK is not enantioselective and can efficiently phosphorylate both D and L enantiomers of beta-thymidine. Here we show that, after phosphorylation by HSV-TK, tritiated L-beta-thymidine (LT) is selectively retained inside the cells in vitro and in vivo. We used the in vivo accumulation of radioactive phosphorylated LT to image the HSV-TK-positive cells inside a transplantable murine brain tumour after inoculation of cells producing retroviruses carrying HSV-TK. Owing to their unnatural enantiomeric conformation, phosphorylated LT metabolites are very poorly processed by mammalian enzymes, thus leading to increased cellular retention and minimal toxicity. The ability to image cells expressing the HSV-TK gene by using radiolabelled LT, without damaging the cells accumulating the phosphorylated L-nucleoside, will be important to monitor the levels and spatial distribution of therapeutic vectors carrying HSV-TK
Novel nonsubstrate inhibitors of human thymidine phosphorylase, a potential target for tumor-dependent angiogenesis
No full textThymidine phosphorylase/platelet-derived endothelial cell growth factor (TP/PD-ECGF) is an enzyme involved in thymidine metabolism and homeostasis, and its catalytic activity appears to play an important role in angiogenesis. Here we describe the cloning and expression of a His-tagged human TP/PD-ECGF and its assay with uracil and thymine analogues. We present the design, synthesis, and biological evaluation of novel 6-(phenylalkylamino)uracil derivatives which, at micromolar concentrations, inhibit both catabolic and anabolic reactions of human TP in vitro. These base analogues are not converted by the enzyme into the nucleoside form, thus representing pure nonsubstrate inhibitors of the enzyme
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
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