Number 860, April 10, 2008 by Phillip F. Schewe and Jason S. Bardi
Optical Clocks Get Better.
Two separate experiments in Colorado compare the frequency of emissions from atoms or ions to an uncertainty of 10^-16 or better. Earlier atomic clocks operated by reading out the movements of internal transitions from one quantum state to another in cesium atoms; the light emitted was in the microwave range. With frequency comb techniques (http://www.aip.org/pnu/2008/split/853-1.html) measurement of optical-range frequencies can also be made with high accuracy.
In the 28 March 2008 issue of Science two groups reported new superb levels of precision. One experiment, carried out by a JILA/Colorado/ NIST-Boulder team (Ludlow et al.), gauges the uncertainty of a clock based on neutral strontium atoms to a level of 10^-16 by comparing it to a clock using calcium atoms and located a kilometer away. The other experiment, carried out at NIST-Boulder (Rosenband et al), looks at two clocks 100 meters apart.
Observed by an Argonne-Novovsibirsk-Regensburg-Bochum collaboration in titanium-nitride films, is the antithesis of the superconducting state. In conventional superconductivity electrons pair up, and these pairs enter into a single quantum state in which current flows with zero electrical resistivity. By contrast, the titanium-nitride film studied here, while normally a superconductor at low temperatures, can be forced to become an insulator. Under a combination of conditions-the sample being a certain thickness and an external magnetic field being present-the lowering of temperature can actually reverse the electrical property of the material from one of zero resistivity to one of zero conductivity: in other words a perfect superinsulator. (Vinokur et al., Nature 3 April 2008).
Physicists at the University of Bordeaux have produced mini-storms resembling hurricanes in half-spherical soap bubbles. They’ve even produced the soapy equivalent of Jupiter’s Great Red Spot. The bubbles, 8 or 10 cm across, are heated at the equator and cooled at the pole. This heat differential sets up turbulence which sometimes can manifest itself as a Red Spot kind of swirl.
According to author Kellay Hamid (email@example.com) one feature that distinguishes the Bordeaux experiment in modeling fluid turbulence from previous efforts is the absence of a lateral wall in the fluid surface, in this case a hemispherical film. (Seychelles et al., Physical Review Letters, upcoming article)