Text 330, 74 rader
Skriven 2005-01-19 17:57:32 av Herman Trivilino (1:106/2000.7)
Ärende: PNU 716
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PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 716 January 19, 2005
by Phillip F. Schewe, Ben Stein

THE MOST DISTANT CRAFT LANDING IN THE SOLAR SYSTEM. The Huygens probe, given
long passage by the Cassini spacecraft into the middle of Saturn's minor
planetary system, has successfully parachuted onto the surface of Titan, the
only moon with a considerable atmosphere. Pictures taken from miles above the
surface during the descent and pictures taken on the surface itself suggest the
presence of boulders or ice chunks and some kind of shoreline, perhaps of a
hydrocarbon lake or sea.  The data gained so far include a sort of acoustic
sampling of the atmosphere during the descent and some color photographs.  The
Titan probe is named for Christaan Huygens, who first spotted Titan and who
also was the first to provide the proper interpretation of Saturn's ring
system.
(http://www.esa.int/SPECIALS/Cassini-Huygens/)

THE SOUND OF THE EARLY UNIVERSE. New published surveys of distant galaxies are
in accord with what you'd expect from standard big bang cosmology.  Precise
measurements of the cosmic microwave background provide in effect an image of
the cosmos just as the first atoms were forming about 400,000 years after the
big bang.  The lumpiness of this background testifies to the shepherding role
of gravity in establishing primitive structures.  Statistical studies of the
distribution of the tiny surpluses or deficits across the microwave sky suggest
that at this point in the early universe (corresponding to a redshift of 1000)
colossal sound waves were propagating through the primordial plasma.  Evidence
for these acoustic ripples moving through early matter has now been seen, again
in a statistical analysis, in the distribution of galaxies occurring billions
of years later.  Two large astronomical collaborations, the Two Degree Field
Galaxy Redshift Survey (2dF) and the Sloan Digital Sky Survey (SDSS), both
using automated telescopes dedicated to measuring lots of galaxy redshifts,
reported at last week's meeting of the American Astronomical Society in San
Diego that the present population of observed galaxies seems to have grown
steadily and consistently, through the agency of gravitational interactions,
out of the lumpy terrain of the earlier microwave background era.  The 2dF
catalog contains 221,000 galaxies, while SDSS's catalog has almost 47,000.
(Online papers, astro-ph/0501171, astro-ph/0501174; www.sdss.org,
www.aao.gov.au/2df/ )
                                        
ELECTRON CLOUDS CAN FREEZE INTO AN "ORBITAL GLASS" at low temperatures.  In the
modern picture of quantum mechanics, electrons take the form of "clouds" within
the atoms and molecules in which they inhabit.  The clouds, which have various
shapes such as spheres or dumbbells, represent the general boundaries within
which one may find an electron at any one measurement in time.  Typically,
processes involving electron clouds (more formally known as "orbitals") are
blazingly fast.  In the order of a femtosecond (10^-15 s), for example, an
electron orbital can make transitions between degenerate states (those
containing the same amount of energy), transforming from a vertical dumbbell to
a horizontal one with respect to some axis. Now, scientists have found evidence
that these and other orbital processes can slow down dramatically--to as long
as 0.1 seconds, a slowing by 14 orders of magnitude--for electrons in
low-temperature FeCr2S4, a spinel (class of mineral) with a relatively simple
crystalline structure. The researchers, who hail from the Center for Electronic
Correlations and Magnetism at the University of Augsburg in Germany (Peter
Lunkenheimer, Peter.Lunkenheimer@Physik.Uni-Augsburg.de) and the Academy of
Sciences of Moldova (a former Soviet republic), consider these frozen electron
orbitals in spinels to constitute a new class of material which they have
dubbed an orbital glass.  By measuring the response of the material to
alternating-current  electric fields in the audio- to radio-frequency range,
they found that processes involving non-spherical orbitals dramatically slow
down at low temperatures to form a glass-like state, in a manner very similar
to the arrest of molecular motion that occurs when glass blowers perform their
craft. It's not just the orbitals that slow down; the neighboring atomic nuclei
that surround the electrons also distort more slowly in response to the
glacially changing orbitals.  In contrast to conventional glasses, a complete
"freeze" of the electron clouds does not occur at the lowest temperatures.
Completely frozen orbitals are prevented by quantum-mechanical
tunneling: the clouds keep themselves moving by making transitions between
different low-energy cloud configurations even without the energy they normally
require. (Fichtl et al., Physical Review Letters, 21 January 2005)

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 * Origin: Big Bang (1:106/2000.7)