1,720,973 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
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
Structural Analysis of Three-dimensional Human Neural Tissue derived from Induced Pluripotent Stem Cells
Get PDFObjective: The present study aimed at establishing a method for production of a three-dimensional (3D) human neural tissue derived from induced pluripotent stem cells (iPSCs) and analyzing the outcome by a combination of tissue ultrastructure and expression of neural markers.Methods: A two-step cell culture procedure was implemented by subjecting human iPSCs to a 3D scaffoldbased neural differentiation protocol. First, neural fate-inducing small molecules were used to create a neuroepithelial monolayer. Second, the monolayer was trypsinized into single cells and seeded into a porous polystyrene scaffold and further cultured to produce a 3D neural tissue. The neural tissue was characterized by a combination of immunohistochemistry and transmission electron microscopy (TEM).Results: iPSCs developed into a 3D neural tissue expressing markers for neural progenitor cells, early neural differentiation and maturation, radial glial cells and cellular proliferation including SOX2, Nestin, β-III Tubulin, MAP2, Tau, BLBP and Ki67. We found an abundance of rosette structures resembling the morphology of the developing neural tube. These neural tube-like structures (NTLS) were shown to contain areas of neural progenitor cell maintenance and proliferation. The resemblance to the embryonic neural tube was further supported by TEM analyses demonstrating luminal tight junctions and primary cilia. Moreover, the NTLS consisted of radial glial-like cells, radiating from the lumen, and neural progenitor cells presenting elongated nuclei, signaling nucleus transposition seen at interkinetic nuclear migration during early neurogenesis, and mitoses.Conclusion: Our findings revealed that this relatively simple 3D scaffold-based neural differentiation protocol for human iPSCs was able to recapitulate several key events in early neural development. The organization into NTLS and the presence of mature neural cells in the tissue surrounding these structures showed that this protocol has potential for in vitro studies of neural development and disease modeling
Insulin-like growth factor 2:a modulator of anti-apoptosis related genes (<i>HSP70, BCL2-L1</i>) in bovine preimplantation embryos
Get PDFIntrinsic defects within the embryos, reflected by elevated cell death and low proliferative ability, are considered the most critical factors associated with bovine infertility. The identification of embryonic factors, which are responsible for successful embryo development, is thus critical in designing strategies for infertility intervention. In this experiment, the possible mechanisms involved in both blastomere proliferation and regulation of cell death were studied by analysis of relative expression patterns of IGF-II, BCL2-L1, BAK1, and HSP70 in 3 classes of morphological quality groups (e.g., excellent, good, and poor) of bovine blastocysts produced by IVF. Variation in total blastocyst cell numbers as well as their allocation to inner cell mass and trophectoderm lineages were also determined by differential CDX2 staining. Results showed that transcript levels for IGF-II, BCL2-L1, and the BCL2-L1/BAK1 ratio were higher in excellent- and good-quality blastocysts compared with low-quality blastocysts (P<0.01), whereas mRNA levels for HSP70 were higher in low-quality blastocyst compared with excellent-quality bovine blastocysts (P<0.05). In addition, excellent-quality blastocysts displayed not only greater total cell number but also greater mean inner cell mass/total cell number proportion than that of poor-quality blastocysts (P<0.01). The expression levels of IGF-II showed negative correlation with the levels of HSP70 (r=-0.70; P<0.05); however, the correlation of expression levels of IGF-II with both of BCL2-L1 (r=0.91; P<0.01) and the ratio of BCL2-L1/BAK1 (r=0.78; P<0.05) were highly positive. There was no correlation between the expression levels of IGF-II and BAK1 genes. In conclusion, these observations suggested that levels of endogenous IGF-II transcripts might be associated with the quality of IVF embryos by regulating either apoptosis-related genes or mitogenic actions in bovine preimplantation embryos.</p
Combination effects of epidermal growth factor and glial cell line-derived neurotrophic factor on the <em>in vitro</em> developmental potential of porcine oocytes
No full textThe developmental potential of in vitro matured porcine oocytes is still lower than that of oocytes matured and fertilized in vivo. Major problems that account for the lower efficiency of in vitro production include the improper nuclear and cytoplasmic maturation of oocytes. With the aim of improving this issue, the single and combined effects of epidermal growth factor (EGF) and glial cell line-derived neurotrophic factor (GDNF) on oocyte developmental competence were investigated. Porcine cumulus–oocyte cell complexes (COCs) were matured in serum-free medium supplemented with EGF (0, 10 or 50 ng/ml) and/or GDNF (0, 10 or 50 ng/ml) for 44 h, and subsequently subjected to fertilization and cultured for 7 days in vitro. The in vitro-formed blastocysts derived from selected growth factor groups (i.e. EGF = 50 ng/ml; GDNF = 50 ng/ml; EGF = 50 ng/ml + GDNF = 50 ng/ml) were also used for mRNA expression analysis, or were subjected to Hoechst staining. The results showed that the addition of EGF and/or GDNF during oocyte maturation dose dependently enhanced oocyte developmental competence. Compared with the embryos obtained from control or single growth factor-treated oocytes, treatment with the combination of EGF and GDNF was shown to significantly improve oocyte competence in terms of blastocyst formation, blastocyst cell number and blastocyst hatching rate (P < 0.05), and also simultaneously induced the expression of BCL-xL and TERT and suppressed the expression of caspase-3 in resulting blastocysts (P < 0.05). These results suggest that both GDNF and EGF may play an important role in the regulation of porcine in vitro oocyte maturation and the combination of these growth factors could promote oocyte competency and blastocyst quality
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
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