Wavepackets falling under a mirror
  We depict and analyze a new effect for wavepackets falling freely under a barrier or well. The effect appears for wavepackets whose initial spread is smaller than the combination $\ds \sqrt{\frac{l_g^3}{|z_0|}}$, between the gravitational length scale $\ds l_g = \frac{1}{(2 m^2 g)^{1/3}}$ and the initial location of the packet $z_0$. It consists of a diffractive structure that is generated by the falling and spreading wavepacket and the waves reflected from the obstacle. The effect is enhanced when the Gross-Pitaevskii interaction for positive scattering length is included. The theoretical analysis reproduces the essential features of the effect. Experiments emanating from the findings are proposed. 
G. K\"albermann (Soil and Water department, Faculty of Agriculture,   Hebrew University, Israel)