1,721,265 research outputs found
Challenging bio- and eco-coronas in marine nano-ecotoxicology
No full textIn meeting the challenges associated with the study of nano-sized objects, a major area of research is
represented by the interaction of nanoparticles (NPs) with biological systems. Owing to their
characteristics, NPs interact in a fundamentally different fashion with biological entities than
molecular species. When in contact with biological fluids, the particle surface is covered by a layer
of adsorbed proteins and other biomolecules, in dynamic equilibrium with the surrounding
environment, termed the “biomolecular corona”, which provide the as-synthesized particle with a
unique biological identity. While within the field of nanotoxicology the importance of the study of
the biomolecular corona has been largely recognized as key to untangle the complicate interactions
of NPs with cells, environmental toxicology has just begun to consider the study of coronas in facing
the upcoming issue of NP pollution of the marine ecosystems. The main aim of this PhD was to
investigate the interactions of NPs with biomolecules in the marine environment in order to
understand their ecotoxicological implications. As a proxy of the emerging issue of plastic
contamination of marine ecosystems, polystyrene nanoparticles, with positive and negative surface
charges, were employed throughout the study. Firstly, the nanoparticles interactions with the sea
urchin Paracentrotus lividus, as a model invertebrate species, were considered. The biological
identity of positive and negative polystyrene nanoparticles entails the potential to promote particlecell
association, by assisting their interaction with the highly specialized immune systems of P.
lividus. Both positive and negative particles maintained hydrodynamic sizes indicative of a narrow
size distributions, mostly encompassing protein coated monomers and dimers, acquiring a net
negative surface charge. The observed corona-derived colloidal stability over time suggests that,
irrespectively of initial surface charge, in the biological milieu polystyrene nanoparticles can acquire
the same physical-chemical characteristics, possibly being presented for bio-nano interactions in a
comparable manner. The role of an adsorbed protein in promoting the association of positivelycharged
polystyrene nanoparticles was proven to lead to toxic effects sustained by the phagocytic
immune cells of the sea urchin, confirming that biomolecular coronas dictate the biological fate of
nanoparticles in marine invertebrate species, with a mode of action comparable to what established
in “classical” nanotoxicology. The subsequent studies focused on polystyrene NPs in marine waters,
as a primary target of their release in the environment. In such abiotic, yet biomolecule rich,
environment the interaction with extracellular polymeric substances (EPS) extruded by ubiquitous
photoautotrophic planktonic species (e.g. diatoms and cyanobacteria) determine the particle fate. The formation of an “eco-corona” reverses the typical colloidal behavior of positive and negative
polystyrene NPs, as solely determined by surface charge, when in high-salinity media. Here,
positively-charged particles underwent remarkable aggregation while negative ones were stabilized
and aggregates formation was limited upon interaction with EPS, prospecting an opposite
environmental destiny in marine ecosystems. Surface charge influenced ecotoxicity, with negative
PS NPs being generally non-toxic to microalgae and cyanobacteria. Positively-charge counterparts,
however, caused loss of cell viability and oxidative stress, but such effects were significantly reduced
when an eco-corona was present, suggesting a buffering action carried out by the adsorbed EPS layer,
capable of limiting direct NP-cell interactions and their resulting noxious effects. Overall, a
multifaceted scenario for bio-nano interactions in the marine environment emerges from this study,
with important ecotoxicological implications. If biological recognition of the biomolecular corona
seems the underlying mechanism to ecotoxic effects in complex biological milieus, mere physical
effects entailed by the eco-corona may be responsible for modulating the toxicity of NPs dispersed in
seawater. This fundamentally different characters of bio-nano interactions forecast an additional
dimension of complexity of nano-ecotoxicological research in the marine environment, worthy of
being considered in future studies
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
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