1,721,179 research outputs found
TGA coupled with FTIR gas analysis to quantify the vinyl alcohol unit content in ethylene-vinyl alcohol copolymer
No full textThermo-gravimetric analysis coupled to time/temperature-resolved FTIR spectroscopy of evolved gases was used to measure the vinyl alcohol units content in EVOH copolymer. Pure homopolymers were used as references. The quantitative analysis here proposed is based on the calculation of integral profiles relative to FTIR signals of water molecules evolved during the thermal degradation (pyrolysis) of vinyl alcohol units
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
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
Evolution and Reversibility of Host/Guest Interactions with Temperature Changes in a Methyl Red@Palygorskite Polyfunctional Hybrid Nanocomposite
Full text linkPalygorskite is a microporous clay mineral with several important applications, including use as dye nano-scaffold, due to its ability to incorporate apt guest molecules and form exceptionally stable composites. Such a property covers widespread fields of interest, from pottery pigments to light harvesting. In all these applications, the stability of these composites at progressively increasing temperatures is an important parameter to determine their condition of usage. This work investigates the nature and strength of the stabilizing host/guest interactions at the basis of the exceptional stability of the methyl red@palygorskite composite system, which undergo a dynamic but reversible evolution depending on the level of heating. A multi-technique analytical protocol involving synchrotron X-ray powder diffraction (S-XRPD) and thermogravimetric analysis (TGA) coupled with infrared spectroscopy (FT-IR) and gas chromatography (GC-MS) was followed, which allowed to sharply identify the species evolved during heating. Moderate temperatures (140°-300°C) cause stabilization of H-bonds between the structural H2O and the carboxyl group of the dye, whereas higher ones (> 300°C) trigger formation of direct COOH/octahedral Mg bonds favoured by dehydration. Cooling below 300°C implies gradual reversibility of the observed trend due to rehydration from environmental moisture; additional heating (> 400°C), conversely, causes methyl red decomposition, fragmentation and further expulsion from the host tunnels ( 500°C). The encapsulated dye in zwitterionic, trans and/or protonated form affects the hosting system properties, preventing structural folding and strongly modifying the mechanism of water release for both structural and zeolitic H2O. Experimental results were interpreted also with the help of structural models obtained by molecular mechanics simulations, offering atomistic insights on the mechanisms at the basis of the observed phenomena
Evolution of host/guest interactions with heating in a palygorskite/methyl red (Maya Red) hybrid composite
No full textAn exceptionally stable hybrid material, fit for possible use as an innovative, cheap and ecologic pigment in the Cultural Heritage and Materials Science fields, can be obtained by grinding and heating palygorskite clay with the methyl red dye (2 wt%).
Due to its multiple analogies with the famed Maya Blue pigment (an ancestor of modern hybrid materials formed by indigo incorporation in palygorskite/sepiolite clay minerals), such a red/purple adduct can be considered an analogous Maya Red composite.
As per its renowned blue predecessor, the chemical and photo-thermal stability observed for this red equivalent is achieved through methyl red diffusion and bonding within the palygorskite tunnels, which occurs after heating or evacuation of a properly ground clay/dye mixture. Specific interactions form inside the host pores between the clay framework and dye reactive groups, contributing to ensure the composite stabilization at different temperatures.
An innovative, in-line coupled TGA-FTIR-GC-MS, synchrotron XRPD and molecular mechanics approach was performed on both pristine palygorskite and the related composite with methyl red with the aim to monitor the development of the interactions formed between the host and the guest while progressively heating. Such a study evidenced that several kinds of bonds can exist and differently affect this complex stability, each characterized by a specific binding energy and subjected to a dynamic but reversible evolution as a function of the magnitude of the heating treatment.
Weak to moderate temperatures (120-300°C) trigger zeolitic H2O loss and methyl red diffusion but do not imply release of Mg-coordinated OH2, which acts as H-bond donor to the dye carboxyl group. More severe heating (300-490°C) causes a two-step structural OH2 loss and triggers a ligand-displacement mechanism which favors straight interactions between octahedral Mg and the dye COOH acceptor atoms (i.e. oxygen).
Reversibility and shift between these different host/guest interactions severely affect the dehydration/rehydration process of the host framework, compared to the pristine clay. Several interrelated phenomena mutually interact in a sort of positive feedback: guest incorporation inside the tunnels prevents structural folding typical of pure palygorskite and modifies the release of both zeolitic H2O and structural OH2, consequently influencing both the nature and the strength of the host/guest interactions. Such a situation is further complicated by the different polymorphs of palygorskite (monoclinic and orthorhombic) showing peculiar and distinct behaviors, which concern both their affinity to form specific bonds with the encapsulated dye and the release of structural OH2 while heating.
Sheltering granted by incorporation in the host pores dramatically enhances methyl red thermal stability, whose degradation is likely to occur at temperatures sensibly higher than those decaying the isolated dye
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
Gallic acid grafting modulates the oxidative potential of ferrimagnetic bioactive glass-ceramic SC-45
Full text linkAppropriate 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
Surface 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
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