1,720,992 research outputs found
Structure, function and regulation of plant photosystem I.
No full textPhotosystem I (PSI) is a multisubunit protein complex located in the thylakoid membranes of green plants and algae, where it initiates one of the first steps of solar energy conversion by light-driven electron transport. In this review, we discuss recent progress on several topics related to the functioning of the PSI complex, like the protein composition of the complex in the plant Arabidopsis thaliana, the function of these subunits and the mechanism by which nuclear-encoded subunits can be inserted into or transported through the thylakoid membrane. Furthermore, the structure of the native PSI complex in several oxygenic photosynthetic organisms and the role of the chlorophylls and carotenoids in the antenna complexes in light harvesting and photoprotection are reviewed. The special role of the 'red' chlorophylls (chlorophyll molecules that absorb at longer wavelength than the primary electron donor P700) is assessed. The physiology and mechanism of the association of the major light-harvesting complex of photosystem II (LHCII) with PSI during short term adaptation to changes in light quality and quantity is discussed in functional and structural terms. The mechanism of excitation energy transfer between the chlorophylls and the mechanism of primary charge separation is outlined and discussed. Finally, a number of regulatory processes like acclimatory responses and retrograde signalling is reviewed with respect to function of the thylakoid membrane. We finish this review by shortly discussing the perspectives for future research on PSI
Red Spectral Forms of Chlorophylls in Green Plant PSI- A Site-Selective and High-Pressure Spectroscopy Study
No full textOne of the special spectroscopic characteristics of photosystem I (PSI) complexes is that they possess absorption and emission bands at lower energy than those of the reaction center. In this paper, the red pigment pools of PSI-200, PSI-core, and LHCI complex from Arabidopsis thaliana have been characterized at low temperatures by means of spectrally selective (hole-burning and fluorescence line-narrowing) and high-pressure spectroscopic techniques. It was shown that the green plant PSI-200 complex has at least three red pigment pools, from which two are located in the PSI-core and one, in the peripheral light-harvesting complex I (LHCI). All of the red pigment pools are characterized by strong electron-phonon coupling. A Huang-Rhys factor of 2.9 found for the red pigments of LHCI is the largest found for any photosynthetic antenna system. This contrasts with the bulk pigments in the main Qy absorption band of chlorophyll a pigments for which the Huang-Rhys factors of less than unity are observed. This electron-phonon coupling difference of the red and bulk pigments is well reflected by the spectral dependence of the hole-burning efficiency, which is significantly reduced in the red absorption region. As a result of extremely low hole-burning efficiency in the red absorption band of LHCI, the hole-burning spectra of the PSI-200 complex mainly originate from the red pigments of the PSI-core complex. At the same time, the source of the red emission in PSI-200 is the red pigments of LHCI, in agreement with previous studies. The hole-burning spectra of PSI-core complexes from green plant and cyanobacteria are similar, both in red and bulk absorption regions. High-pressure spectroscopy data reveal dramatically larger pressure-induced linear shift rates for the redmost absorption and emission bands relative to those of bulk absorption bands. This is interpreted as due mostly to increased conformational mixing between the locally excited and charge transfer configurations of the red pigment aggregates. On the basis of analysis of available experimental data, we suggest that pigment dimers are probably responsible for the redmost states. Consequently, the excited red states can be interpreted as excimer states
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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