Number 746, September 21, 2005
by Phil Schewe and Ben Stein
Weighing the Amazon River
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 (U.S.), 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@osu.edu or Doug Alsdorf
at alsdorf@geology.ohio-state.edu
See also www.mps.ohio-state.edu
First Bose-Einstein Condensate 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 1023
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@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/cm2 and charging rates of 10
kHz.
Ma and Yang, Applied Physics Letters, 19 September 2005
Contact Yang Yang, UCLA, 310-825-4052, yangy@ucla.edu
Yang Yang laboratory's Web site
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