SETI bioastro: FW: Physics News Update 785

From: LARRY KLAES (ljk4_at_msn.com)
Date: Tue Jul 18 2006 - 13:25:57 PDT

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    >From: physnews_at_aip.org
    >Reply-To: physnews_at_aip.org
    >To: ljk4_at_MSN.COM
    >Subject: Physics News Update 785
    >Date: Mon, 17 Jul 2006 13:22:31 -0400
    >
    >PHYSICS NEWS UPDATE
    >The American Institute of Physics Bulletin of Physics News
    >Number 785 July 17, 2006 by Phillip F. Schewe, Ben Stein,
    >and Davide Castelvecchi www.aip.org/pnu
    >
    >A NEW BEC MAGNETOMETER represents the first application for Bose
    >Einstein condensates (BECs) outside the realm of atomic physics.
    >Physicists at the University of Heidelberg have used a
    >one-dimensional BEC as a sensitive probe of the magnetic fields
    >emanating from a nearby sample. The field sensitivity achieved
    >thereby is at the level of magnetic fields of nanotesla strength
    >(equivalent to an energy scale
    >of about 10^-14 eV) with a spatial resolution of only 3 microns.
    >Some methods (such as scanning hall probe microscopes) can attain
    >finer spatial resolution and some methods (such as superconducting
    >quantum interference devices---SQUIDs) can attain higher magnetic
    >sensitivity, but for its range, the Heidelberg device has a region
    >of the sensitivity-vs-resolution space all to itself. Joerg
    >Schmiedmayer
    >and his colleagues are pioneers in advancing the young science of
    >integrated atom optics (see www.aip.org/pnu/2000/split/516-1.html ),
    >which seeks to guide atoms around microchips and exploit them for
    >future practical applications much as electronics manipulates
    >electrons in integrated circuits and photonics uses photons in
    >optoelectronic structures.
    >To see how the BEC measures the electromagnetic potential above a
    >surface consider that potential to be a landscape covered with peaks
    >and valleys. If now you flood the whole landscape with water you
    >would create an equi-potential flat surface at the top. To plumb the
    >submerged topography you could measure the total amount of the water
    >beneath the surface at any point. This is what the Heidelberg
    >researchers do. Across the sample, where the potential is deep
    >(that is, where the fields are particularly strong) more atoms in
    >the BEC pile up. Thus the density of atoms in the BEC (which can be
    >measured by seeing how much light from a probe laser is absorbed at
    >points along the length of the BEC---see figure at
    >http://www.aip.org/png/2006/261.htm ) can be converted into a map of
    >the fields at the sample surface. According to Schmiedmayer
    >(schmiedmayer_at_atomchip.org), the sensitivity of this process is
    >already so great that the measurement is limited to some extent by
    >"atomic shot noise," the atom equivalent of shot noise, the noise
    >encountered in measuring faint currents because of fluctuations in
    >the number of electrons arriving at a point a circuit or in
    >measuring light levels in a fiber because of fluctuations in the
    >number of arriving photons. In the BEC case, the field measurements
    >will be more robust against such atom shot noise if more atoms can
    >be loaded into the BEC, which resides in a tiny atom trap mere
    >microns from the surface under study, while simultaneously keeping
    >the chemical potential constant. The sensor's nT field sensitivity
    >and micron spatial resolution should make it useful for discovering
    >new solid state and surface physics phenomena. (Wildermuth et al.,
    >Applied Physics Letters, published online 27 June 2006; lab website
    >at www.atomchip.org )
    >
    >DUNE TUNES. For centuries, world travelers have known of sand dunes
    >that issue loud sounds, sometimes of great tonal quality. In the
    >12th century Marco Polo heard singing sand in China and Charles
    >Darwin described the clear sounds coming from a sand deposit up
    >against a mountain in Chile. Now, a team of scientists has
    >disproved the long held belief that the sound comes from vibrations
    >of the dune as a whole and proven, through field studies and through
    >controlled experiments in a lab, that the sounds come from the
    >synchronized motions of the grains in avalanches of a certain size.
    >Small avalanches don’t produce any detectable sound, while large
    >avalanches produce sound at lots of frequencies (leading to
    >cacophonous noise). But sand slides of just the right size and
    >velocity result in sounds of a pure frequency, with just enough
    >overtones to give the sound “color,” as if the dunes were musical
    >instruments. In this case, however, the tuning isn’t produced by
    >any outside influence but by critically self-organizing tendencies
    >of the dune itself. The researchers thus rule out various “musical”
    >explanations. For example, the dune sound does not come from the
    >stick-slip motion of blocks of sand across the body of the dune
    >(much as violin sounds are made by the somewhat-periodic stick-slip
    >motion of a bow across a string attached to the body of the
    >violin). Nor does the dune song arise from a resonance effect (much
    >as resonating air inside a flute produces a pure tone) since it is
    >observed that the dune sound level can be recorded at many locations
    >around the dune. Instead, the sand sound comes from the
    >synchronized, free sliding motion of dry larger-grained sand
    >producing lower frequency sound. The scientists---from the
    >University of Paris (France), Harvard (US), the CNRS lab in Paris,
    >and the Universite Ibn Zohr (Morocco)---have set up a website
    >(http://www.lps.ens.fr/~douady/SongofDunesIndex.html ) where one can
    >listen to sounds from different dunes in China, Oman, Morocco, and
    >Chile. (Douady et al., Physical Review Letters, upcoming article;
    >contact Stephane Douady at douady_at_lps.ens.fr)
    >
    >***********
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