1,720,956 research outputs found
Harnessing Cosmic Carbon: Anaerobic Microbial Responses to Fullerenes Under Early Earth Conditions
No full textFullerenes of extra-terrestrial origin may have been accessible as a carbon source for anaerobic microorganisms on the early Earth. Very little is known about how microorganisms respond to and utilise fullerenes and their soluble derivatives, particularly in anoxic environments. We present an investigation into the effects of fullerenes C60 and C70 and their hydroxylated fullerol derivatives on an environmentally relevant anaerobic community and a microbial isolate. Anaerobic microorganisms were cultured in microcosms with suspensions of fullerenes with and without supplementary carbon under different levels of light exposure. Relevant early Earth environmental conditions were simulated by irradiating fullerene suspensions with 254nm UV light for two weeks in the absence of oxygen and the accessibility of the photodegradation products was assessed. We find that the anaerobic community is capable of utilising C60 as a sole carbon source, but that C70 is inhibitory. Additionally, we find that both C60 and C70 fullerol are inhibitory to the anaerobes in this study, which is contradictory to previous studies conducted under aerobic conditions. The anaerobic isolate was unable to grow on C60 alone, but after UV exposure, the C60 photodegradation products served as a highly accessible carbon source. Thus, we present a report on the utilisation of photodegraded C60 as the sole carbon source by an anaerobic microorganism under anoxic conditions. Further data shows that fullerenes and their derivatives can both enhance and inhibit the growth of anaerobic microorganisms, which has important implications for their interactions with early life on Earth and their impact on anoxic environments as pollutants in the present day
Extra-terrestrial fullerenes as a food source for microorganisms on the early Earth
Get PDFThe search for extra-terrestrial life is an ever-evolving field of research that seeks to identify and understand life elsewhere in the universe. In order to narrow down this expansive search it is necessary to establish a set of parameters pertaining to habitability. It is therefore of significant interest for astrobiologists to study the conditions extra-terrestrial life may need to arise. Earth is the only planet currently known to host life and therefore provides an excellent model system as a case study for astrobiologists seeking to search for and understand life on distant planets. Very little is currently known about primitive terrestrial microorganisms, particularly with regard to their energetic processes and metabolism. It is well established that the origin of terrestrial life occurred simultaneously with the Late Heavy Bombardment, during which time a massive amount of organic-rich meteoritic material was accreted. This likely resulted in the accumulation of a large reservoir of extra-terrestrial carbon on the early Earth around the time primitive microorganisms were evolving more advanced metabolic processes. While it was previously assumed early life must have been purely autotrophic, the presence of potentially biologically accessible organics in the early Earth environment introduces the possibility that primitive microbes may have evolved to exploit these resources and develop early heterotrophic mechanisms much earlier than is currently postulated.
Fullerenes are found in abundance in carbonaceous chondrites and were therefore almost certainly present in relatively high amounts on the early Earth. Very little is known about the effect of fullerenes and their naturally occurring water-soluble derivatives, fullerols, on microorganisms, particularly in anoxic environments, and therefore very limited conclusions can be drawn for their potential effects on primitive microbes. Furthermore, the effects of the extreme early Earth environmental conditions, such as short-wave UV exposure, on the chemical properties of fullerenes and their derivatives are yet to be characterised; yet investigating this is critical in understanding how fullerenes may have fulfilled an important ecological niche.
In this thesis, I will explore the effect of fullerenes C60 and C70 and their fullerol derivatives on microorganisms and their potential as carbon sources for heterotrophic metabolism. An anaerobic community was studied as an analogue of a primitive microbial system, with an isolate derived from this community used for further, more comprehensive analyses of biological fullerene interactions. Furthermore, the effect of fullerenes and fullerols on select aerobic environmental isolates and model species E. coli was examined. With these microbiology studies, I show that fullerene response is highly species-specific and closely linked to the growth environment. It is demonstrated that fullerene C60, while inaccessible in its native form, can be converted to a highly accessible carbon source for anaerobic microorganisms when exposed to the high UV and anoxic conditions found on early Earth. To further understand the biodegradation pathways involved in C60 utilisation and the mechanism of toxicity to aerobic species, a comprehensive metabolomics study was carried out in which I present a novel set of results describing the innate biological effect of fullerenes on both an aerobic and anaerobic microorganism. The results presented in this thesis in their entirety give a clearer picture of how fullerenes on the early Earth and other habitable planets could provide primitive microbes with a previously undescribed source of carbon and energy
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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