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(a) An optically created temperature spot is moved to the right in a sheet of ice. The ice melts in front of the spot (right) and freezes behind it (left) and moves the fluid due to the difference in specific volume. (b) Pumping ice is possible along freely defined patterns such as the letters “nim.” The heating laser spot traces the letters nim at 10 Hz. The temporarily molten channels are wide and thick. We visualize the flow by overlaying differences of successive pictures of fluorescent polystyrene spheres, which are suspended in the ice. (c) The laser spot is focused from below and moved with galvanometric mirrors.
(a) Pump velocities depend on the ice temperature (open circles). The theory of Eq. (3) predicts the pump velocity. (b) When the fluid does not freeze along the channel, the residual negative pump velocities can be described by the theory of thermoviscous flow (Ref. 5). (c) The length of the thawed spot becomes more elongated for higher . (d) Stroboscopic image of the molten spot along a circular path, shown by the broken line.
Optically pumping across an ice-ice interface. [(a)–(c)] The fluorescent dye Cy5 was pumped across an ice-ice interface. The ice-ice interface was created by sandwiching distilled water to a thickness of . After cooling to a droplet of Cy5 in (150 mM NaCl in 15 mM sodium citrate) is pipetted at the chamber edge and pulled inside by capillary forces. The Cy5 solution freezes after making contact with the ice sheet and forms an interface with the frozen water. The inhomogeneous structure results from the freezing of the dye solution on a slow time scale.
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