Superpropulsion of Droplets and Soft Elastic Solids

Drops of water found to spring from oscillating surface faster than the surface moves

(—A team of researchers with the University of Côte d’Azur in France has found that drops ejected by an oscillating surface can at times travel faster than the surface that ejected them. In their paper published in the journal Physical Review Letters, the team describes experiments they conducted by flinging water from a superhydrophobic surface and what they found.


We investigate the behavior of droplets and soft elastic objects propelled with a catapult. Experiments show that the ejection velocity depends on both the projectile deformation and the catapult acceleration dynamics. With a subtle matching given by a peculiar value of the projectile/catapult frequency ratio, a 250% kinetic energy gain is obtained as compared to the propulsion of a rigid projectile with the same engine. This superpropulsion has strong potentialities: actuation of droplets, sorting of objects according to their elastic properties, and energy saving for propulsion engines.

Cryogenic clocks will stay accurate for 16 BILLION years



Cryogenic optical lattice clocks

Ichiro Ushijima, Masao Takamoto, Manoj Das, Takuya Ohkubo & Hidetoshi Katori

Nature Photonics 9, 185–189 (2015) doi:10.1038/nphoton.2015.5
Received 13 May 2014 Accepted 06 January 2015 Published online 09 February 2015

The accuracy of atomic clocks relies on the superb reproducibility of atomic spectroscopy, which is accomplished by careful control and the elimination of environmental perturbations on atoms. To date, individual atomic clocks have achieved a 10−18 level of total uncertainties1, 2, but a two-clock comparison at the 10−18 level has yet to be demonstrated. Here, we demonstrate optical lattice clocks with 87Sr atoms interrogated in a cryogenic environment to address the blackbody radiation-induced frequency shift3, which remains the primary source of systematic uncertainty2, 4, 5, 6 and has initiated vigorous theoretical7, 8 and experimental9, 10 investigations. The systematic uncertainty for the cryogenic clock is evaluated to be 7.2 × 10−18, which is expedited by operating two such cryo-clocks synchronously11, 12. After 11 measurements performed over a month, statistical agreement between the two cryo-clocks reached 2.0 × 10−18. Such clocks’ reproducibility is a major step towards developing accurate clocks at the low 10−18 level, and is directly applicable as a means for relativistic geodesy13.


New ‘Cryogenic’ Clock Developed In Japan Accurate For 16 Billion Years

These new cryogenic clocks will stay accurate for 16 BILLION years