PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News Number 697
August 19, 2004  by Phillip F. Schewe, Ben Stein

NEWLY CREATED ANTIHYDROGEN ATOMS have been caught speeding for the first
time.  Owing to the vast preponderance of ordinary matter over antimatter
in the visible universe, and the propensity of any antimatter around to
annihilate hastily with any conventional particulate matter in the
vicinity, the only place anti-atoms exist on Earth for more than a
microsecond is in a chambered vault at the CERN Antiproton Decelerator (AD)
lab in Geneva.  There, antiprotons created artificially in high-energy
proton collisions and anti-electrons (positrons) from a radioactive source
are cooled and brought together in a bratwurst-sized vessel filled with
electrodes at various voltages.  By careful husbandry (first of all, the
antiprotons have to be slowed by a factor of 10 billion, from an energy of
5 MeV to .3 meV) anti-hydrogen (or H-bar) atoms are made from antiprotons
and positrons.  Although the anti-h's haven't yet been definitely fixed in
space or produced in their lowest quantum state (which is what you need to
do laser  spectroscopy), there are still other studies that can be made on
these very rare atoms as they mill about. (For some previous CERN anti-H
results see www.aip.org/pnu/2002/split/605-1.html and
www.aip.org/pnu/2002/split/611-1.html.)  One thing that can be done is to
measure the speeds of the anti-atoms by seeing how many of them emerge from
a region of oscillating electric fields without being ionized.  The ATRAP
collaboration, one of the CERN H-bar groups, has done exactly this.  They
have determined that the anti-atoms are moving with an average energy of
200 meV, which corresponds to a velocity only about 20 times that of the
thermal speed of an equivalent sample of atoms kept at a temperature of 4.2
K.  This is still too warm for the purpose of holding the anti-atoms in a
trap, but the researchers suspect that their current crop of anti-atoms
contains some with much lower velocities and that there will be a way to
cull an ever colder allotment in the future now that there is a speedometer
for antihydrogen atoms.  (Gabrielse et al., Physical Review Letters, 13
August; gabrielse{at}physics.harvard.edu, 33-450-28-38-95)
        
WHY ARE SEACOASTS FRACTAL? In a famous paper written decades ago, Benoit
Mandelbrot asked how long the coastline of Britain really was. The answer
depends on what kind of meter stick you use. The closer one looks at any
scale of a rocky coast map, from well above the 100 kilometer level to the
kilometer level, and so on to the meter level, the more indented and
lengthy the "coastline" becomes. Not only that, but the coast's
underlying geometry seems be fractal, meaning that it is extremely
fractured and also self-similar: the shape looks, in a statistical sense,
the same at all levels of magnification. Now, scientists in France have
inquired into the physical processes that actually could carve out a
fractal coast. Their simulation of a rocky coast evolution depends on an
iteration of erosion action. First, waves are allowed to erode the weak
points in a smooth shoreline. This makes the shore irregularly indented and
longer. This erosion exposes new weak points, but at the same time
mitigates the force of the sea by increasing the wave damping. These steps
are then repeated over and over. The resultant coast is fractal, with an
effective dimension of 4/3. According to Bernard Sapoval and A. Baldassarri
of the Ecole Polytechnique (Palaiseau, France) and their colleague A.
Gabrielli of the "Enrico Fermi" Center (Rome), this new study
provides the first suggestion of how a fractal shoreline comes about.
(Sapoval et al., Physical Review Letters, 27 August 2004
bernard.sapoval{at}polytechnique.fr, 33-169334172)

NANOTUBE DYNAMOS.  Two scientists in India have produced a tiny voltage in
a small electrical circuit by blowing gas across a mat of carbon nanotubes
and doped semiconductors. This result arises from two physical effects. 
First, in the Bernoulli effect, gas rushing past a surface produces
pressure differences along streamlines, which in turn can produce a
temperature gradient along a material sample.  Second, in the Seebeck
effect, a temperature gradient (the far ends of the material being at
different temperatures) can generate a voltage difference across the
sample.  In the experiment of Professor Ajay.K. Sood and his graduate
student Shankar Ghosh at the Indian Institute of Science (Bangalore) gas is
blown over a mat of carbon nanotubes as well as doped silicon and
germanium.  With a small sliver of germanium as a sample,  a voltage
difference of 650 micro-volts was generated.  The power flow amounted to 43
nano-watts.  This doesn't sound like much power, and the researchers have
not yet determined whether the effect could be scaled up (a no-moving-parts
carbon nanotube/doped-semiconductor generator of electricity), but one
definite near-term application would be in a new type of gas flow velocity
sensor for research in problems of turbulence or aerodynamics.   Compressed
air was used to produce the tiny amount of electricity, but even human
breath blown at the inclined sample produced a measurable result of several
micro-volts.  (Physical Review Letters, 20 August 2004;
asood{at}physics.iisc.ernet.in, shankar{at}physics.iisc.ernet.in)

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