1,721,019 research outputs found
High rates of denitrification and nitrous oxide emission in arid biological soil crusts from the Sultanate of Oman
No full textUsing a combination of process rate determination, microsensor profiling and molecular techniques, we demonstrated that denitrification, and not anaerobic ammonium oxidation (anammox), is the major nitrogen loss process in biological soil crusts from Oman. Potential denitrification rates were 584±101 and 58±20??mol N?m?2?h?1 for cyanobacterial and lichen crust, respectively. Complete denitrification to N2 was further confirmed by an 15NO3? tracer experiment with intact crust pieces that proceeded at rates of 103±19 and 27±8??mol N?m?2?h?1 for cyanobacterial and lichen crust, respectively. Strikingly, N2O gas was emitted at very high potential rates of 387±143 and 31±6??mol N?m?2?h?1 from the cyanobacterial and lichen crust, respectively, with N2O accounting for 53–66% of the total emission of nitrogenous gases. Microsensor measurements revealed that N2O was produced in the anoxic layer and thus apparently originated from incomplete denitrification. Using quantitative PCR, denitrification genes were detected in both the crusts and were expressed either in comparable (nirS) or slightly higher (narG) numbers in the cyanobacterial crusts. Although 99% of the nirS sequences in the cyanobacterial crust were affiliated to an uncultured denitrifying bacterium, 94% of these sequences were most closely affiliated to Paracoccus denitrificans in the lichen crust. Sequences of nosZ gene formed a distinct cluster that did not branch with known denitrifying bacteria. Our results demonstrate that nitrogen loss via denitrification is a dominant process in crusts from Oman, which leads to N2O gas emission and potentially reduces desert soil fertility
Degradation of diatom-derived dissolved organic matter (DOM) in surface seawater
No full textStored surface seawater originally collected in the North Sea was amended with dissolved organic matter (DOM) obtained from the diatom Skeletonema marinoi by exposing the diatom culture to a hydrostatic pressure level of 40 MPa for 24 h. To this end, S. marinoi had been grown to stationary phase in L1 medium plus silicate (Guillard & Hargraves 1993) at 15°C under a light/dark regime of 14/10 h. Diatom-cell-free DOM was added to aliquoted seawater samples at initial concentrations of 250 µmol C/L. The microbial degradation of the added DOM and the microbial response to DOM-amendment at 15°C and in darkness was followed for 2 weeks. The seawater was subsampled at defined time intervals to analyze a number of variables
Pressure-induced leakage of dissolved organic matter (DOM) from diatom-bacteria aggregates
No full textModel diatom aggregates were produced from the diatom Skeletonema marinoi and the natural microbial community of seawater collected in Oeresund (Stief et al. 2023), Central Arctic Ocean, and Japan Trench. S. marinoi was grown to stationary phase in L1 medium plus silicate (Guillard & Hargraves 1993) at 15°C under a light/dark regime of 14/10 h. The diatom aggregates were individually incubated at either atmospheric pressure (0.1 MPa = control treatment) or at gradually increasing hydrostatic pressure (0.1-100 MPa = pressure treatment) throughout 20 days in darkness and at 3°C. The pressure treatment simulated the sinking of diatom-bacteria aggregates from the ocean surface down into a hadal trench of 10 km depth. Pressure-induced leakage of dissolved organic matter (DOM) was followed throughout the incubations. Ambient concentrations of different DOM components were measured: Dissolved organic carbon (DOC), total dissolved nitrogen (TDN), protein-like and humic-like DOM fluorescence
Pressure-induced leakage of dissolved organic matter (DOM) from different diatom species
No full textFour diatom strains obtained from different culture collections were grown to stationary phase in L1 medium plus silicate (Guillard & Hargraves 1993) at 15°C under a light/dark regime of 14/10 h. For experimentation, the diatom strains were incubated at either atmospheric pressure (0.1 MPa = control treatment) or at gradually increasing hydrostatic pressure (0.1-100 MPa = pressure treatment) throughout 21 days in darkness and at 3°C. The pressure treatment simulated the sinking of particle-associated diatoms from the ocean surface down into a hadal trench of 10 km depth. Pressure-induced leakage of dissolved organic matter (DOM) was followed throughout the incubations. Both ambient concentrations and intracellular concentrations of different DOM components were measured: Dissolved organic carbon (DOC), total dissolved nitrogen (TDN), protein-like and humic-like DOM fluorescence, total proteins, total polysaccharides, laminarin, and dimethylsulfoniopropionate (DMSP). The cell abundance of the different diatom strains was followed throughout the incubations
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
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