RESUMO
The shear flow of ordinary liquids is for the first time observed at the submillimeter scale by thermal imaging. We report on microinfrared experiments, showing that liquids as important as water flowing on wetting surfaces produce cooling, while the academic view would foresee heating production. This apparent counterintuitive cooling effect shows that the increase of the internal energy due to the flow can result in different shapes, including a cooling process, before reaching the conventional heating regime at higher shear rates. This unknown property might be interpreted as a transient stretching state of the liquid. Shearing liquids might be a promising alternative compared to conventional endothermic processes (gas expansion or vaporization of a liquid, the Peltier effect, and so forth).
RESUMO
Observations with the Hubble Space Telescope (HST), conducted since 1990, now offer an unprecedented glimpse into fast astrophysical shocks in the young remnant of supernova 1987A. Comparing observations taken in 2010 with the use of the refurbished instruments on HST with data taken in 2004, just before the Space Telescope Imaging Spectrograph failed, we find that the Lyα and Hα lines from shock emission continue to brighten, whereas their maximum velocities continue to decrease. We observe broad, blueshifted Lyα, which we attribute to resonant scattering of photons emitted from hot spots on the equatorial ring. We also detect N v λλ1239, 1243 angstrom line emission, but only to the red of Lyα. The profiles of the N v lines differ markedly from that of Hα, suggesting that the N4+ ions are scattered and accelerated by turbulent electromagnetic fields that isotropize the ions in the collisionless shock.