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Heat quanta: Take that, Jim Green.



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Subj: Phys. Rev. Focus: 16 July 1998

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PHYSICAL REVIEW FOCUS
(http://publish.aps.org/FOCUS/)
from the American Physical Society
16 July 1998

Introductions to the Focus stories of the past week. (For the full
stories, go to the web address at the top of this message.)

THE QUANTUM OF HEAT FLOW
Physicists have known for over a decade that electrical
conductance can be quantized: Under the right conditions it cannot
have just any value, but comes only in units of the universal
conductance quantum. In the past year, researchers have discovered
that a similar quantization should occur for the conduction of
heat. For an extremely thin wire at temperatures close to absolute
zero, the heat conduction quantum should be "universal"--
independent of the shape and size of the wire and even the
material it is made of. In the 6 July PRL a pair of theorists puts
this concept on an even firmer footing by showing that it should
be observable in practical experiments.
(Phys. Rev. Lett. 81, 232; posted 9 July 1998.)

LANDING IN THE TRENCHES OF GALLIUM ARSENIDE
A helicopter pilot flying over midtown Manhattan would find it
easiest to land on top of a building, but a report in the 13 July
PRL suggests that in some cases molecules hitting a surface
perform the equivalent of flying between the skyscrapers to land
on the streets. According to the authors, bromine molecules (Br2)
hitting a particular gallium arsenide (GaAs) surface bind
exclusively with atoms in the second layer, which are only exposed
at narrow "trenches" and breaks in the top layer of the crystal.
They explain the surprising finding with a simple bonding theory.
The result could be important for semiconductor processing in the
future, as techniques are developed to more precisely control
surface properties.
(Phys. Rev. Lett. 81, 413; posted 13 July 1998.)

The correct citation for last week's story on needle ice crystals
is Phys. Rev. Lett. 81, 176.

COMING SOON to the P.R. Focus web site: direct links to AIP
stories about PRL papers and images on the home page.




"I scored the next great triumph for science myself,
to wit, how the milk gets into the cow. Both of us
had marveled over that mystery a long time. We had
followed the cows around for years - that is, in the
daytime - but had never caught them drinking fluid of
that color."
Mark Twain, Extract from Eve's
Autobiography