[tt] Physics News Update 860

Fri Apr 11 10:11:57 UTC 2008

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From: physnews at aip.org
Date: Wed, 9 Apr 2008 15:34:58 -0400
To: eugen at LEITL.ORG
Subject: Physics News Update 860
Reply-to: physnews at aip.org

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 860   April 9, 2008      www.aip.org/pnu
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.  The clocks
contain respectively a single aluminum and a single mercury ion.
The fractional uncertainty in the ratio of the frequency outputs for
the clocks was determined to be 5.2 x 10^-17.  (NIST information at
http://www.nist.gov/public_affairs/clock/clock.html )

A SUPERINSULATING STATE, 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).

SOAP-BUBBLE JUPITER.  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
(h.kellay at cpmoh.u-bordeaux1.fr) 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)

***********
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