Characterization of Aerodynamic Forces on Wings in Plunge Maneuvers

We present experiments and simulations of plunging maneuvers of large amplitude, for velocity ratios of G=1 and 2, defined as the ratio between the peak plunge velocity and the freestream velocity. We explore the effect of the airfoil shape by considering a NACA 0012 wing and a flat plate. The experiments are performed with wings with aspect ratios of 4 and 4.86, whereas the simulations are performed using a model of an infinite-aspect-ratio wing. We report the time evolution of the force coefficients and flow visualizations. A good qualitative agreement is found between experiments and simulations, with small discrepancies in the maximum and minimum lift coefficients observed during the maneuvers and somewhat larger discrepancies during the postmaneuver phase. It is found that the airfoil shape has a small effect on the lift coefficient but a somewhat larger effect on the drag coefficient. We also perform a force decomposition analysis to relate vortical structures to the force on the wings, providing a quantitative measurement of the effect of the leading-edge vortex and trailing-edge vortex on the peak aerodynamic forces.This work was partially supported by the State Research Agency of Spain (AEI) under grant DPI2016-76151-C2-2-R, including funding from the European Regional Development Fund and the U.S. Air Force Office of Scientific Research under grant FA9550-16-1-0508. The computations were partially performed at the supercomputer Picasso from the Red Española de Supercomputación in activity FI-2019-1-0030.Publicad

Joule effect self-heating of epoxy composites reinforced with graphitic nanofillers

Self-heating of conductive nanofilled resins due to the Joule effect is interesting for numerous applications, including computing, self-reparation, self-post-curing treatment of resins, fabrication of adhesive joints, de-icing coatings and so on. In this work, we study the effect of the nature and amount of graphitic nanofiller on the self-heating of epoxy composites. The addition of graphitic nanofillers induced an increase in the thermal conductivity of the epoxy resins, directly proportional to the nanofiller content. Percolation was not observed because of the heat transport through phonons. In contrast, the electrical conductivity curves present a clear percolation threshold, due to the necessity of an electrical percolation network. The electrical threshold is much lower for composites reinforced with carbon nanotubes (CNTs, 0.1 wt.%) than for the resin filled with graphene nanoplatelets (GNPs, 5 %). This fact is due to their very different specific areas. The composites filled with CNTs reach higher temperatures than the ones reinforced with GNPs, applying low electrical voltage because of their higher electrical conductivity. In contrast, the self-heating is more homogeneous for the GNP/epoxy resins due to their higher thermal conductivity. It was also confirmed that the self-heating is repetitive in several cycles, reaching the same temperature when the same voltage is applied

Efecto combinado de grafeno y nanotubos de carbono en las propiedades de las resinas dopadas

En este trabajo se estudia la eficiencia de la adición de nanorrefuerzos grafíticos para la mejora de las propiedades de resinas epoxídicas. Para ello, se han obtenido dispersiones de nanotubos de carbono y nanoplaquetas de grafeno en resinas termoestables de calidad aeronáutica. Se ha confirmado que la adición de bajos contenidos de nanotubos aumenta la temperatura de transición vítrea de las resinas y su conductividad eléctrica, mientras que el grafeno aporta un interesante aumento de la conductividad térmica. Es por ello que se concluye que ambos refuerzos son complementarios e inducen mejoras del material en diferentes propiedades

Reducing the environmental impact of surgery on a global scale: systematic review and co-prioritization with healthcare workers in 132 countries

Abstract Background Healthcare cannot achieve net-zero carbon without addressing operating theatres. The aim of this study was to prioritize feasible interventions to reduce the environmental impact of operating theatres. Methods This study adopted a four-phase Delphi consensus co-prioritization methodology. In phase 1, a systematic review of published interventions and global consultation of perioperative healthcare professionals were used to longlist interventions. In phase 2, iterative thematic analysis consolidated comparable interventions into a shortlist. In phase 3, the shortlist was co-prioritized based on patient and clinician views on acceptability, feasibility, and safety. In phase 4, ranked lists of interventions were presented by their relevance to high-income countries and low–middle-income countries. Results In phase 1, 43 interventions were identified, which had low uptake in practice according to 3042 professionals globally. In phase 2, a shortlist of 15 intervention domains was generated. In phase 3, interventions were deemed acceptable for more than 90 per cent of patients except for reducing general anaesthesia (84 per cent) and re-sterilization of ‘single-use’ consumables (86 per cent). In phase 4, the top three shortlisted interventions for high-income countries were: introducing recycling; reducing use of anaesthetic gases; and appropriate clinical waste processing. In phase 4, the top three shortlisted interventions for low–middle-income countries were: introducing reusable surgical devices; reducing use of consumables; and reducing the use of general anaesthesia. Conclusion This is a step toward environmentally sustainable operating environments with actionable interventions applicable to both high– and low–middle–income countries

Chemical and electrical properties of LSM cathodes prepared by mechanosynthesis

Mechanosynthesis of La1-xSrxMnO3 (x = 0, 0.25, 0.5, 0.75 and 1) was carried out at room temperature from stoichiometric mixtures of La2O3, Mn2O3 and SrO, obtaining monophasic powders with the perovskite structure. Physical properties of these materials and their chemical compatibility with the electrolyte yttria stabilized zirconia (YSZ), which depend strongly on the La/Sr ratio, were evaluated to corroborate availability to be implemented as cathode material in solid oxide fuel cells (SOFCs). Electrical conductivity values in air ranged between 100 and 400 S cm-1 in the temperature range of 25-850 C. Samples presented low reactivity with YSZ in the working temperature range (600-1000 C) maintaining the grain size small enough to preserve the catalytic activity for oxygen reduction. © 2013 Elsevier B.V. All rights reserved.Peer Reviewe

Photocurable nanodoped resins

This work is focus on the development of photocurable resins doped with nanoparticles of very diverse nature, diamond, barium oxide, hydroxyapatite and silver. These nanoreinforcements are being investigated, and even applied industrially, as nanofillers of thermosetting resins, due to the different enhancements and new properties, including increased mechanical, thermal and chemical properties, high electrical and thermal conductivity, improved biocompatibility and antimicrobial properties, among others. The reinforcement of photocurable thermosetting resins can be complex since the added charge can exert shielding to the radiation, limiting to reach high curing degree. For it, it is necessary to use catalysts and sensitizers of UV radiation. In addition, in order to limit this negative effect, a high degree of dispersion of the nanofillers is required, avoiding the presence of micrometric agglomerates. An epoxy system has been selected, whose is commly used for dental applications, and differente contents of nanofillers have been added. Once the dispersion process has been optimized, the effect of the different fillers on the degree of curing of the photocurable resin, measured through its glass transition temperature, has been studied. The degree of curing achieved has been explained through transperance measurements to the visible light of the samples, as well as the morphology of the cured and doped resins

Hydrothermal ageing of graphene/carbon nanotubes/epoxy hybrid nanocomposites

The hydrothermal ageing of hybrid nanocomposites formed by carbon nanotubes (CNTs) and graphene nanoplatelets (GNPs) incorporated into an epoxy matrix was studied. In order to avoid the weak interface, amine functionalized GNPs were used which are reactive with the epoxy matrix. The content of CNTs was 0.1 wt% and the GNPs content ranged from 5 to 12 wt%. The isothermal water absorption was measured until very long times (almost two years). Reduction of water absorption with the addition of either carbon nanotubes or graphene nanoplatelets has been found independently of the ageing time. The results can be described by a two-stage diffusion model with the first and second stages being diffusion and matrix relaxation controlled respectively. The obtained diffusion coefficient for the neat epoxy thermoset is higher than those of nanocomposites, which decreases with the increase of GNPs content. Theeffect of water absorbed on the dynamic-mechanical properties and on the electrical conductivity of the nanocomposites was analyzed. Whatever the temperature the storage modulus shows a continuous increase with the increase of the nanoparticles content, the effect of hydrothermal ageing is to decrease the modulus only in the glassy state (T < Tg). Water aged specimens show broadening of the tanδ peak related to the plasticization of the matrix. Tg of aged specimens coincides with the one of the unaged matrix, indicating that hydrothermal ageing does not produce noticeable matrix damage even after two years. Water aged specimens show similar electrical conductivity than unaged ones,which is another indication of no degradation of samples by water

Optimization of a resin with carbon nanotubes ink for printing by Inkjet technologies

The main aim of this research is the development of a nanoreinforced thermosetting resin based ink to be used in injection printers for additive manufacturing processes.&nbsp; (inkjet tecnhnologies). Firstly, printing conditions have been optimized for the nanoreinforced epoxy resin at different MWCNT contents. Afterwards these inks have been used to print 2D circuits based on joined parallel straight lines. These printed materials were tested to evaluate their mechanical and electrical properties. MWCNT reinforced epoxy resin inks developed resulted in successful injection to produce the 2D circuits repetitively. The dispersion of the MWCNTs in the epoxy resin is adequate and the circuits containing 0.3 wt.% of nanoreinforcement were electrically conductive. Mechanical properties were similar for both materials