1,721,003 research outputs found
Dissolved organic carbon in seepage water - Production and transformation during soil passage
No full textDissolved organic carbon (DOC) in seepage water can combine with organic pollutants, with Al and heavy metal ions and transport them through the soil profile with a potential to contaminate groundwater. We studied the production of DOC in aerobic decomposition experiments at 8 degrees C and moisture close to field capacity in soils from two sites with different microbial activities (spodic dystric Cambisols with moder (SLB) and mor-moder (SLS) layers) using C-13-depleted plants of differing decomposability (Epilobium angustifolium and Calamagrostis epigeios). Additionally, we investigated the DOC transformation during soil passage in decomposition experiments and in the field for the sites SLB and SLS. For SLS, decomposition of Epilobium resulted in a cumulative CO2 production of 14% of the added C within 128 days. Priming effects were negligible. CO2: production for the experiments using Calamagrostis was less with 11% for SLB and 10% for SLS. Cumulative DOC production was markedly high in the Epilobium decomposition experiment, being 25 g m(-2), out of which 11 g m(-2) were Epilobium-derived (2% of the added C). For the Calamagrostis experiments, cumulative productions of DOC and Calamagrostis-derived DOC (0.1% of the added C for SLS and SLB) were much less. During the soil passage, much of the DOC was removed by sorption or decomposition processes. Field studies at SLS and SLB using C-13 natural abundance showed that C-13 distribution of soil organic matter increased with depth, probably mainly due to a discrimination of C isotopes by decomposing microorganisms. DOG, however, showed a depletion of C-13 from -28 parts per thousand PDB to -29 parts per thousand (SLB at 40 cm) or --28 to -30 parts per thousand (SLS at 20 cm) with depth, owing to preferential decomposition of C-13-enriched substances or preferential adsorption. This study indicates that DOC production is strongly affected by litter composition and that significant changes in DOC composition may occur during its passage through a soil depth of 40 cm
C-13 and N-15 distributions in three spodic dystric cambisols under beech and spruce
No full textThe study of natural isotopic abundance signatures is useful to gain further insights in the processes resulting in depthwise changes in the composition of soil organic matter (SOM). Objectives were to describe the delta(13)C and delta(15)N abundances of SOM with depth in soils from a 153-year old beech (B1), a 119-year old spruce (F1) and a 61-year old spruce (F2) stand at Selling, north-west Germany, and to study, how podzolisation affects the isotopic abundances of C-13 and N-15 in the SOM. The degree of podzolisation decreased in the order F1 > B1 > F2. At the surface of the humus layer of all three sites, delta(13)C values are approximately 1 to 4 parts per thousand higher than in the leaves and needles, probably mainly due to the discrimination of C-13 by microbial decomposition. C-13 abundances in the organic layers of Fl and F2 increased only slightly from -27.6 parts per thousand PDB (B1, L) to -27.2 parts per thousand PDB (B1, Oh) and from -26.3 parts per thousand PDB (F2, L) to -25.9 parts per thousand PDB (F2, Oh), suggesting that biotic activity resulted in mixing of organic matter. At Fl, however, C-13 abundance increased from -27.5 parts per thousand PDB (L) to -26.0 parts per thousand PDB (Oh) which reflects the lack of mixing by animals. In the upper 2-4 cm of the mineral soil, i.e., in the eluvial horizons Aeh, C-13 values showed a minimum at the spruce sites which was presumably related to a translocation of C-13 enriched fulvic acids. Depthwise changes in delta(15)N values were not related to podzolisation processes. At all three sites, a N-15 enrichment with depth occurred in the mineral soil which is the result of the discrimination of N-15 by microbial decomposition
The origin of soil organic C, dissolved organic C and respiration in a long-term maize experiment in Halle, germany, determined by C-13 natural abundance
No full textFor a quantitative analysis of SOC dynamics it is necessary to trace the origins of the soil organic compounds and the pathways of their transformations. We used the C-13 isotope to determine the incorporation of maize residues into the soil organic carbon (SOC), to trace the origin of the dissolved organic carbon (DOC), and to quantify the fraction of the maize C in the soil respiration. The maize-derived SOC was quantified in soil samples collected to a depth of 65 cm from two plots, one 'continuous maize' and the other 'continuous rye' (reference site) from the long-term field experiment 'Ewiger Roggen' in Halle. This field trial was established in 1878 and was partly changed to a continuous maize cropping system in 1961. Production rates and delta(13)C of DOC and CO2 were determined for the Ap horizon in incubation experiments with undisturbed soil columns. After 37 years of continuous maize cropping, 15% of the total SOC in the topsoil originated from maize C. The fraction of the maize-derived C below the ploughed horizon was only 5 to 3%. The total amount of maize C stored in the profile was 9080 kg ha(-1) which was equal to about 31% of the estimated total C input via maize residues (roots and stubble). Total leaching of DOC during the incubation period of 16 weeks was 1.1 g m(-2) and one third of the DOC derived from maize C. The specific DOC production rate from the maize-derived SOC was 2.5 times higher than that from the older humus formed by Cg plants. The total CO2-C emission for 16 weeks was 18 g m(-)2. Fifty-eight percent of the soil respiration originated from maize C. The specific CO2 formation from maize-derived SOC was 8 times higher than that from the older SOC formed by C-3 plants. The ratio of DOC production to CO2-C production was three times smaller for the young, maize-derived SC than for the older humus formed by C-3 plants
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
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
- …
