1,720,963 research outputs found
Water temperature, salinity, DOC content and THNS concentration in samples taken during POLARSTERN cruise to the Fram Strait and Greenland Sea
No full textDissolved organic matter (DOM) was isolated with XAD-2 and 4 resins from different water masses of the Greenland Sea and Fram Strait. The contribution of XAD-extractable dissolved organic carbon (DOC), operationally defined as 'recalcitrant' or humic substances, to total DOC was in the range of 45 ± 9% in surface waters and 60 ± 6% in deep waters. The carbohydrate concentration and composition were determined using the l-tryptophan/sulfuric acid method (for the bulk carbohydrate concentration, TCHO) and high performance anion-exchange chromatography after sulfuric acid hydrolysis (for the distribution of total hydrolysable neutral sugars, THNS). Carbohydrates contributed up to 6.8% to both total and recalcitrant DOC. TCHO contribution to total DOC decreased with depth from on average 4.1 ± 1.2% in surface waters to 2.2 ± 1.0% in deep waters, whereas the THNS contribution was similar in both layers, accounting for 2.5 ± 1.6% (surface) and 2.4 ± 0.2% (at depth). TCHO contribution to XAD-extractable DOC also decreased with depth from 4.5 ± 1.7% to 2.1 ± 1.0%, whereas THNS contribution was almost constant, with yields of 0.5 ± 0.3% for surface samples and 0.6 ± 0.1% at depth. The molecular size distribution of the recalcitrant DOM showed for all fractions a clear trend towards small molecules in the deep sea. More than half of the XAD-extractable carbohydrates of surface samples and more than 70% of deep sea samples were found in the nonpolar fraction from XAD, which was eluted with methanol. Glucose was the dominant carbohydrate in the surface water samples, whereas in the deep sea the composition was more uniform. In the XAD extracts, the compositions were less variable than in the original samples. The neutral sugar composition, in particular glucose and the deoxysugars, is indicative of the diagenetic state of the extracted DOM. The molar ratio (fucose + rhamnose)/(arabinose + xylose) was lowest for deep sea extractable DOM, indicating a high contribution of material modified by microorganisms. The THNS composition and distribution reveal that “recalcitrant” carbohydrates are heteropolysaccharides, carbohydrate units incorporated into a framework of a highly nonpolar structure with a lack of functional groups
(Table 1) Temperature, salinity and dissolved organic carbon during POLARSTERN cruise ARK-XIII/3
No full text(Table 1) Temperature, salinity and dissolved organic carbon during POLARSTERN cruise ARK-XIII/
(Table 2) Composition and concentration of total hydrolyzable neutral sugars in samples taken during POLARSTERN cruise ARK-XIII/3
No full text(Table 2) Composition and concentration of total hydrolyzable neutral sugars in samples taken during POLARSTERN cruise ARK-XIII/
Biogeochemie gelöster Kohlenhydrate in der Arktis
No full textA detailed characterization of dissolved carbohydrates in the Siberian rivers and shelf areas, the Kara and Laptev Seas, the central Arctic Ocean, Fram Strait, and Greenland Sea is presented. Highest concentrations of total carbohydrates (25 mM C on average) were measured in the samples of the Russian rivers. A strong decrease of the concentrations occurred during the transition into the marine environment (5.3 mM C on average). In deep waters, the total carbohydrate concentrations were below 2 mM C. The main component of dissolved carbohydrates was glucose, which was well suited for the characterization of the diagenetic state of DOM. Terrigenous and diagenetic old marine DOM had very low glucose proportions between 20 and 28% of total carbohydrates. In contrast, freshly produced DOM was characterized by high glucose proportions of up to 86%. Indicators for diagenetic modifications were also fucose, rhamnose, and arabinose, whose proportions increased with increasing diagenetic degree to approx. 40%. The composition of refractory carbohydrates was determined by extraction of recalcitrant organic matter from the seawater using a combination of XAD-2 and -4 adsorption resins. With increasing age of DOM, the proportion of the humic substances of the total DOC and of the total carbohydrates increased from 45% in surface samples to 67% in the deep sea. Part of refractory carbohydrates may be composed of chemically modified carbohydrates, which are not accessible with the chromatographic method. More than the half of the XAD-extractable sugars of surface samples and more than 70% of deep sea samples were found in the unpolar fraction. It was concluded that the majority of refractory carbohydrates were bound or associated to unpolar compounds of small molecular size. Using the ratio of the sum of the molar proportions of the deoxysugars and the sum of arabinose and xylose, the extracted humic substances were characterized with respect to their diagenetic degree
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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