1,720,998 research outputs found
Spatial variability of N2O concentrations and of denitrification-related factors in the surficial groundwater of a catchment in Northern Germany
No full textN2O concentrations and denitrification- related factors (NO3, SO4, dissolved organic carbon (DOC) and CO2) were investigated in the surface groundwater of a catchment in northern Germany, the Fuhrberger Feld Aquifer (FFA). We sampled 79 plots that were selected according to the three criteria of land use, historical land use conversion (1954-1995) and groundwater level. We sampled three sites within each plot. The sampling depth was 0.5 m below the groundwater surface. We found no indication for the occurrence of autotrophic denitrification in the surface groundwater. Heterotrophic denitrification was identified as the main process for N2O accumulation. The variability of N2O concentrations on the plot-scale was extremely high and was poorly explained by the three sampling criteria. Other denitrification-related variables such as NO3, SO4 and DOC were less variable. The selection criteria land use and groundwater level clearly influenced the order of magnitude of N2O concentrations in the surface groundwater. Under arable land, high NO3 concentrations resulted in high N2O concentrations. The surface groundwater under forest and pasture was almost NO3 free and had also very small N2O concentrations. Plots where the distance from the soil surface to the groundwater surface was large (>1 m up to 3.4 m) showed higher N2O concentrations in the surface groundwater than plots where the distance was small (<1 m). A larger distance from the soil surface to the groundwater leads to a longer residence time and more decomposition of DOC in the soil. Consequently the less bioavailable DOC could inhibit the efficiency of the heterotrophic denitrification in the groundwater, yielding more N2O. Elevated organic carbon levels in plots with historic land use conversion (pasture to arable) were very stable and did not influence N2O concentrations. The high within plot variability showed that an upscaling of N2O from the plot-scale to the catchment-scale is possible as long as the groundwater Level regime and the land use do not change. (C) 2008 Elsevier B.V. All rights reserved.German Research Foundation (DFG
The dynamics of N(2)O near the groundwater table and the transfer of N(2)O into the unsaturated zone: A case study from a sandy aquifer in Germany
No full textThe research area was the Fuhrberger Feld aquifer (FFA) in northern Germany. It is situated about 30km northeast of the city of Hannover and covers about 300km(2). Six multilevel sampling wells along a representative strip under predominantly arable land along a groundwater flow-line were sampled from the groundwater table down to a depth of 10m below the soil surface. We measured N(2)O, CO(2), NO(3)(-), SO(4)(2-), DOC, pH, redox potentials and O(2) concentrations. N(2)O accumulated at four out of six wells close to the groundwater table. About 20% of N(2)O that occurred between the groundwater table and 7-8m below it resided in the top 0.4m. An exchange zone for N(2)O at the interface between the saturated and the unsaturated zone extended 0.55 +/- 0.22m below the groundwater table and acted as a source and sink for N(2)O. N(2)O below the exchange zone cannot be transferred from the groundwater to the atmosphere. The upward fluxes from the exchange zone into the unsaturated zone at the six wells ranged between 0.0009 and 0.3kg N(2)O ha(-1) year(-1). The yearly downward fluxes into the exchange zones had about the same order of magnitude as the upward fluxes. The upward and downward fluxes of N(2)O at the (fluctuating) water table did cancel out each other, but this does not yet imply, that the N(2)O fluxes at the soil surface also cancel out each other. N(2)O-N:NO(3)-N ratios were highly variable ranging from 0.0002 to 0.0417. A multiple regression for the monthly N(2)O amounts in the exchange zone could explain 66% of the yearly variation. The significant variables were NO(3)(-), CO(2), pH, and O(2). Therefore, a combination of the land use (NO(3)(-)), the geochemical boundary conditions (pH) and the type of denitrification reaction (O(2) and CO(2) indicate the importance of a heterotrophic denitrification process) governed the N(2)O dynamics in the surface groundwater of the FFA and its transfer into the unsaturated zone. (C) 2007 Published by Elsevier B.V
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
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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