Browsing by Keyword "Microgravity"
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Item Low-gravity combustion synthesis: Theoretical analysis of experimental evidences(2006-11) Locci, A. M.; Licheri, R.; Orrù, R.; Cincotti, A.; Cao, G.; De Wilde, J.; Lemoisson, F.; Froyen, L.; Beloki, I. A.; Sytschev, A. E.; Rogachev, A. S.; Jarvis, D. J.; EXTREMATThe results obtained during a parabolic flight campaign sponsored by ESA on March 2002, and related to the combustion synthesis of TiB2 - xTiAl and TiB2 - xTiAl3 composites are reported. Besides classical SHS experiments performed using cylindrical pellets, combustion front quenching experiments using conical samples placed inside a copper block are also conducted. Similar experiments are carried out under terrestrial conditions, for the sake of comparison. As expected, under both low-gravity and terrestrial conditions, it is found that combustion temperature and front propagation velocity decrease as the system exothermicity is reduced, that is, when the aluminide/diboride molar ratio is augmented. However, it is observed that reaction front propagates relatively slower under low-gravity conditions. Consistently, the extinction of the combustion front occurs earlier when the reaction is performed under reduced gravity conditions. A theoretical analysis performed by means of appropriate dimensionless numbers is proposed to provide possible explanations of the main experimental evidences reported in the literature on this subject, including those shown in this work. Specifically, this analysis reveals that the relatively higher-propagation velocity observed under terrestrial conditions may be due to the correspondingly lower-sample porosity change, which in turn limits the thermal conductivity decreasing in the reaction zone. In addition, free convection phenomena taking place in the molten phase formed at the reaction zone are able to justify the difference in combustion wave velocity experimentally observed under terrestrial conditions between top and bottom ignition configurations. Moreover, it is found that finer microstructure typically observed under low-gravity is likely a consequence of the reduced coalescence phenomena taking place in such conditions.Item Perception of affordances during long-term exposure to weightlessness in the International Space station(2015-09-01) Bourrelly, Aurore; McIntyre, Joseph; Luyat, Marion; Robótica MédicaOn Earth, visual eye height (VEH)—the distance from the observer’s line of gaze to the ground in the visual scene—constitutes an effective cue in perceiving affordance such as the passability through apertures, based on the assumption that one’s feet are on the ground. In the present study, we questioned whether an observer continues to use VEH to estimate the width of apertures during long-term exposure to weightlessness, where contact with the floor is not required. Ten astronauts were tested in preflight, inflight in the International Space Station, and postflight sessions. They were asked to adjust the opening of a virtual doorway displayed on a laptop device until it was perceived to be just wide enough to pass through (i.e., the critical aperture). We manipulated VEH by raising and lowering the level of the floor in the visual scene. We observed an effect of VEH manipulation on the critical aperture. When VEH decreased, the critical aperture decreased too, suggesting that widths relative to the body were perceived to be larger when VEH was smaller. There was no overall significant session effect, but the analysis of between-subjects variability revealed two participant profile groups. The effect of weightlessness was different for these two groups even though the VEH strategy remained operational during spaceflight. This study shows that the VEH strategy appears to be very robust and can be used, if necessary, in inappropriate circumstances such as free-floating, perhaps promoted by the nature of the visual scene.Item Sintesi autopropagante ad alta temperatura in condizioni di microgravità(2003-07) Licheri, Roberta; Orrú, Roberto; Cao, Giacomo; De Wilde, Jimmy; Beloki, Inigo Agote; Jarvis, David John; Froyen, Ludo; EXTREMATSelf-propagating high temperature synthesis (SHS) under microgravity conditions was studied. The green density of the reacting sample also influenced SHS processes since it affected system reactivity and thermal conductivity of the compact. Either for the case of cylindrical pellets or during combustion front quenching (CFQ) experiments, temperature during reaction evolution was measured using thermocouples embedded in the pellet.