1,720,956 research outputs found
Iron cycling and metal utilization by phototrophic and diazotrophic bacteria in iron-rich aquatic systems
Get PDFBackground. The availability of bioessential metals influenced the evolutionary trajectory and activity of life on early Earth. Bacteria utilize trace metals such as Mo in biological nitrogen fixation, which supports the productivity of the entire biosphere. Bacteria transform Fe between different valence states with the conservation of energy, all the while transforming Fe between dissolved and mineral forms. These biological processes were carried out by the early microbial biosphere as early as the Archean Eon and are still carried out by microbes today. Although the Earth today has drastically different atmospheric and aquatic chemical conditions than the early Earth, investigating these ancient microbial processes can help decipher their role in modern phenomena such as contaminant degradation and maintaining water quality. When we can contextualize these microbial reactions in a modern system that simulates a past environment, i.e., an analog, we can also deduce how early metabolisms were regulated by and influenced the chemistry of early Earth environments.
Aims. To investigate how molybdenum and iron availability influence key microbial processes in both iron and nitrogen cycles using modern organisms and ecosystems that are analogs to early Earth. Three studies specifically (1) investigate the role that photosynthetic iron oxidation plays in the generation of reactive iron minerals that may degrade organic contaminants; (2) determine the sources of iron to a terrestrial aquatic system and how iron cycling organisms influence iron mineral formation; and (3) explore whether low Mo availability in an iron-rich Archean analog lake limits biological nitrogen fixation.
Methods. These studies used microbial and environmental sampling to document biogeochemical and biological trends. Specifically, anoxic culturing, physiological experiments, and high-performance liquid chromatography determined the metabolic capacities of Fe-cycling bacteria and metals of minerals in 2,4-D degradation. 16S rRNA amplicon sequencing assessed the abundance of microbes within mineralized creek samples, and hydrological approaches provided the context for the formation of iron mineralization. Scanning and transmission electron microscopy provided an in-depth view of the mineralogy of iron, while chemical extractions and assays quantified the forms of iron and informed its source. In iron-rich Deming Lake, environmental sensors and laboratory analysis provided context on the distribution of oxygen, nutrients, and metals within the lake. Isotope tracer studies and metagenomics/transcriptomics were used to indicate the major organisms involved in nitrogen fixation and the strategies they use to overcome low Mo availability.
Results. The increasing use of 2,4-D in agriculture raises concerns about its persistence in surface and groundwater and the environmental repercussions on ecosystems. Microbial degradation of 2,4-D is poorly understood under anoxic conditions, and we highlight this limitation as it relates to the metabolic functions of microorganisms and potential abiotic degradation in iron-rich conditions. Agricultural Fe-rich aquatic systems could play an underrecognized role in herbicide degradation and other biogeochemical element transformations due to microbial iron cycling. Clear Creek on the Iowa State University Campus has visible iron mineralization linked to episodic shallow groundwater discharge bearing Fe(II). The microbial community comprised putative iron-oxidizing and reducing organisms that likely influence the timing and type of these mineralization patterns. Fe-rich Deming Lake, MN is a chemical and biological analog for Archean oceans. Nitrogen fixation in the upper water column is dominated by Cyanobacteria despite Mo concentrations lower than predicted Archean concentrations. Despite this, nitrogen fixation is not Mo limited and alternative nitrogenases using Fe or V instead of Mo are not expressed. Mo-requiring nitrogenase likely relies on high-affinity Mo transport system and other ABC transporter cassettes necessary for transporting oxyanions, including Mo, into the cell.
Conclusions. Collectively, these findings enhance our understanding of the ecological roles of biogeochemical cycles in Fe-rich systems across Earth’s history, with implications in nutrient redox cycling and contamination mitigation. Moreover, it demonstrates the critical roles of trace metals, Fe and Mo, in shaping microbial metabolisms that have persisted through time. Further studies need to investigate the genetic basis of anaerobes in anoxic herbicide degradation, particularly when iron is present. Bacteria found in Clear Creek contribute to the formation of iron mineralization at sites of groundwater discharge, emphasizing the ecological diversity of agricultural watersheds and their potential to be hot spots for nutrient and element cycling. Deming Lake results suggest early diazotrophs could have sustained nitrogen fixation under Mo-limited conditions, shedding light on the adaptability of the nitrogenase enzyme and Mo-uptake systems in low-sulfate systems. Moreover, these results help resolve the paradox of the ancestral Mo nitrogenase utilization in the mid-Archean seen in phylogenetic studies and bulk δ15N isotope values found in Archean sediments
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
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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