1,721,027 research outputs found
Structure-Directing Agent for the Synthesis of TiO2-Based Drug Delivery Systems
No full textA series of titanium oxides was prepared by a surfactant template method (STM) and used as carrier to sustain the release of ibuprofen, chosen as model drug. The STM procedure provides an efficient method to prepare TiO2 matrices with both high surface area (if compared with those obtained with the traditional synthetic approach) and a well defined mesoporous texture. Some parameters of the synthetic procedure were varied: pH, surfactant and thermal treatment. The physico-chemical nature of the surface carriers were investigated by means of N2 physisorption measurements and FT-IR analyses. The effect of the drug amount on the release kinetic was also investigated. The drug delivery was evaluated in vitro in four different physiological solutions (simulating the gastro-intestinal tract) in order to analyze the behaviour of the TiO2-based systems if formulated as oral DDS. The optimized approach turns out to be a good alternative to the classical methods employed to prepare efficient TiO2-based drug delivery systems
Bioactive Glasses Containing Au Nanoparticles. Effect of Calcination Temperature on Structure, Morphology, and Surface PropertiesDOI:10.1021/la100472p
No full textBioactive glasses containing gold nanoparticles (AuNPs) have been synthesized via the sol-gel route usingHAuCl4 x 3H2O as gold precursor. The formation process of AuNPs was studied as a function of the thermal treatment,which induces nucleation of Au particles and influences their nature, optical properties, shape, size, and distribution.The physicochemical characterization indicates that the sample treated at 600 °C presents the best characteristics to beused as a bioactive material, namely high surface area, high amount of AuNPs located at the glass surface, presence ofmicropores, and abundant surface OH groups. In the case of samples either aged at 60 °C or calcined at 150 °C, AuNPsjust begin their formation, and at this stage the gel is not completely polymerized and dried yet. A thermal treatment athigher temperatures (900 °C) causes the aggregation of AuNPs, forming “AuMPs” (i.e., Au microparticles) in adensified glass-ceramic material with low surface area, absence of pores, and low number of surface OH groups. Thesefeatures induce in the glass-ceramic materials treated at high-temperatures a lower bioactivity (evidenced by SBFreaction), as compared with that exhibited by the glass samples treated at 600 °C
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
Synthesis and Characterisation of Strontium and Magnesium Co-Substituted Biphasic Calcium Phosphates
No full textMagnesium and strontium both play important roles in the growth of bone and so are
desirable ions for substitution into hydroxyapatite (HA) intended for use as bioinstructive bone
substitutes. A range of compositions were prepared by a solid state method based on the nominal
composition of HA (Ca10(PO4)6(OH)2), with various levels of strontium and/or magnesium
substitution: strontium-substituted HA (Ca8Sr2(PO4)6(OH)2), magnesium-substituted HA
(Ca9.8Mg0.2(PO4)6(OH)2 and Ca9Mg(PO4)6(OH)2), and strontium and magnesium co-substituted HA
(Ca7.8Sr2Mg0.2(PO4)6(OH)2 and Ca7Sr2Mg(PO4)6(OH)2). Materials were characterised by powder
X-ray diffraction, Fourier-transform infrared spectroscopy and Raman spectroscopy. These analyses
indicated that the co-substituted materials were composed of mixtures of strontium-substituted
hydroxyapatite and magnesium and strontium co-substituted β-tricalcium phosphate. In the
magnesium-substituted materials, increased magnesium content was related to increased proportion
of β-tricalcium phosphate phase, both with and without strontium co-substitution. The unsubstituted
and strontium mono-substituted materials, however, were pure apatite phase, suggesting that
magnesium was the destabilising factor in the phase compositions of the magnesium
mono-substituted and magnesium and strontium co-substituted material
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