Browsing by Issue Date, starting with "2022-03-22"
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- The Addition of Particles to an Alternative Jet FuelPublication . Ferrão, Inês; Mendes, Miguel; Moita, A. S.; Silva, AndréThe expansion of the research on nanoscale particles demonstrates several advantages in terms of stability and an increased surface area to volume ratio compared to micron-sized particles. Based on this, the present work explores the addition of aluminum particles in hydrotreated vegetable oil (HVO), an alternative jet fuel. To evaluate the influence of particle sizes, nano and micron particles (40 nm and 5 μm) in a particle concentration of 0.5 wt.% were stably suspended in HVO. This study evaluates droplet combustion with an initial diameter of 250 μm in a drop tube furnace under different furnace temperatures (600, 800, 1000 °C). A high magnification lens coupled with a high-speed camera provides qualitative and quantitative data regarding droplet size evolution and micro-explosions. Pure HVO and Jet A-1 were also tested for comparison purposes. The results reveal that the addition of aluminum particles enhances the alternative jet fuel combustion. Furthermore, decreasing the particle size and increasing the furnace temperature enhances the burning rate compared to the pure HVO. Pure HVO presents a burning rate nearly to 1.75 mm2/s until t/D20 = 0.35 s/mm2 at T = 1000 °C. When nanoparticles are added to HVO in a particle concentration of 0.5 wt.%, an improvement of 24% in burning rate is noticed. Conventional jet fuel and pure HVO do not present any disruptive burning phenomena. However, when aluminum particles were added to HVO, micro-explosions were detected at the end of droplet lifetime, regardless of the particle size.
- How spatial constraints afford successful and unsuccessful penetrative passes in elite association footballPublication . Travassos, Bruno; Monteiro, Ricardo; Coutinho, Diogo; Yousefian, Farzad; Gonçalves, BrunoThe aim of the present study was to examine the spatial relations between teams (macrolevel) and groups of players (meso-level) that afford successful penetrative passes (off-ball advantage) in elite football. Three balanced home matches from a Premier League team with 91 ball possessions in which a pass was performed into the opposition defensive area and overpassed the first defensive line, promoting a perturbation of the defensive team equilibrium, were selected for analysis. The spatial relations between teams were measured through spatial variables that captured the areas occupied by the teams, while the spatial relations between players were measured through variables that captured the distances and angles between attacking and defending players near the ball. Results revealed, at the macro-level, higher values of width ratio between teams and the width of the attacking team for unsuccessful penetrative passes (UPP), when compared to successful penetrative passes (SPP). At the meso-level, a general decrease in distances and an increase in angles between attacking and defending players were observed between successful to unsuccessful penetrative passes. These findings highlight the importance of using positional data analysis to identify teams’ tactical profiles and to potentiate coaches’ interventions.