1,721,033 research outputs found
Microbial nitrogen metabolisms and nitrogen recycling through DNRA in low-oxygen marine waters
No full textMicroorganisms regulate global nitrogen (N) availability by conducting complex series of metabolisms that transform N compounds and can produce bio-unavailable forms of N (N-loss).
N-loss primarily occurs in the absence or near-absence of oxygen (O₂), and thus O₂ emerges as an important regulator of N availability. Low-O₂ pelagic marine environments are among the largest venues for N-loss and they are currently expanding as a result of ocean deoxygenation, driven by
climate change. These changes have potential to alter N availability in the ocean and create feedbacks on climate, but the outcomes are difficult to predict, partly because microbial N metabolisms are complex. Three different N metabolisms can occur under low-O₂ conditions: two metabolisms (denitrification, anammox) result in N loss, but another (DNRA) recycles N in the environment. We know relatively less about DNRA and the ways O₂ can influence N loss and recycling. In this thesis I conduct experiments in a model low-O₂ marine environment to create
new knowledge about N-recycling and the ways microbial N metabolisms respond to changing O₂. In chapter 2, I test for metabolisms that can consume N₂O across a range of O₂ conditions to
determine whether N₂O is lost through denitrification or recycled. I find that N₂O cannot be recycled, but N₂O-loss can still be active in the presence of low O₂. In chapter 3, I test the
importance of DNRA in marine waters and generate new information about microorganisms that conduct DNRA. I find that DNRA is highly variable and can be the dominant metabolism, overall.
I also find that DNRA is conducted by facultatively aerobic organisms and is most active in intermittently-oxygenated environments. In the fourth chapter I test whether low O₂ can directly
regulate N loss and recycling. I find that O₂ can regulate all three metabolisms and potentially stimulate denitrification and DNRA. The observations that DNRA can be the dominant metabolism in pelagic marine environments and that O₂ can stimulate N metabolisms are two novel
findings that, if widely applicable, could alter models and forecasts for deoxygenation. I suggest future work to test extensibility and build on these results.Science, Faculty ofMicrobiology and Immunology, Department ofGraduat
Chromium isotopes : fractionation from continental weathering through to deposition in marine sediments
No full textVariation in the composition of chromium (Cr) stable isotopes has emerged as a powerful tracer for environmental processes as a result of the Cr isotope fractionation induced during the reduction of Cr(VI) to Cr(III). Comprehensive characterization of the geochemical processes that act on and can change Cr speciation, and of all processes that result in Cr isotope fractionation, is needed in order to make robust inferences based on the variation in Cr isotopic compositions. Our knowledge of Cr geochemistry in the natural environment is limited, with lab-based experiments often not capturing the natural complexity of the environment, in part due to Cr speciation being driven by kinetic factors, resulting in disequilibrium, as well as limited speciation data, partially due to a lack of reproducible methods. This dissertation presents a new speciation method and a wealth of new Cr speciation data resulting from the application of this method, including the first species-specific Cr isotope compositions measured in seawater across an oxic-anoxic boundary. These results provide clear evidence of positive and negative excursions in water column δ53Cr(III) in response to oxygenation and deoxygenation events, respectively, which are likely to be reflected in the authigenic Cr sedimentary record. Modeling of water column data also highlights the role of reservoir effects in muting Cr isotope fractionation relative to the intrinsic fractionation factor associated with a given process, like Cr(VI) reduction. We find non-redox processes such as water mass mixing to be a key process in Saanich Inlet, while in treated stream waters we find evidence of substantial oxidative remobilization of Cr(VI) due to reaction between reactive Cr(III) precipitates and manganese (Mn) oxides. Together, the work in this dissertation identifies the local key processes controlling Cr speciation and isotopic composition in these studied environments, with water mass mixing and in-situ Cr(III) oxidation in particular having a strong effect on the resulting Cr isotope composition, both of which are underrepresented processes in current studies. By contributing this new knowledge on Cr behaviour in the modern environment, we help to facilitate more robust inferences of Cr cycling in past environments.Science, Faculty ofEarth, Ocean and Atmospheric Sciences, Department ofGraduat
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
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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