1,720,965 research outputs found
Quantitative relationship among phytoplankton body size classes and production processes in the North Adriatic Frontal region
No full textSeasonal characteristics of size-fractionated phytoplankton community and fate of photosynthesized carbon in a sub-antarctic area (Straits of Magellan)
No full textPhytoplankton community size drives the rates of biogenic carbon and the overall structure and dynamics of the marine pelagic food web. The Straits of Magellan, an inland passage between the Pacific and Atlantic Oceans, can be separated in three main sub-basin: the western-Pacific, the V-shaped central zone, and the eastern-Atlantic. To provide insights on the food structure of the phytoplankton community, size-fractionated chlorophyll a concentration and primary production rates were measured across the three sectors of the Magellan Straits in four periods between 1989 and 1995 in the Straits. Phytoplanktonic biomass and production ratios provided ecological insights on the food web structure, including the relevance of grazing on its largest fraction.
The micro-phytoplanktonic fraction (>10 μm) in the western-Pacific sub-basin is significantly less abundant than in the Central and Atlantic ones. Conversely, the lowest abundance of the pico- fraction (< 2.0 μm) is encountered in the Atlantic sub-basin. The observed patterns agree with the diffusion of smaller-size fractions from the western towards the easternmost sector of the Straits, and suggest that the largest phytoplankton tend to accumulate in the inner stretch of the Straits, being constrained by a clockwise gyre generated by tidal phases or partialy spilling out into the Atlantic sector. The most active grazing activities occur in the central arm during the spring bloom and last even in summer.
Our results pinpoint also that the basic levels of the planktonic food web rely on the nano-phytoplankton (10-2 μm) fraction, which is the main contributor to the continuum multivorous food web. When nutrient pulses from land freshwater and water mixing enter the system, the structure of the plankton in the Straits shifts towards the herbivorous food web and is characterized by the presence of large-size diatoms. The complex dynamics of the plankton comuunities in the Straits keep it in a persistent mesotrophic state, featuring a lower trophic status of than the Antarctic coastal waters but a much higher one than oligotrophic temperate areas
Penetration of solar radiation into waters of Messina Strait (Italy)
No full textThe optical properties of the waters of five different stations, three located in the Messina Strait and two near the Strait (open sea), were analysed. Direct spectral measurements of the downward solar irradiance (290 - 800 nm) at different depths (0.5 m, 7 m, 10 m, 13 m, 20 m) were made using a cosine sensor connected to a spectroradiometer. Water samples were collected in the surface layer and their absorption spectra were analysed. The natural fluorescence profiles, along the water column, were determined using a fluorometer (SBE 911 plus - Sea Teach). The spectral attenuation coefficient (K-lambda), the variation of K-lambda in different wavelength ranges (Delta K-Delta lambda), the wavelength corresponding to minimum value of K-lambda, the spectral depths of penetration of both 1% and 10% of the sub-surface irradiance values (P-lambda), the depths of 1% of penetration of UVB, UVA and PAR, the depth ranges of the maxim concentration of Chl a and superficial CDOM were measured at each station. The maximum solar UVB penetration was about 65% of the photic zone and the maximum UVA penetration was nearly 100% (data of the Ionic sea station). Thus, a large part of the photic zone was exposed to UV radiation sufficient to cause a possible reduction in the photosynthetic activity of phytoplankton. The spectral penetration of solar radiation, especially UVB radiation, was significantly different in the three stations of the Strait with respect to the two stations studied in the open sea. This shows that variations in the spectral attenuation along the water column can be used as an indicator of properties of the water body
Distribution of the prokaryotic biomass and community respiration in the main water masses of the Southern Tyrrhenian Sea (June and December 2005)
No full textThe distribution of the prokaryotic biomass (from both abundance and cell volume measurements) and microbial community respiration (by ETS activity) in the main water masses of the Southern Tyrrhenian Sea were studied. The data were collected from surface to the bottom depth (max 3600 m) in July and December 2005. Prokaryotic abundance and microbial respiration were higher in summer than late-autumn and decreased with depth in accordance with the water masses. The opposite was found for the prokaryotic cell volumes that increased with depth and were higher in December. The cell carbon content varied within the water masses and study periods (range 9–34 fgCcell 1) and overestimations and underestimations of biomass there would have been by using the routinely adopted conversion factor (20 fgCcell 1). The depth-integrated respiratory rates resulted comparable in the photic and aphotic layers. In July, 210 and 225mgCm 2 day 1 in the euphotic and aphotic zones, respectively, were remineralized while in December, 112 and 134mgCm 2 day 1, respectively, were. Speculations to quantify the carbon flow mediated by microbial community suggested the occurrence of different microbial behavior within the different water masses
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
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