161,020 research outputs found
Life at elevated CO2 modifies the cell composition of Chromera velia
No full textWe investigated the response to high CO2 of Chromera velia, a photosynthetic relative of apicomplexan parasites that is possibly involved in symbiotic associations with scleractinian corals. The inorganic C content in the proximity of the symbiotic algal cells within the tissues of scleractinians is disputed. According to some authors, it is very high. A higher C content in the endodermal tissues of scleractinians than in the external environment may have favoured the constitution of symbiosis with organisms such as Symbiodinium and Chromera that have a type II Rubisco, which is intrinsically ill suited to low CO2 environments. We thus cultured C. velia at the very high inorganic C estimated by some authors and assessed its growth and photosynthetic performance. We also evaluated whether these conditions affected C allocation and elemental stoichiometry in C. velia cells by state-of-the-art Fourier transform infrared spectroscopy and total reflection X-ray fluorescence spectrometry in combination with more traditional biochemical and physiological techniques. Our results demonstrated that C. velia was capable of coping with very high CO2, which even stimulated biomass production and increased N, P, Mn, Fe and Zn use efficiency. Growth at elevated CO2 changed the stoichiometric relationships among elements in C. velia cells, but had no effect on the relative abundance of the main organic pools. The high CO2 in the animal tissue surrounding the photosynthetic cells may therefore facilitate C. velia life in symbiosis
Does growth rate affect diatom compositional response to temperature?
No full textTemperature is one of the environmental factors that most strongly influence the life of microalgae, from the enzymatic level up to the modification of biosynthetic and degradation potential and, thus, cellular composition. When exposed to a change in environmental milieu two main responses can be attained by cells: acclimation or homoeostasis. Recent studies testing the impact of other environmental factors indicated that the choice between these strategies is related to growth rates, i.e. cells dividing at a faster rate showed inclination to acclimation while cells dividing at a slower rate were more prone to homoeostasis. These findings motivated us to further explore the extent to which these compositional response modes are applied under varying temperature. Two representative marine diatoms, one centric, Thalassiosira pseudonana, and one pennate, Cylindrotheca fusiformis were investigated. Species were cultured at 15°C, 20°C and 30°C and at two growth rates. Compositional response was analysed with respect to elemental stoichiometry (carbon, nitrogen, silica, phosphorus, sulphur, manganese, iron, zinc and copper) and the major organic pool ratios (carbohydrate:lipid, carbohydrate:protein and protein:lipid). While T. pseudonana exhibited an acclimation response to temperature, C. fusiformis proved to be strongly homoeostatic. In the case of T. pseudonana, our data showed that the variations in composition were consistent with the growth rate dependence hypothesis for many micronutrients, but not for carbon and nitrogen contents, and C:N ratio. These species-specific differences in response mode highlight the diversity in ecophysiological strategies of diatoms, which needs to be considered when predicting climate change responses
The phycobilisomes of Synechococcus sp. are constructed to minimize nitrogen use in nitrogen-limited cells and to maximize energy capture in energy-limited cells
No full textSynechococcus sp. UTEX LB2380 is a coastal strain of a cosmopolitan cyanobacterial genus. In coastal waters, N and light availability are highly variable and their
interplay may influence C allocation and photosynthetic performance. In this paper, we compared the impact of nitrogen (N) limitation and energy (light, E) limitation on
phycobilisome composition and photosynthesis, in the presence of either NO3- or NH4+. Our hypothesis was that the phycobilisome composition would be influenced
by the factor limiting growth. Our results show that N-limited cells adjusted their phycobilisome antenna to minimize N utilization, whereas E-limited cells had a
phycobilisome composition tailored to alleviate E deficiency. The N-source was relevant for the pigment composition, under both limitations. When N limited growth,
excess energy management may become important to decrease the risk of photoinhibition and oxidative stress; when the sink of electrons constituted by NO3-
reduction was not present, the cells tended to decrease their phycobiliprotein content, possibly in order to minimize the size of PSII antennas and decrease excitation. When
energy was limiting, the energy saved for N assimilation in NH4+-grown cells was invested in antenna pigments to allow for a higher energy input
Variations on the Author
No full text“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
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe 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
Larry O. Spencer, Conference Author Presentation
No full textGen. Larry O. Spencer, USAF (Ret.), author of Dark Horse: A Journey from the Horseshoe to the Pentago
Dispelling the Myths Behind First-author Citation Counts
No full textWe 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
On the polyphasic quenching kinetics of chlorophyll a fluorescence in algae after light pulses of variable length
No full textThis study reports on kinetics of the fluorescence decay in a suspension of the alga Scenedesmus quadricauda after actinic illumination. These are monitored as the variable fluorescence signal in the dark following light pulses of variable intensity and duration. The decay reflects the restoration of chlorophyll fluorescence quenching of the photosystem II (PSII) antennas and shows a polyphasic pattern which suggests the involvement of different processes. The overall quenching curve after a fluorescence-saturating pulse (SP) of 250-ms duration, commonly used in pulse amplitude modulation applications as the tool for estimating the maximal fluorescence (Fm), has been termed P–O, in which P and O have the same meaning as used in the OJIP induction curve in the light. Deconvolution of this signal shows at least three distinguishable exponential phases with reciprocal rate constants of the order of 10, 102, and 103 ms. The size of the long ([103 ms) and moderate (*102 ms) lasting components relative to the complete quenching signal after an SP increases with the duration of the actinic pulse concomitantly with an increase in the reciprocal rate constants of the fast (*10 ms) and moderate quenching phases. Fluorescence responses upon single turnover flashes of 30-ls duration (STFs) given at discrete times during the P– O quenching were used as tools for identifying the quencher involved in the P–O quenching phase preceding the STF excitation. Results are difficult to interpret in terms of a single-hit two-state trapping mechanism with distinguishable quenching properties of open and closed reaction centers only. They give support for an earlier hypothesis on a double-hit three-state trapping mechanism in which the so-called semi-closed reaction centers of PSII are considered. In these trapping-competent centers the single reduced acceptor pair [PheQA]1-, depending on the size of photoelectrochemically induced pH effects on the QBbinding site, functions as an efficient fluorescence quencher
Author Under Sail The Imagination of Jack London, 1902-1907
No full textIn this second volume of Author Under Sail Jay Williams investigates the life of Jack London as a professional writer at the turn of the 1900s, as his publications spanned The Call of the Wild to The Iron Heel and The Road. While documenting key life events, especially his rising fame, this biography explores London's necessity to illustrate the inner workings of his own vast imagination through his socialist essays and fiction.Cover -- Title Page -- Copyright Page -- Contents -- Acknowledgments -- Introduction -- 1. Howl, O Heav'nly Muse! -- 2. Jesus in the Theater of Socialism -- 3. Jack London's Place in American Literature -- 4. Theater of War, Theater at Home -- 5. Revolution, Evolution, and the Scene of Writing -- 6. The Jack London Show Goes on the Road -- 7. Red Atavisms and Revolution -- 8. Earthquake Apocalypse and Building the City, Boat, and House Beautiful -- 9. The Future of Socialism and the Death of the Individual -- 10. The Road Never Ends -- Notes -- Bibliography -- IndexIn this second volume of Author Under Sail Jay Williams investigates the life of Jack London as a professional writer at the turn of the 1900s, as his publications spanned The Call of the Wild to The Iron Heel and The Road. While documenting key life events, especially his rising fame, this biography explores London's necessity to illustrate the inner workings of his own vast imagination through his socialist essays and fiction.Description based on publisher supplied metadata and other sources.Electronic reproduction. Ann Arbor, Michigan : ProQuest Ebook Central, YYYY. Available via World Wide Web. Access may be limited to ProQuest Ebook Central affiliated libraries
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