1,720,972 research outputs found
Model for Triplet-Triplet Energy Transfer in Natural Clusters of Peridinin Molecules Contained in "Dinoflagellate"'s Outer Antenna Proteins.
No full textTriplet-triplet energy transfer among peridinin molecules in peridinin-chlorophyll-protein (PCP) complexes from two different dinoflagellate species is quantitatively evaluated by the use of the optically detected magnetic resonance technique supplemented by triplet-state decay rate measurements. The two complexes are related by a dimer-monomer relationship in the sense that the four peridinins-one chlorophyll cluster of the Heterocapsa pygmeae PCP (H-PCP) is a copy of the two clusters contained in the larger protein Amphidinium carterae PCP (A-PCP), which are related by a local 2-fold symmetry axis. The system is conveniently discussed as a multistate Frenkel exciton system performing stochastic jumps from one exciton state to another. The rate of triplet-triplet energy exchange among peridinin molecules is obtained through the simulation of the spectral line shapes of optically detected magnetic resonance in zero field. Measurements were collected in a range of temperatures between 2 and 40 K and supplemented by the determination of the decay rate of the triplet to ground state in the same temperature range. The latter is of the order of 0.005 MHz and is relevant in determining the line shapes, especially at the lowest temperatures where the exchange rates are low. Exchange rates within the four-member peridinin cluster of H-PCP exactly match those within each of the two clusters of A-PCP and span a range from 0 to 20 MHz for the uphill rate and from 10 to 300 MHz for the downhill rate, corresponding to an energy difference of 41 cm(-1). The intercluster exchange rate in A-PCP goes from 0 to 12 MHz uphill and from 0.05 to 30 MHz downhill, with an energy difference of only 12.5 cm(-1). The kinetics conform to phonon-stimulated radiationless transition theory, and coupling parameters and reorganization energies are evaluated and discussed
OPTICALLY DETECTED MAGNETIC-RESONANCE STUDY ON THE ORIGIN OF THE PHEOPHYTIN TRIPLET-STATE IN D1/D2 CYTOCHROME B-559 COMPLEXES
No full textIn order to determine the origin of the photoexcited pheophytin triplet state ((3)Phe) in plant Photosystem II preparations (D1/D2-cyt b-559 complexes) an absorption and fluorescence detected magnetic resonance (ADMR, FDMR) study was conducted in zero magnetic field at low temperatures. The ADMR signal intensity dependence on excitation light flux was linear showing that (3)Phe is formed by a 1-photon process. Upon successive exposure of the sample to strong white light it was shown that (3)Phe is not directly correlated with the primary donor triplet state (3)P680. This is consistent with the absence of a double resonance signal connecting (3)Phe with (3)P680 down to an instrumental sensitivity of Delta I/I (Delta transmission/transmission) below 10(-6). An intermediate state of photoinhibition between intact and fully degraded reaction centres is responsible for the formation of (3)Phe. It may be a conformationally changed state of the reaction centre protein, most likely having a larger distance between P680 and the pheophytin whose triplet state is observed. Factor analysis of the absorption spectra of a series of gradually degraded samples yielded two spectral components which were interpreted as the spectra of fully intact and completely degraded reaction centres
ODMR OF CAROTENOID AND CHLOROPHYLL TRIPLETS IN CP43 AND CP47 COMPLEXES OF SPINACH
No full textOptically detected magnetic resonance (ODMR) of the light-harvesting complexes CP43 and CP47 of the spinach photosynthetic machinery revealed triplet stales both from carotenoids and chlorophylls. The triplet state of the only carotenoid present in the complexes (beta-carotene) is observed by ODMR using fluorescence detection (FDMR) in the main chlorophyll emission band in the 680 nm region, and absorption detection in the visible region. Chlorophyll triplet signals arc also obtained by microwave sweeping in the chlorophyll emission and absorption regions. MIA spectra are obtained and discussed for both complexes
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
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