1,720,960 research outputs found
From Waste Vegetable Oil to a Green Compatibilizer for HDPE/PA6 Blends
Get PDFWhen properly compatibilized, the blending of polyethylene (PE) and polyamide (PA) leads to materials that combine low prices, suitable processability, impact resistance, and attractive mechanical properties. Moreover, the possibility of using these polymers without prior separation may be a suitable opportunity for their recycling. In this work, the use of an epoxidized waste vegetable oil (EWVO) was investigated as a green compatibilizer precursor (CP) for the reactive blending of a high-density PE (HDPE) with a polyamide-6 (PA6). EWVO was synthesized from waste vegetable cooking oil (WVO) using ion-exchange resin (Amberlite) as a heterogeneous catalyst. HDPE/PA6 blends were produced with different weight ratios (25/75, 75/25, 85/15) and amounts of EWVO (1, 2, 5 phr). Samples with WVO or a commercial fossil-based CP were also prepared for comparison. All the blends were characterized by scanning electron microscopy (SEM), differential scanning calorimetry (DSC), rheology, and mechanical tests. In the case of HDPE/PA6 75/25 and 85/15 blends, the addition of EWVO at 2 phr showed a satisfactory compatibilizing effect, thus yielding a material with improved mechanical properties with respect to the blend without compatibilizer. On the contrary, the HDPE/PA6 25/75 ratio yielded a material with a high degree of crosslinking that could not be further processed or characterized. In conclusion, the results showed that EWVO had a suitable compatibilizing effect in HDPE/PA6 blends with high HDPE content, while it resulted in unsuitable for blends with high content of PA6
3D printed piezoelectric scaffolds based on polyhydroxybutyrate and barium titanate for bone tissue engineering
No full textBone defects resulting from trauma, disease or surgery are a significant health problem worldwide. The significant healthcare costs required to manage this problem are further aggravated by the long healing times experienced with current treatment practices. Novel treatment approaches in the tissue engineering field, is using biomaterial scaffolds to stimulate and guide the regeneration of damaged tissue that cannot heal spontaneously. Therefore, bone tissue engineering aims to induce new functional bone regeneration through the synergistic combination of biomaterials and cells. Scaffolds provide a three-dimensional network that mimics the extra cellular micro-environment supporting the viability, attachment, and growth of cells. In particular, the porosity of biomaterials plays an essential role in the context of osteointegration and osteoconduction. The purpose of this work is to prepare and characterize new stimuli-responsive porous scaffolds to provide electric bio-signals naturally present in bone and vascular tissues. Processing techniques, such as mixing and extrusion, were used to create nanocomposites made by polyhydroxybutyrate (PHB) as matrix, a green polymer, biobased, biodegradable, and biocompatible, and the barium titanate (BaTiO3) nanoparticles as fillers, a piezoelectric and biocompatible nanoceramic with antibacterial properties. Nanocomposites, containing different percentages of BaTiO3 (5, 10, 15, 20 wt%), were created to prove the change of the polymer properties once the filler has been added. Processed materials were characterized in terms of morphological, thermal, and mechanical properties. Scanning electron microscopy results showed that the increase in the extrusion number can enhance the nanoparticles dispersion within the polymer matrix. In terms of mechanical properties considerable increases in the Young’s modulus and compressive strength were observed with the increase of the BaTiO3 content. Once nanocomposites were characterized, 3D printing was used to create 3D porous cubic scaffolds. The application of piezoelectric ceramics as a biomaterial processed via additive manufacturing represents a promising and novel approach in biomaterial manufacturing. The processing of the PHB/BaTiO3 nanocomposites was possible and resulted in the fabrication of interconnected, porous scaffolds with an average pore size of about 1 mm. The scaffolds were successfully fabricated using 90° lay down pattern with a continuous contour filament to achieve interconnected porous reticular structure. Temperature and injection speed were changed during the printing process to obtain good mechanical stability. Results from compression tests showed that the porous structure decreased their compressive strength compared to a filled cube of the same material, but, thanks to porosity, scaffolds seem to be good candidates for stem cells loading. Besides the promising results, the study also demonstrates that the fabricated scaffolds exhibit high microporosity through weak mechanical properties. Future investigations will focus on eliminating these disadvantages by a deeper investigation of the microstructure and alteration of the material composition. In conclusion, the additive manufacturing of piezoelectric PHB/BaTiO3-based nanocomposites represents a promising approach to yield scaffolds of designed porosity, equipped with piezoelectric properties for enhanced bone regeneration. The scaffold purpose is not to achieve the same mechanical properties of the natural bone, but to ensure the piezoelectric properties, due to nanoceramic presence, needed for cells stimulation until complete bone regeneration once the polymer matrix is degraded
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Get PDFWe 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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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