PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 638 May 22, 2003   by Phillip F. Schewe, Ben Stein, and James
Riordon

A SOLID STATE PLASMA, a lattice of beryllium ions (atoms from which
2 or 3 of the 4 electrons have been removed) remaining in solid
state form for a few nanoseconds, has been studied by physicists at
Livermore National Lab. This is done in two steps.  First, intense x
rays created by a powerful laser striking the outside of the coated
beryllium sweep into the beryllium and strip electrons as they go
by.  But in the short time before the solid dissipates, a second
laser striking a metal foil creates a beam of diagnostic x rays.
The scattered x rays reveal an electron density of more than 2 x
10^23 per cubic centimeter and an electron temperature of 600,000
K.  These conditions are hard to come by for plasmas in
low-atomic-number atoms like beryllium and the hydrogen isotopes
that will be the fuels in inertial confinement fusion.  Siegfried
Glenzer (glenzer1{at}llnl.gov) and his colleagues do their research as
part of the lead-up to fusion work at the National Ignition
Facility, where target pellets will undergo a compression up to 1000
times the normal solid state density.  (Glenzer et al., Physical
Review Letters, upcoming article; associated website,
http://www.llnl.gov/nif/ )

THE CONVENTIONAL THEORY OF DARK MATTER just got some potent support
from a new batch of observations to be reported by scientists from
the Sloan Digital Sky Survey (SDSS) this week at a meeting in the
Canary Islands.  One of the main reasons for believing in the
existence of non-luminous matter is that the motions of galaxies
within galaxy clusters and the motions of matter around individual
galaxies seems to defy conventional celestial mechanics. Either
plenty of extra (but unconventional) mass must lurk in the vicinity
of the galaxies (the dark matter theory) or the known laws of
physics might be in need of amendment (the theory known as modified
Newtonian dynamics, or MOND).  Scrutinizing a subset of 3000
galaxies (from Sloan's inventory of 250,000 galaxies) with satellite
galaxies in tow, the researchers' profile of satellite velocities
supported the dark matter theory and discounted the MOND idea.  (See
the Sloan website at www.sdss.org )

ORCA ACOUSTICS.  Echo-locating marine mammals help maneuver in the
deep by sending out sounds and listening for the response, a feat
requiring exquisite time resolution in distinguishing emitted clicks
from echos.  Recently a team of scientists from the Russian Academy
of Sciences and the University of Hawaii studied this process by
recording the auditory brainstem responses (ABRs) in a false killer
whale (Pseudorca crassidens).  The test animal was trained to
cooperate to the extent of accepting a suction-cup electrode (placed
behind the blowhole) for providing EEG signals and a willingness to
indicate whether it had detected the presence or absence of a
target.  The intensity of the emitted clicks is of course much
higher than the intensity of the returning echos but the amplitude
of the respective brainstem response (the animal listening to its
own clicks and to the echos) was roughly the same.  This suggested
to the researchers that some mechanism is at work helping to mask
out the emitted clicks while allowing the echos to be heard.  (Supin
et al., Journal of the Acoustical Society of America, May 2003;
contact Alexander Supin, a.supin{at}g23.relcom.ru)

A SPACE MISSION TO THE EARTH'S CORE is a project worth considering,
argues David Stevenson of Caltech.  Space, in this case, is not
empty vacuum but dense rock, and the "spacecraft" is not of the
Voyager class, but something like a grapefruit-sized seismic
detector.  It might work like this: With an explosive device of some
kind, a downward going crack in the Earth would be initiated.  Into
this crack would be pored a large supply of molten iron containing
the probe.  The metal-filled crack would "fall" downward owing to
gravity with a speed of about 5 m/sec and would close up behind as
it went.  As Stevenson points out, cracks in the Earth regularly
relay magma from the lower depths to the surface.  The probe, made
of a high-melting-point alloy, would essentially communicate with
the surface by sending out seismic waves.  Stevenson
(djs{at}gps.caltech.edu) advances the whole idea of directly probing
the Earth's core not as a well formulated plan but as a provocation
to scientific thinking.  The mission, he allows, might cost as much
as the unmanned space program but the scientific rewards could be
high: learning more about energy sources (such as radioactivity) at
great depths or the origin of hot spots (responsible, say, for
creating the Hawaiian islands), and other material properties of the
terrestrial core.  (Nature, 15 May 2003; website,
www.gps.caltech.edu/faculty/stevenson/coremission )

***********
PHYSICS NEWS UPDATE is a digest of physics news items arising
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