1,721,099 research outputs found
Iron from a geochemical viewpoint. Understanding toxicity/pathogenicity mechanisms in iron-bearing minerals with a special attention to mineral fibers
No full textIron and its role as soul of life on Earth is addressed in this review as iron is one of the most abundant elements of our universe, forms the core of our planet and that of telluric (i.e., Earth-like) planets, is a major element of the Earth's crust and is hosted in an endless number of mineral phases, both crystalline and amorphous. To study iron at an atomic level inside the bulk of mineral phases or at its surface, where it is more reactive, both spectroscopy and diffraction experimental methods can be used, taking advantage of nearly the whole spectrum of electromagnetic waves. These methods can be successfully combined to microscopy to simultaneously provide chemical (e.g. iron mapping) and morphological information on mineral particles, and shed light on the interaction of mineral surfaces with organic matter. This review describes the crystal chemistry of iron-bearing minerals of importance for the environment and human health, with special attention to iron in toxic minerals, and the experimental methods used for their study. Special attention is devoted to the Fenton-like chain reaction involving Fe2+in the formation of highly reactive hydroxyl radicals. The final part of this review deals with release and adsorption of iron in biological fluids, coordinative and oxidative state of iron and in vitro reactivity. To disclose the very mechanisms of carcinogenesis induced by iron-bearing toxic mineral particles, crystal chemistry and surface chemistry are fundamental for a multidisciplinary approach which should involve geo-bio-scientists, toxicologists and medical doctors
Gallic acid grafting modulates the oxidative potential of ferrimagnetic bioactive glass-ceramic SC-45
Full text linkSurface reactivity of amphibole asbestos. A comparison between two tremolite samples with different surface area
Full text linkSurface reactivity of a fibrous tremolite sample from Castelluccio Superiore (Italy) was investigated by means of free radical generation following incubation in H2O2solution buffered at pH 7.4, for several time points, ranging from 1 day to 1 month. Results obtained were compared with those of another fibrous tremolite sample (from Maryland, USA), with much smaller surface area. Structural, morphological, and chemical alterations induced on tremolite by incubation were investigated by HR-TEM/EDS. The generation of HO•and COO-•radicals following reaction of tremolite with H2O2or formate ion was investigated by spin trapping/EPR spectroscopy. The dissolution process and surface modification were slower for the Maryland sample, with lowest surface area. Surface modification indicated the occurrence of either low- or high-coordinated Fe centres on the surface, as well as the evolution of their nuclearity. In turn, iron centres determine the reactivity of the fibre surface and the yield of HO•and COO-•radical species. The evolution of radical reactivity over time was proved to be largely dependent on surface area, with the highest radical yield occurring for low-area tremolite incubated over long times. The experimental results obtained in this study as well as the comparison with previous studies further confirm that surface reactivity of mineral fibres and inorganic particles is not dependent on Fetotcontent per se, but is likely due to surface properties and occurrence of specific iron sites
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
Surface reactivity of amphibole asbestos. A comparison between crocidolite and tremolite
Full text linkAmong asbestos minerals, fibrous riebeckite (crocidolite) and tremolite share the amphibole structure but
largely differ in terms of their iron content and oxidation state. In asbestos toxicology, iron-generated free
radicals are largely held as one of the causes of asbestos malignant effect. With the aim of clarifying i) the
relationship between Fe occurrence and asbestos surface reactivity, and ii) how free-radical generation is
modulated by surface modifications of the minerals, UICC crocidolite and fibrous tremolite from Maryland
were leached from 1 day to 1 month in an oxidative medium buffered at pH 7.4 to induce redox alterations
and surface rearrangements that may occur in body fluids. Structural and chemical modifications and free
radical generation were monitored by HR-TEM/EDS and spin trapping/EPR spectroscopy, respectively.
Free radical yield resulted to be dependent on few specific Fe2+ and Fe3+ surface sites rather than total Fe
content. The evolution of reactivity with time highlighted that low-coordinated Fe ions primarily contribute
to the overall reactivity of the fibre. Current findings contribute to explain the causes of the severe asbestosinduced
oxidative stress at molecular level also for iron-poor amphiboles, and demonstrate that asbestos
have a sustained surface radical activity even when highly altered by oxidative leaching
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
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