1,720,959 research outputs found
N2O reduction in soils
Full text linkN2O is a known greenhouse gas that increased by 16% over the last 200 years. The main sources are native and agricultural soils where predominantly soil bacteria perform nitrification and denitrification with N2O as side and intermediate product, respectively. A complete denitrification, at which N2O is reduced to N2, is assumed to be the main elimination or sink process of N2O in the soils, beside dissolution in water. N2O sinks were first observed and measured in field studies. For a better understanding of the N2O sink processes laboratory studies with defined conditions were carried out, most of them under anaerobic conditions and airtight closed systems. We studied N2O sink processes in an experimental set up that had a continuous gas flow through soil samples to avoid a limitation of substrate gas concentrations over the experiment time. This set up allowed us to keep temperature and gas concentrations of N2O and O2 constant or selective to change them at discretion during the experiments. The concentrations of N2O and CO2 at the inlet and at the outlet of the incubation vessels could be measured continuously with a gas chromatograph. Therefore, we could determine the N2O consumption and the CO2 emission throughout the experiments. Our overall objective was to determine the ability and capacity of different soils to consume N2O at low oxygen concentrations and to determine the influence of certain parameters on N2O consumption and its rate. A change in the ratio of 15N to 14N as well as in the ratio of 18O to 16O in the N2O molecule was observed with coexistent raise of the N2O concentration in the atmosphere. This observation gives reason to believe that one of the N2O production or consumption processes might be the reason for the change in the fractionation factor. Our first objective was to check to what extend the N2O consumption could influence the isotopic signature in the remaining N2O molecules. Therefore, we determined the N2O reduction rate, the reduction rate constant and synchronously the isotopic signature of N and O in the remaining N2O that left the sample. We observed that with a decreasing reaction rate constant the fractionation factors for N and O increased and vice versa. We could as well determine the ratio of the stable isotopes N / O that lay mostly betweenandwith an average around 2.4, which is in agreement with other observations. We could conclude that the fractionation factors of the stable isotopes N and O depend on the N2O reduction rate constant and that the ratio of the enrichment factors for the stable isotopes N and O is constant. This ratio can help to detect N2O consumption if reduction is the dominating process in the turnover of N2O. The predominant faith of N2O in soils is either the emission to the atmosphere, the dissimilatory reduction to N2 or the dissolution in water. However, other types of N2O sink were observed, for example N2O fixation with following transforming to NH3. Hence, our second objective was to test, if these observations and a possible incorporation of N-N2O into soil organic matter are of ecological relevance in soils. We approached this problem by using labelled 15N2O as the only nitrogen source for four different soils over several days in our flow through set-up. We measured N2O consumption continuously and δ15N of soil organic matter before and after the experiment. The results revealed an average of the 15N enrichment in the soil organic matter of about 0.019%. Therefore, we could conclude that assimilatory reduction of N2O plays a negligible role as a N2O sink in soils, at least for our tested soils.
Although denitrification and therefore N2O consumption is known to occur under anaerobic conditions there are observations of N2O consumption at low O2 or aerobic conditions. This could indicate that N2O consumption is a more widespread and important process in soil as assumed. Our third objective of this thesis was to study the ecological relevance of N2O consumption in view of the total respiration in soils. Thereby, N2O and total respiration rates and the Michaelis-Menten Constant (km) values for N2O consumption were determined at different temperatures and oxygen concentrations. The received km values were between 1.8 – 10.4 ppm in soil gas phase (0.045 – 0.26 μM in soil solution) at all applied temperature and oxygen concentrations. This range fits with km values of other observations and suggests that there might be a common range of km values for N2O consumption in soils. In contrast, the km values determined for pure cultures of N2O reducing bacteria were about 9 times larger (2.4 – 7.5 μM in soil solution, converted: 96 -300 ppm). This result might point to a higher affinity of the N2O reducing enzyme in soils than in pure cultures. The ratio of N2O to total respiration gave us the amount of electrons that were transmitted to a N2O molecule instead to O2. This was for our soils up to 1.25%. Our observations showed that N2O and aerobic respiration could occur simultaneously probably in different microhabitats within the soil.
Only 1% of the microbes in soils have the ability to produce the enzyme N2O reductase that reduces N2O to N2. The production of the enzyme is controlled by environmental influences like oxygen concentration and the concentration of the denitrification intermediate products. Our objective for this part was to find out to what extent N2O treatments could influence the microbial community and the N2O reducing bacteria. We used two different DNA fingerprinting methods, RISA (ribosomal RNA intergenic spacer region analysis) and DGGE (denaturation gradient gel electrophorese) on four different soils, which showed N2O consumption. Through this method, we could conclude that all tested soils have strong differences in their microbial community. The treatment of the soils caused a shift in the microbial community, but it was not clear which of the parameter the high temperature, low oxygen, and/or high N2O concentration, had the most effect on the microbial community.
We could prove that all soils we tested have the ability to reduce N2O to N2 at low oxygen concentrations. The potential of this process depends highly on the N2O and O2 concentrations, temperature, and aggregate sizes in the soil. Altogether, we enhanced our knowledge about the N2O consumption process and could conclude that this process is of ecological importance in soils
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
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
Author Under Sail The Imagination of Jack London, 1893-1902
No full textIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Intro -- Title Page -- Copyright Page -- Dedication -- Contents -- Acknowledgments -- Introduction -- 1. Spirit Truth -- 2. From Absorption to Theatricality and Back Again -- 3. "I Will Build a New Present" -- 4. Sons as Authors -- 5. Fathers as Publishers -- 6. The Daughter as Author -- 7. Lovers as Authors -- 8. At Sea with the Family -- 9. Yellow News, Yellow Stories -- 10. The Return Home -- Notes -- Bibliography -- Index -- About Jay WilliamsIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Description based on publisher supplied metadata and other sources.Electronic reproduction. Ann Arbor, Michigan : ProQuest Ebook Central, YYYY. Available via World Wide Web. Access may be limited to ProQuest Ebook Central affiliated libraries
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