(Continued from previous message)

electronic properties.
Therefore, the theorists suggest making differential measurements of the
Casimir force.  Together with experimentalists at IUPUI and Lucent, they
would compare the Casimir force for plates made with different metal
isotopes of the same element. Isotopes of an element have fairly identical
electronic properties, but different nuclear and gravitational properties.
If there is a difference between the measured Casimir forces, the
researchers can attribute it to new physics after other effects (such as
sample preparation) are taken into account. (Isotopes do affect the plates'
electronic properties slightly, but the researchers compute the resulting
change in Casimir force to be tiny compared to other effects, about 10,000
times smaller than the magnitude of the Casimir force itself.) Their
technique has another advantage: by directly measuring Casimir force
differences, rather than the force itself, they reduce the dependence upon
theoretical assumptions.  (Krause and Fischbach, Physical Review Letters, 4
November 2002; also Fischbach, Krause, Decca, Lopez, Physics Letters A,
upcoming).

TOOTH AND NAIL.  The architecture of many living creatures combines soft
organic tissue with hard inorganic crystal.  How do the hard parts develop
while up against the soft parts?  To examine this issue, physicists at
Northwestern University have grown an inorganic lattice (barium fluoride,
BaF2) directly beneath a two-dimensional crystalline array of organic
molecules (a fatty acid). Using the diffraction of synchrotron radiation
from these planar arrays, the researchers observe the structure of the two
lattices and also affirm that the two become commensurate (that is, they
register with each other), the first time this has been done in an
experiment.  Even though the lattice spacings of the BaF2 and the organic
monolayer are different, each contributes toward a compromise, the barium
fluoride structure by contracting just a bit, and the molecules by expanding
their spacing at one end: picture the molecules as a stack of pencils
standing on end and then being tilted a bit, modifying the spacing of the
pencil tips (figure at www.aip.org/mgr/png/2002/167.htm).  BaF2 is not a
biologically important mineral, but the Northwestern scientists (contact
Pulak Dutta, 847-491-5465, pdutta{at}northwestern.edu) expect to look directly
at biomineralization in an upcoming phase of their work.   Furthermore,
since growing two or more incommensurate materials next to each other (an
important operation in the microelectronics industry) is difficult because
of the unequal atomic spacings, the new research might in the long run be
able to lessen or end the currently stringent need for high vacuum to make
epitaxially grown materials. (Kmetko et al., Physical Review Letters, 28
Oct)

***********
PHYSICS NEWS UPDATE is a digest of physics news items arising
from physics meetings, physics journals, newspapers and
magazines, and other news sources.  It is provided free of charge
as a way of broadly disseminating information about physics and
physicists. For that reason, you are free to post it, if you like,
where others can read it, providing only that you credit AIP.
Physics News Update appears approximately once a week.

AUTO-SUBSCRIPTION OR DELETION: By using the expression
"subscribe physnews" in your e-mail message, you
will have automatically added the address from which your
message was sent to the distribution list for Physics News Update.
If you use the "signoff physnews" expression in your e-mail message,
the address in your message header will be deleted from the
distribution list.  Please send your message to: listserv{at}listserv.aip.org
(Leave the "Subject:" line blank.)


---
 þ OLXWin 1.00b þ Each day a day goes by.