130,505 research outputs found
Mode-II fracture behaviour of aerospace-grade carbon fibre/epoxy composites interleaved with thermoplastic veils
No full textThermoplastic veils based on Polyethylene-terephthalate (PET), Polyphenylene-sulfide (PPS) and Polyamide-12 (PA) fibres (∼10μm in diameter) were used to interlay unidirectional (UD), non-crimp fabric (NCF) and 5-Harness satin weave (5H) carbon fibre laminates. The PET and PPS veils remained in a fibrous form and the PA veils melted during the laminate curing process. The results of an end-loaded split test demonstrated significant improvements in the mode-II fracture performance in all cases. In general, interlaying thermoplastic veils was most efficient for toughening the UD laminates, with reduced improvements observed for the 5H and NCF laminates, respectively. The main toughening mechanism of the intact PET and PPS veils was thermoplastic fibre bridging. The melted PA veils mainly improved the fracture toughness of the epoxy at the mid-plane. The different toughening mechanisms of the veils, combined with different fracture mechanisms between the UD, NCF and 5H laminates, resulted in significantly different toughening levels
Interlaminar fracture toughness of aerospace-grade carbon fibre reinforced plastics interleaved with thermoplastic veils
No full textThis work investigates the toughening performance of thermoplastic veils when used to interlay aerospace-grade CFRPs. Veils based on Polyethylene-terephthalate (PET), Polyphenylene-sulfide (PPS) and Polyamide-12 (PA) fibres (~10 μm in diameter) were used as interlayers of unidirectional (UD), non-crimp fabric (NCF) and 5-Harness satin weave (5H) carbon fibre/epoxy laminates. During a hot curing process of the laminates, the PET and PPS veils remained in a fibrous form, and the PA veils melted. This resulted in different toughening mechanisms, i.e. interlaying the PET and PPS veils introduced extensive thermoplastic fibre bridging, and adding the PA veils improved the fracture toughness of the epoxy matrix. The different toughening mechanisms of the veils, together with the different fracture mechanisms of the laminates, dramatically affected the toughening levels. In general, the PET and PPS veils were more effective for toughening the UD laminates, and the PA veils were superior for the NCF and 5H laminates
PCL-coated hydroxyapatite scaffold derived from cuttlefish bone: Morphology, mechanical properties and bioactivity
No full text[EN] In the present study, poly(epsilon-caprolactone)-coated hydroxyapatite scaffold derived from cuttlefish bone was prepared. Hydrothermal transformation of aragonitic cuttlefish bone into hydroxyapatite (HAp) was performed at 200 C retaining the cuttlebone architecture. The HAp scaffold was coated with a poly(c-caprolactone) (PCL) using vacuum impregnation technique. The compositional and morphological properties of HAp and PCL-coated HAp scaffolds were studied by means of X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA) and scanning electron microscopy (SEM) with energy dispersive X-ray (EDX) analysis. Bioactivity was tested by immersion in Hank's balanced salt solution (HBSS) and mechanical tests were performed at compression. The results showed that PCL-coated HAp (HAp/PCL) scaffold resulted in a material with improved mechanical properties that keep the original interconnected porous structure indispensable for tissue growth and vascularization. The compressive strength (0.88 MPa) and the elastic modulus (15.5 MPa) are within the lower range of properties reported for human trabecular bones. The in vitro mineralization of calcium phosphate (CP) that produces the bone-like apatite was observed on both the pure HAp scaffold and the HAp/PCL composite scaffold. The prepared bioactive scaffold with enhanced mechanical properties is a good candidate for bone tissue engineering applications.The financial support of the Ministry of Science, Education and Sports of the Republic of Croatia (project 125-1252970-3005: "Bioceramic, Polymer and Composite Nanostructured Materials") and from the Spanish Ministry project DPI2010-20399-C04-03 is gratefully acknowledged. Rocio Ochoa-Fernandez is also acknowledged for her help with the mechanical tests.Milovac, D.; Gallego-Ferrer, G.; Ivankovic, M.; Ivankovic, H. (2014). PCL-coated hydroxyapatite scaffold derived from cuttlefish bone: Morphology, mechanical properties and bioactivity. Materials Science and Engineering C. 34:437-445. https://doi.org/10.1016/j.msec.2013.09.036S4374453
Adhesion Improvement of Thermoplastics-Based Composites by Atmospheric Plasma and UV Treatments
No full textThe present work is concerned with adhesive bonding of thermoplastic composites used in general aerospace applications, including polyphenylene sulfide (PPS), polyetherimide (PEI) and polyetheretherketone (PEEK) carbon fibre composites. Three different surface treatments have been applied to the PEEK, PPS and PEI-based composites in order to enhance the adhesion: atmospheric plasma, ultraviolet radiation (UV) and isopropanol wiping as a control. Water contact angles and free surface energies were measured following the standard experimental procedure based on the employment of three different liquid droplets. Infrared spectroscopy and X-ray photoelectron spectroscopy (XPS) were subsequently performed to characterize the surface chemistry of the samples after treatment. The single lap joints were manufactured and bonded by an Aerospace grade epoxy-based film adhesive originally developed for use on metals but with the ability to bond treated thermoplastics to good strength (supplied by Henkel Ireland). Quasi-static (QS) tests were conducted. The lap shear strength was evaluated, and the failure mechanisms of the different joints were examined for the range of surface treatments considered. It was found that the performances of the PEEK and PPS joints were considerably improved by the plasma and UV treatments resulting in cohesive and delamination failures, while PEI was unaffected by the plasma and UV treatments and performed very well throughout
PCL-coated hydroxyapatite scaffold derived from cuttlefish bone: in vitro cell culture studies
No full text[EN] In the present study, we examined the potential of using highly porous poly(epsilon-caprolactone) (PCL)-coated hydroxyapatite (HAp) scaffold derived from cuttlefish bone for bone tissue engineering applications. The cell culture studies were performed in vitro with preosteoblastic MC3T3-E1 cells in static culture conditions. Comparisons were made with uncoated HAp scaffold. The attachment and spreading of preosteoblasts on scaffolds were observed by Live/Dead staining Kit. The cells grown on the HAp/PCL composite scaffold exhibited greater spreading than cells grown on the HAp scaffold. DNA quantification and scanning electron microscopy (SEM) confirmed a good proliferation of cells on the scaffolds. DNA content on the HAp/PCL scaffold was significantly higher compared to porous HAp scaffolds. The amount of collagen synthesis was determined using a hydroxyproline assay. The osteoblastic differentiation of the cells was evaluated by determining alkaline phosphatase (ALP) activity and collagen type I secretion. Furthermore, cell spreading and cell proliferation within scaffolds were observed using a fluorescence microscope. (C) 2014 Elsevier B.V. All rights reserved.The financial support of the Ministry of Science, Education and Sports of the Republic of Croatia (Project 125-1252970-3005: "Bioceramic, Polymer and Composite Nanostructured Materials"), the Spanish Ministry project DPI2010-20399-C04-03 and the L'Oreal ADRIA-UNESCO national fellowship program for Women in Science is gratefully acknowledged.Milovac, D.; Gamboa-Martinez, TC.; Ivankovic, M.; Gallego-Ferrer, G.; Ivankovic, H. (2014). PCL-coated hydroxyapatite scaffold derived from cuttlefish bone: in vitro cell culture studies. Materials Science and Engineering C. 42:264-272. https://doi.org/10.1016/j.msec.2014.05.034S2642724
Effect of in situ formed hydroxyapatite on microstructure of freeze-gelled chitosan-based biocomposite scaffolds
No full textNew in situ highly-porous chitosan/hydroxyapatite (CS/HA) biocomposite scaffolds have been prepared via freeze-gelation technique. Different content of in situ synthesized hydroxyapatite within chitosan solution was obtained by changing the amount of calcium and phosphate precursors. The composition of precipitated inorganic phase was characterized by X-ray diffraction analysis (XRD) and Fourier transformed infrared spectroscopy (FTIR), while morphology of scaffolds was imaged by scanning electron microscopy (SEM). SEM observations of cross section and surface area of prepared scaffolds have shown different microstructure and topography regarding to the HA content, which plays an important role in cell adhesion and proliferation, and nutrient transport. The MIT assay of scaffolds with different content of hydroxyapatite has shown no toxicity which is one of the main requirements for potential biomedical application. Likewise, the presented synthesis allows preparing the scaffolds with large and very well interconnected pores without obtaining toxic intermediate products.CIBER-BBN is an initiative funded by the VI National R&D&I Plan 2008-2011, Iniciativa Ingenio 2010, Consolider Program. CIBER Actions are financed by the Instituto de Salud Carlos III with assistance from the European Regional Development Fund.Rogina, A.; Rico Tortosa, PM.; Gallego-Ferrer, G.; Ivankovic, M.; Ivankovic, H. (2015). Effect of in situ formed hydroxyapatite on microstructure of freeze-gelled chitosan-based biocomposite scaffolds. European Polymer Journal. 68:278-287. https://doi.org/10.1016/j.eurpolymj.2015.05.004S2782876
MeSH term explosion and author rank improve expert recommendations
No full textInformation overload is an often-cited phenomenon that reduces the productivity, efficiency and efficacy of scientists. One challenge for scientists is to find appropriate collaborators in their research. The literature describes various solutions to the problem of expertise location, but most current approaches do not appear to be very suitable for expert recommendations in biomedical research. In this study, we present the development and initial evaluation of a vector space model-based algorithm to calculate researcher similarity using four inputs: 1) MeSH terms of publications; 2) MeSH terms and author rank; 3) exploded MeSH terms; and 4) exploded MeSH terms and author rank. We developed and evaluated the algorithm using a data set of 17,525 authors and their 22,542 papers. On average, our algorithms correctly predicted 2.5 of the top 5/10 coauthors of individual scientists. Exploded MeSH and author rank outperformed all other algorithms in accuracy, followed closely by MeSH and author rank. Our results show that the accuracy of MeSH term-based matching can be enhanced with other metadata such as author rank
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe 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
Rapid surface activation of carbon fibre reinforced PEEK and PPS composites by high-power UV-irradiation for the adhesive joining of dissimilar materials
No full textCarbon fibre reinforced poly-etherether-ketone (PEEK) and poly-phenylene-sulfide (PPS) composites were rapidly surface-treated by high-power UV light, and then adhesively bonded to aluminium 2024-T3 and carbon fibre/epoxy composites. The results of a single lap-shear joint test demonstrated that a UV-treatment lasting for 5 s was sufficient to prevent joint failure occurring at the composite/adhesive interfaces in all cases, e.g. it increased the failure strength of the PPS composite/aluminium joints from 11.1 MPa to 37.5 MPa. Moreover, the composite/adhesive interfaces performed well upon an exposure of the joints to an environment of high humidity and temperature for 8 weeks. Additionally, an investigation lasting for 6 months showed no degradation of the surface functionalisation from UV-irradiation. Overall, this work highlights high-power UV-irradiation a very promising method for surface preparation of thermoplastic composites (TPCs) for adhesive joining, i.e. TPC adhesive joints with excellent structural integrity can be obtained by using this rapid, eco-friendly and low-cost surface-treatment method
"Closing the R&D Gap, Evaluating the Sources of R&D Spending"
No full textBoth spending and tax policies have been implemented in the United States with the goal of stimulating private sector research and development (R&D). Karier questions whether current R&D policy, especially the research and experimentation tax credit, can contribute to closing the gap between nondefense expenditures on R&D in the United States and such expenditures in other countries, such as Japan and Germany. He also explores possible changes to our current R&D policy to make it more effective.
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