From: LARRY KLAES (ljk4_at_msn.com)
Date: Wed Sep 21 2005 - 20:11:18 UTC
>From: physnews_at_aip.org
>Reply-To: physnews_at_aip.org
>To: ljk4_at_MSN.COM
>Subject: Physics News Update 746
>Date: Wed, 21 Sep 2005 15:59:45 -0400
>
>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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