1,720,987 research outputs found
Early-Stage Evolution of the Neo-Y Chromosome in Drosophila albomicans
No full text在許多物種中，其性染色體都是由同源體染色體演化而來。一般來說， Y 染色體喪失了性別決定因子外大部份的基因， X 染色體卻保留原本染色體上的基因 。由於在 XY 染色體之間停止互換，導致有害突變累積，因此造成 Y 染色體的退化。 在晚近形成的新性染色體中，屬於原體染色體的部份可供我們研究同源染色體演化為性染色體的過程。為了探究早期新性染色體的演化，我們比較具有新性染色體的紅果蠅中序列的差異和全轉錄體的模式。我們發現，雖然大部份的轉錄序列仍然有很強的負向選汰，但在 2344 個轉錄序列中，分別有 11.5% 和 2.7% 的轉錄序列顯示位於新 Y 基因座和新 X 基因座的基因表現量明顯下降。新性染色體表現量的分歧，是由於新 X 基因座過量表現以及新 Y 基因座表現量降低所造成的。此外，我發現這些具有表現量分歧的基因在新 X 和新 Y 基因座的序列間具有較高的差異。進而我們觀察到向來在雌性表現都較高的基因，其新 Y 基因座表現量往往降低；相反的，新 Y 基因座表現量升高會使基因在雄性中表現較高。我的結果顯示基因表現量在新性染色體的分歧在早期新性染色體演化扮演重要的角色。Sex chromosomes evolved independently from autosomes in various lineages. In general, Y chromosome lost most of its genes except for sex determination factors while X chromosome remains gene-rich. The degeneracy of Y-linked genes is caused by accumulation of deleterious mutations as a consequence of recombination inhibition between the sex-chromosome pairs. To decipher the transition from homologous autosomes to differentiated sex chromosomes, the recently fused autosomal regions of the neo-sex chromosomes in Drosophila albomicans provide a good model. Both of its sequence divergence and whole transcriptome profiles were compared to understand the early neo-sex chromosome evolution. I find that most neo-X and neo-Y linked alleles remain under purify selection (dN/dS=0.001/0.021). However, among 1,798 transcripts, 19.0% and 4.0% show significantly reduced gene expression in neo-Y and neo-X linked alleles, respectively. The expression divergence between neo-sex alleles was attributed to both upregulation of neo-X alleles and downregulation of neo-Y. In addition, the genes with expression divergence would have larger sequence divergence between neo-sex alleles. Further analyses reveal that old female-biased genes were prone to reduce the expression of neo-Y alleles, whereas upregulation of neo-Y alleles might shape new male-biased genes. My results indicate that the expression divergence between neo-sex chromosomes is an important step of ealy neo-sex chromosome evolution in D. albomicans
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
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
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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