1,720,982 research outputs found
Biocompatible hybrid materials synthesized via sol-gel for aerospace applications
No full textThe health of astronauts, during space flight, is threatened by bone loss induced by microgravity, mainly attributed to an imbalance in the bone remodeling process. In the present work, the response to the microgravity of bone cells has been studied using the SAOS-2 cell line grown under the condition of weightlessness, simulated by means of a Random Positioning Machine (RPM). Cell viability after 72 h of rotation has been evaluated by means of WST-8 assay and compared to that of control cells. Although no significant difference between the two cell groups has been observed in terms of viability, F-actin staining showed that microgravity environment induces cell apoptosis and altered F-actin organization. To investigate the possibility of hindering the trend of the cells towards the death, after 72 h of rotation the cells have been seeded onto biocompatible ZrO2/PCL hybrid coatings, previously obtained using a sol-gel dip coating procedure. WST-8 assay, carried out after 24 h, showed that the materials are able to inhibit the pro-apoptotic effect of microgravity on cells
Bioactive Titania-Based Organic–Inorganic Hybrids Synthesized via Sol–Gel
No full textIn the present work, the synthesis of organic–inorganic hybrid (OIH)
materials for biomedical applications is described. Two types of OIH systems
are prepared by means of a sol–gel process, both consisting of a titania
matrix. The use of two different biocompatible thermoplastic polymers as
organic component is evaluated: the poly(-caprolactone) and the
poly(ether-imide). The formation of the hybrid structure is ascertained by
scanning electron microscopy, whereas the identification of the interactions
between the organic and the inorganic phases is obtained by using Fourier
transform infrared spectroscopy. Moreover, a preliminary evaluation of the
osseointegration ability of the obtained material is investigated by soaking the
synthesized OIHs in a simulated body fluid to follow the ability of the
materials to induce the hydroxyapatite nucleation. The results show that all
OIHs are bioactive and, thus, potentially suitable for the implants’ design
Inorganic polymers from alkali activation of metakaolin: Effect of setting and curing on structure
No full textGeopolymers, obtained by chemical reaction between aluminosilicate oxides and silicates under highly
alkaline conditions, are studied in this paper. The proposed mechanism of geopolymer setting and
hardening or curing consists of a dissolution, a transportation or an orientation, as well as a
polycondensation step. The aim of this paper is to investigate the influence of the curing time and
temperature, the relative humidity and the reagents temperature on the geopolymerization process in
order to obtain a resistant matrix usable for inertization of hazardous wastes. The evolution of the
process from the precursors dissolution to final geopolymer matrix hardening has been followed by
FTIR spectroscopy, X-ray diffractometry, SEM/EDS and leaching tests. The results show the significant
influence of both curing temperature in the curing stage and of the mould materials on the matrix
stability. The easy-to-run preparation procedure for a chemically stable metakaolin geopolymer
individuated can be summarized as reagents setting and curing at room temperature and material
mould which permits moisture level around 40%
Pure Al2O3 2SiO2 synthesized viaasol-gel technique as a raw material to replace metakaolin:Chemical and structural characterization and thermal behavior
Full text linkThe performance of alkali activated cements is strongly influenced by
mineralogical composition and the impurity content of metakaolin, their
aluminosilicate precursor. In this study, pure aluminosilicates were synthesized
via the sol-gel technique and the possibility of using them to replace metakaolin
was explored. The study of their thermal behavior by simultaneous
Thermogravimetry/Differential Thermal Analysis allowed the best temperature for
inducing their complete dihydroxylation to be determined. X-ray diffraction,
Fourier Transform Infrared Spectroscopy and Scanning Electron Microscopy
showed that, after calcination, the materials are amorphous, homogeneous, and
have a higher content of reactive Al(V) than metakaolin. The reactivity of the
materials was ascertained by a leaching test carried out in strong alkaline solution.
The quantification of the released aluminate and silicate species, carried out by
inductively coupled plasma atomic emission spectroscopy, provide results which
encourage the use of the synthesized materials in the preparation of alkali
activated cements and geopolymers
Thermal and biological properties of several composite materials prepared by sol-gel method.
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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
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