1,720,984 research outputs found
Monitoring the microtubule nucleation dynamics of sperm centriole after IFV and ICSI in sheep zygotes.
Get PDFIntracytoplasmic sperm injection (ICSI) is an assisted reproductive (ART) technique that is less efficient in ruminant, comparing to other species. In mammals, the spermatozoa proximal centriole nucleates the microtubule and generates the functional cell centriole of the resulting organism. Our study aimed to investigate eventual difference in the centriole microtubular nucleation in ICSI fertilized oocytes, comparing to control In Vitro Fertilized ones (IVF). In fact, we made the hypothesis that the tail severing step achieved in our ICSI protocol through applying a few piezo pulses, might mechanically damage the proximal centriole. On this basis, Sheep oocytes were in vitro maturated (IVM) for 24 h then were injected by piezo-pulsed spermatozoa, chemically activated by 5 min of incubation with 5 mg/ml ionomycin, washed in H199 for 5 min and cultured in 50 μl drops of Synthetic Oviductal Fluid (SOF) with estrus sheep serum and 16 μM isoproterenol, covered by mineral oil. Fertilization has been arrested around 5h after ICSI, and the presumptive zygotes were processed for immunological detection of tubulin. Zona Pellucida (ZP) was removed with a combined treatment of acid Tyrode and trypsin and zygotes were then fixed with 4% paraformaldehyde (pH7.2) and permeabilized by 0.5% Triton X-100, for 20 min each. Microtubular nucleation was assessed with anti-α-tubulin immunofluorescence under confocal microscopy. No difference was noticed in the dynamics and timing of sperm microtubular aster nucleation, that started around 5h post ICSI (5h30). Therefore, we conclude that abnormal microtubular nucleation by the centriole is not responsible for the low development of ICSI fertilized sheep oocytes
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
Reducing the time of spermatozoa/oocyte interaction improves embryonic development in sheep.
No full textIn vitro fertilization (IVF) is a well-established Assisted Reproductive Technique (ART) routinely applied in human infertility treatment and in large animals, both to boost reproductive performances of selected genotypes, and also for basic research. Despite its value, IVF has seen very little progress in the last two decades, and relies to established paradigms, like overnight sperm-egg co-incubation. However, the long exposure to the relatively high spermatozoa concentration in a dish increases the risk of polyspermy and could be detrimental for early embryonic development.
In our work we have identified the time window within which the fertilization occurs in order to refine the procedure and reduce sperm-egg co-incubation, comparing embryo development after short (sIVF) and overnight spermatozoa/oocyte co-incubation (o/nIVF).
A total of 144 in vitro matured sheep oocytes were co-incubated with spermatozoa in IVF medium [synthetic oviductal fluid (SOF) with 20% oestrus sheep serum and 16μM isoproterenol]. Then, small batches of oocytes were collected every 30 minutes to check for the presence of a fertilizing spermatozoon. To assess that, cumulus cells were removed and presumptive fertilized oocytes were fixed and stained with propidium iodide for nuclei and Pisum sativum agglutinin for zona pellucida (ZP) detection respectively. Pronuclear formation (PN) and embryo development were evaluated after 16 hours (PN), 24 hours (2 cells) and 7 days of culture (blastocyst).
We found that spermatozoa engaged with the ZP not earlier than 90 minutes and penetrated the oocytes within 3-4 hours after IVF. A trend for a lower polyspermic fertilization (>2PN) was detected in sIVF (7.7%) vs o/nIVF (18.4%,). Likewise, cleavage and blastocyst rate were higher after sIVF compared to o/n-IVF (2-cells: 38.6% vs 23.8%; blastocyst: 18.1% vs 9.5%; sIVF vs o/nIVF).
This work demonstrates that 4 hours spermatozoa/oocyte interaction are sufficient to achieve fertilization, reduce polyspermy and improve early embryonic development in sheep
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
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
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