PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 746   September 21, 2005  by Phillip F. Schewe, Ben Stein

WEIGHING THE AMAZON RIVER has been accomplished by watching the rise and
fall of the Earth's crust with a Global Positioning Service (GPS) unit over
several years as the river floods and drains during its seasonal cycles. 
GPS, through its network of satellites and carefully staged series of
signals timed with exquisite precision by atomic clocks, can provide
information about the position at the Earth's surface with horizontal
uncertainty of about 1 mm and a vertical uncertainty of about 9 mm. 
Repeated measurements made over several years yield velocity measurements
for any spot to an accuracy of about 1 mm/year.  Around the wide world, a
typical land movement up or down will be about 2 to 10 mm/year.  But in
large tropical drainage areas, with huge volumes of water pressing down on
a river channel and floodplain, the oscillation can be bigger.  Indeed, the
peak-to-peak amplitude reported in this present measurement amounts to
50-75 mm/year.  When the river is heavy, the land sinks down.  Later, when
the river lessens, the land rebounds.Scientists from the Instituto
Brasileiro de Geografia e Estatistica and the Instituto Nacional de
Pesquisas da Amazonas (Brazil), and from Ohio State University, the
University of Memphis, and University of Hawaii (US), saw the biggest
displacement in Manaus, Brazil.  One of the researchers, Michael Bevis of
Ohio State, said that they were surprised by the size of the oscillation. 
(Bevis et al., Geophysical Research Letters, 15 September 2005; contact
Mike Bevis at mbevis{at}osu.edu or Doug Alsdorf at
alsdorf{at}geology.ohio-state.edu; see also www.mps.ohio-state.edu ; article
at http://www.agu.org/pubs/crossref/2005.../2005GL023491.shtml )

FIRST BEC IN A SOLID.  A Bose-Einstein condensate (BEC) has been observed
in a solid material for the first time.  The BEC in this case is not a
collection of atoms but rather a collection of particle-like excitations in
the solid called "magnons." In the presence of extremely high
magnetic fields, atoms with an intrinsic magnetism of their own (as
represented by a spin vector) can be oriented all in one direction if the
field strength is larger than a certain value.  In this configuration a
small input of energy can tilt some of the spins out of the general
formation.  The successive tilting of spins can take the form of a wave
moving through the sample.  If also the temperature of the sample is
extremely low, then the moving wave can be considered as a particle-like
(or
quasiparticle) entity, much as mechanical vibrations in a solid can be
construed as sound waves or as phonons.  A magnon is such a moving
magnetic-spin disturbance.  What the present experiment observes is a
condensation of magnons if the magnetic field is lower than the critical
strength and the temperature is below a characteristic value.  The work was
carried out by a group of scientists from these institutions: Max Planck
Institute for Chemical Physics of Solids (MPI, CPfS), Dresden; JINR Lab,
Dubna; Oxford University; and Adam Mickiewicz University, Poznan.  They
used a antiferromagnetic material (in which the spins of neighboring atoms
tend to be alternately aligned up and down) with a chemical composition of
Cs2CuCl4.  The temperatures were in the mK range and the external magnetic
field used was at high as 12 T (120,000 gauss).  In an atomic BEC, dilute
vapors of atoms (typically a million or so at a time) are chilled until
they enter into a single quantum state, as if all the atoms were one atom.
In a magnon BEC what is formed is a monolithic static magnetic alignment in
the solid.  About 10^23 magnons participate in the condensation.  A magnon
BEC had been predicted several years ago but not realized unambiguously
until this work.  The evidence for condensation is that the material
undergoes a phase transition at a critical temperature dependent on the
size of the external field used.  What the researchers look for is a
significant change in the measured heat capacity (the energy needed to
raise the material's temperature by a certain amount).  (Radu et al.,
Physical Review Letters, 16 September 2005; contact Heribert Wilhelm,
wilhelm{at}cpfs.mpg.de )

SOLID-STATE SUPERCAPACITORS.  A new type of solid state device, prepared by
scientists at UCLA, may provide a better method for backing up memory
information on a computer in the case of a power failure.  A capacitor is
an electrical component for storing electrical energy in the form of
negative and positively charged opposing electrodes.  Its ability to do
this is measured in units of farads.  So called supercapacitors are perhaps
a thousand times better than ordinary capacitors by being much smaller in
size and by bringing the two electrodes closer together.  As a quick energy
storage platform, a supercapacitor can charge or discharge in a time of
mere microseconds to seconds, whereas batteries take minutes to hours. 
However, the energy density for batteries is much higher.  Hence many
believe that the ideal backup energy storage device would be a hybrid of
battery and supercapacitor.  To be useful in that role, however,
supercapacitors must be easily made and integrated onto chips.  Here's
where the UCLA model proves itself: its fabrication process is simple (a
simple dielectric layer of lithium fluoride sandwiched between Au, Cu, or
Al electrodes), it doesn't need an electrolyte (many other supercapacitors
are halfway toward being miniature batteries in that they need
electrolytes), and it can be integrated for device applications.  It
features a capacitance of tens of microfarad/cm^2 and charging rates of 10
kHz.  (Ma and Yang, Applied Physics Letters, 19 September 2005; contact
Yang Yang, UCLA, 310-825-4052, yangy{at}ucla.edu ; website, 
http://www.seas.ucla.edu/yylabs)

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