Mechanical model of the ultrafast, carnivorous plant Utricularia
The underwater traps of the carnivorous plants of the
Utricularia species catch their preys through the repetition of an
"active slow deflation / passive fast suction" sequence. In this
paper, we propose a mechanical model that describes both phases and
strongly supports the hypothesis that the trap door acts as a flexible
valve that buckles under the combined effects of pressure forces and
the mechanical stimulation of trigger hairs, and not as a panel
articulated on hinges. This model combines two different approaches,
namely (i) the description of thin membranes as triangle meshes with
strain and curvature energy, and (ii) the molecular dynamics approach,
which consists in computing the time evolution of the position of each
vertex of the mesh according to Langevin equations. The only free
parameter in the expression of the elastic energy is the Young's
modulus E of the membranes. The values for this parameter are
unequivocally obtained by requiring that the trap model fires, like
real traps, when the pressure difference between the outside and the
inside of the trap reaches about 15 kPa. Among other results, our
simulations show that, for a pressure difference slightly larger than
the critical one, the door buckles, slides on the threshold and
finally swings wide open, in excellent agreement with the sequence
observed in high-speed videos.
***
LV11835AR
Interfacing ultracold atoms with quantum electronics
We show that electrons flowing quantum-mechanically through a semiconductor nanostructure can trap and control atoms less than a micron above the chip surface. The temperature of the atoms is eleven orders of magnitude smaller than that of the nanostructure – low enough to form a Bose-Einstein condensate.
This new hybrid quantum system, in which ultracold atoms above the nanostructure couple to electrons within it, has the potential to make microchips whose functionality far exceeds that of existing electron-only devices by offering extreme sensitivity and control. Even the smallest possible quantised chip current can imprint rewritable patterns in the condensate. Conversely, the condensate itself can be used for non-invasive functional imaging of quantum electronic devices.
In previous structures, atoms have been trapped by passing current through thick metal wires on the chip surface. But high current noise, combined with a strong quantum pull that the chip exerts on the atoms, destroyed traps closer than a few microns from the surface.
Our work shows that thin quantum conductors fabricated in a two-dimensional electron gas – already used in mobile telephones – overcome these limitations by reducing the current noise by three orders of magnitude, thus opening the way to creating miniature hybrid atom chips.
