160,970 research outputs found
Impact of particle thermal treatment on dielectric properties of core-shell filled epoxy nano-composites
No full textThis paper presents the effect of Silica-Titania (SiO2@TiO2) core-shell nano-particles added into amine-cured epoxy composites, under three different particle treatment conditions: untreated, calcined at 250 ∘C and 450 ∘C , on the dielectric and structural properties of the bulk composite. Characterization was conducted using a range of methods Transmission Electron Microscopy (TEM), Fourier Transform Infra-Red Spectroscopy (FTIR), Raman Spectroscopy, Differential Scanning Calorimetry (DSC) and Broadband Dielectric Spectroscopy (BDS). TEM confirmed the synthesis of the core-shell architecture with denser shells at higher calcination temperatures. Raman spectroscopy showed an increase in the Ti-O-Ti network formation and orderliness with elevated temperature treatment. Incorporating untreated filler into epoxy reduces the bulk real permittivity, while the inclusion of calcined fillers leads to an increase. An additional ω relaxation was observed in imaginary permittivity spectra of nano-composites pointing towards altered molecular dynamics within the epoxy due to nano-particle addition. These findings highlight the role of core-shell nano-particles in modifying the dielectric properties of epoxy composites, whilst differentiating them from conventional nano-particles
On the post-curing thermal treatment of silicone rubbers: a study on electrical performance
No full textSilicone rubbers, particularly poly(dimethylsiloxane) (PDMS), are popular across various industrial applications, however notable issues arise from volatile cyclic siloxanes and their tendency to compromise their performance. This study investigates the electrical performance (DC conductivity, dielectric spectroscopy, DC breakdown) of two commercial PDMS products, before and after a post-curing treatment (200◦C, 4h). The tested materials, named PDMS A (RTV) and PDMS B (LSR), are chosen as they display distinct characteristics: they differ in terms of outgassing behavior and structural alterations during treatment. In particular, thermogravimetric analysis (TGA) reveal pronounced volatile removal in PDMS B, while Fourier transform infrared (FTIR) and Raman spectroscopy demonstrate pronounced structural alterations in PDMS A (crosslinking of unreacted long chains) promoted by post-curing. As expected, the electrical insulation performance is enhanced in both post-cured materials: the magnitude of this depends on the extent of two abovementioned aspects. The DC conductivity reduction follows the volatiles removal pattern (larger scale in PDMS B), while the ε’ and ε’’ values reduce following the structural alteration pattern (elimination of a relaxation peak in PDMS A). The DC breakdown strength enhancements are driven by structural variations rather than removal of volatiles
Numerical simulation of lightning strike damage to wind turbine blades and validation against conducted current test data
No full textThis paper presents a novel numerical approach to simulate lightning strike damage to equipotential bonding interfaces of wind turbine blades, and model validation based on high-current testing. Modern rotor blades are equipped with metal receptors to intercept the lightning leader and metal down conductors to conduct the lightning current, preventing the direct attachment to the CFRP spars. In such conditions, damage in the form of resin thermal degradation and sparks develop inside the blade at the equipotential bonding interfaces. Excellent correlation was found between the numerical predictions and test results in terms of current and temperature distributions. High temperatures were predicted at the sparking areas observed in the tests, which suggested that the damage is thermally activated. Thermogravimetric analysis data indicated that the epoxy pyrolysis process evolves in stages, and that sparking events are often initiated by release of gases and formation of small voids at temperatures lower than expected
Reducing the electrical anisotropy in unidirectional CFRP materials for wind turbine blade applications
No full textThe incorporation of composite CFRP in wind turbine blades while to allows for longer and lighter blades challenges the efficiencyectiveness of their lightning protection system. The electrical anisotropy of these CFRP materials is a key factor and affects their performance. The present study investigates the influence of adding Graphene Oxide (GO) nanoparticles in to CFRP as a means to improve their electrical conductivity in the transverse and through thicknessthrough-thickness directions. Epoxy resin containing GO in filler contents of 5wt% and 6wt% was prepared and infused in unidirectional (UD) laminates. The GO nanofiller was dispersed in the epoxy resin prior to the infusion by means of speed mixing. The sample morphology was examined by means of optical microscopy. DC electrical resistance measurements were conducted in the transverse and through thicknessthrough-thickness directions to quantify the influence of the nanofiller. In For both filler volume contents loadings an increase was observed for both the transverse and through thicknessthrough-thickness directions compared to the neat CFRP
Variations on the Author
No full text“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
Dielectric response in epoxy nanocomposites incorporating various nano-silica architectures
No full textThe molecular dynamics and physical mechanisms in dielectric nanocomposites are key to develop materials with tailored properties. The effect of the architecture of nanoparticles on the bulk properties is one such factor which needs to be studied and understood. The aim of this study is to investigate the effect of different core-shell structures on the bulk properties of the epoxy nanocomposites. TEM images confirm the successful synthesis of the core-shell and hollow nanoparticles. Epoxy nanocomposites filled with three types of nano-silica architectures, namely core (SiO2), core-shell (SiO2-SiO2) and hollow (h-SiO2) were prepared. They were characterised via broadband dielectric spectroscopy as a function of frequency in the range of 10-1-105 Hz and a temperature range of -160°C - 160°C. Besides well known relaxations, an additional so called SiOH relaxation is observed. Its intensity is proportional to the amorphous content of the nanoparticles. A distinct overlap between the epoxy β relaxation and SiOH relaxation is also observed, significantly affecting the intensity of the β relaxation. Finally, due to the presence of additional core-shell interface in case of SiO2-SiO2 filled nanocomposite two interfacial polarization peaks are observed. These preliminary findings illustrate noticeable effect of the architecture (additional interfacial polarization peak) and crystallinity (SiOH relaxation) of the nanoparticles on the dielectric behaviour of the nanocomposite.</p
Lightning Protection of Wind Turbine Blades – How Supersizing Has Created New Challenges for Nanodielectrics Research
No full textThis article reviews the implications of super-sizing in lightning protection of wind turbine blades and how polymer nanocomposites, with improved electrical and thermal performance, may be used to mitigate consequent issues
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
Larry O. Spencer, Conference Author Presentation
No full textGen. Larry O. Spencer, USAF (Ret.), author of Dark Horse: A Journey from the Horseshoe to the Pentago
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