1,720,954 research outputs found
The xanthophyll cycle balances photoprotection and photosynthetic efficiency in the seawater alga Nannochloropsis oceanica
No full textPhotosynthetic reactions are continuously modulated to respond to highly dynamic environmental conditions. Balancing photosynthesis and photoprotection involves various mechanisms, which differ across phylogenetic groups. One such mechanism that is widespread in photosynthetic eukaryotes is the xanthophyll cycle, which involves the reversible light-dependent conversion between the carotenoids violaxanthin, antheraxanthin, and zeaxanthin. In this study, we investigated the role of the xanthophyll cycle in Nannochloropsis oceanica, a seawater microalga that possesses peculiarly high xanthophyll levels. To this end, we generated and characterized lines with increased levels of the enzymes involved in the xanthophyll cycle, i.e. violaxanthin de-epoxidase (VDE) and zeaxanthin epoxidase (ZEP). We demonstrated that the level of VDE and ZEP is the main factor controlling the overall reaction rates and dynamics of the xanthophyll cycle. Subsequent differences in the xanthophyll profile affect the activation of photoprotection mechanisms such as nonphotochemical quenching and tolerance to reactive oxygen species. Interestingly, VDE overexpression enhances high light tolerance, whereas increased ZEP levels facilitate faster recovery after light exposure but also heighten photosensitivity under certain conditions. In addition, light exposure strongly downregulates ZEP activity in Nannochloropsis. Taken together, these findings underscore the critical role of the xanthophyll cycle in regulating photosynthesis in Nannochloropsis. This cycle is not simply a mechanism that responds to excess illumination, but one that balances photoprotection and light-use efficiency under different environmental conditions
Modulation of the xanthophyll cycle improves biomass productivity and light tolerance of the microalga Nannochloropsis oceanica
No full textMicroalgae in photobioreactors encounter highly diverse light conditions along the culture depth because of cellular self-shading. Culture mixing also causes individual cells to rapidly shift from darkness to strong illumination, causing oversaturation of the photosynthetic apparatus and damage. Moreover, travelling from high light to darker layers can lead to energy loss through photoprotective mechanisms that remain active even when not needed. In the microalga Nannochloropsis oceanica the xanthophyll cycle plays a central role in the regulation of light harvesting and photoprotection, making it a central target for the optimization of photosynthetic performances in photobioreactors. Recently, we showed that the genetic control of the accumulation of enzymes that regulate the xanthophyll cycle, violaxanthin de-epoxidase (VDE), and zeaxanthin epoxidase (ZEP), can dramatically accelerate its kinetics. In this study, we characterized the impact of VDE and ZEP on the growth of N. oceanica. We monitored biomass productivity, pigment content, and photosynthetic performances, comparing single with double overexpressors in limiting and excess light conditions, in both tubular and flat panel photobioreactor systems. The acceleration of the xanthophyll cycle activation by increased accumulation of VDE led to increased photoprotection and enhanced light tolerance, but also excessive energy dissipation in limiting light. The enhancement of the xanthophyll cycle relaxation through ZEP accumulation, instead, reduced energy losses but could also increase photosensitivity. The combination of the two approaches resulted in the greatest benefit, leading to an improved productivity across different photobioreactor geometries and light conditions
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
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
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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