RESUMO
We directly observe the hydrodynamic linear response of a unitary Fermi gas confined in a box potential and subject to a spatially periodic optical potential that is translated into the cloud at speeds ranging from subsonic to supersonic. We show that the time-dependent change of the density profile is sensitive to the thermal conductivity, which controls the relaxation rate of the temperature gradients and hence the responses arising from adiabatic and isothermal compression.
RESUMO
Fast colloidal motions driven by surface tension gradient are created in a thin water layer. Unlike using solid boundaries to limit the colloidal flow, our work relaxes this condition by directly placing bulk fluid next to an open air environment. When the colloidal flow along the air/water interface is interfered with stationary objects, repetitive semicircular motions, that is, micro eddy, are frequently observed in domains as small as 2 µm. We assign the capillary convection between the liquid next to the air and that from the bulk as the driving force for the observed motions. Relationships among the maximum speed, temperature gradient, and thickness of the liquid layer are experimentally investigated and numerically analyzed. Our results could inspire future designs of micromechanical motors or fluidic mixing in a miniature device.