1,721,020 research outputs found
Structural characterization of erbium containing glasses by using molecular dynamics simulations
No full textErbium containing glasses cover an important role in optical communications such as optical amplifiers. It is well know that the concentration of erbium into the glass influences the optical response of the material, therefore in the last years particular attention was devoted to the analysis and characterization of the erbium local distribution in the glass network. The presence of high erbium concentration in the glass is correlated to the formation of Er3+ based clusters and this inhomogeneous distribution of the rare earth ions induces changes in the energy transfer between neighbouring ions leading to the concentration quenching of luminescence, experimentally observed for this class of optical materials. In this communication, the structural evolution occurring in the erbium sites, its modifier role and the changes induced by the alumina addition in the glasses have been extensively studied by using molecular dynamics technique. The effect of alumina on the clustering effect, typical of the glasses containing high erbium concentration, was defined for three main systems characterized by the presence of increased percentage of erbium oxide in the glass formulation
Montmorillonite as drug delivery system for gentamicin
No full textClays are common ingredients in pharmaceutical and cosmetic formulations as active substances (gastrointestinal protectors, osmotic oral laxatives, antidiarrhoeaics, topical antibacterials and antinflammatories) and excipients in solid forms (tablet, capsules, powder), liquid forms (suspensions, emulsions) or semisolid forms (ointments, creams). Only some clay minerals, a combination of Al or Mg octahedra and Si tetrahedra (phyllosilicates), including kaolin, talc, smectites and fibrous clays have beneficial effects in dermatological and cosmetic applications (geotherapy, palotherapy) according to their rheological and thermal properties as well as cation exchange capacity (CEC) and absorption. More, the intercalation of several drugs or cosmetic substances in smectites could represent an advantageous approach to design delivery systems for the topical use. Clay-drug interaction affects the properties of both the dosage form (viscosity, flow property) and the intercalated drug (stability , release, absorption).Among the mineral clays, montmorillonite (MMT) has high specific surface area and it exhibits good adsorption ability, cation exchange capacity, standout adhesive ability and drug-carrying capability. As a result of clay structural and chemical characteristics, montmorillonite, a 2:1 (ratio of silica tetrahedra to aluminium and/or magnesium octahedra) layered silicate, can accomodate therapeutic compounds between the layers generating a host for oral and topical drug delivery.The present work aims to evaluate the intercalation of gentamicin molecules into MMT clay to obtain a modulating drug delivery carrier for antibiotic skin treatment. More, clay antibacterial activity could produce a synergistic effect.The intercalation process of gentamicin into the MMT interlayer at different pH value and drug concentration was examined. MMT-gentamicin hybrid was characterized by X-ray diffraction, Fourier transformed infrared, ultraviolet-visible spectroscopy, thermal analysis, differential scanning calorimetry and molecular dynamics simulation
Montmorillonite as efficient carrier of gentamicin used for antibiotic treatment: comparison of MD simulations with experiments
No full textThe presented work shows the potential of a montmorillonite-based clay mineral (bentonite) to contribute to the development of novel antibiotic materials. In our knowledge, it is the first time the have been tested the intercalation of gentamicin molecules in montmorillonite as a drug delivery carriers for antibiotic treatment.Comparison of experimental measurements (XRD, TGA, DTA) with simulations (MD modelling) have provided a more detailed understanding of the geometry, organization of gentamicin molecules confined in the cationic clay. By MD simulations it has been possible obtain a further insight into the interactions between the organic guest and the clay framework in view to optimize the cationic exchange process
Microstructural Characterisation and Electrical Properties of Multiwalled Carbon Nanotube/Glass-Ceramic Nanocomposites
No full textWe report on an improved processing method for fabricating multiwalled carbon nanotubes/glass-ceramic nanocomposites based on vanadium doped silicate glass matrices. Starting from the design of a stable aqueous dispersion of CNTs, achieved using a cationic surfactant, the interaction of CNTs with glass particles in suspension was improved using a co-solvent that provided access to nanocomposites exhibiting high quality CNT distribution in the matrix, which was confirmed by detailed micro/nano-structural and morphological characterisation. Considering that very few studies have focused on the functional properties of CNT/glass composites, in the present investigation the electrical resistivity of CNT/glass composites was measured and it was demonstrated that higher electrical conductivity values were obtained compared to previous similar materials fabricated by conventional powder processing
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
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