SETI bioastro: PHYSICS NEWS UPDATE 542

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From: Larry Klaes (larry.klaes@incent.com)
Date: Mon Jun 11 2001 - 07:03:16 PDT


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Subject: update.542

PHYSICS NEWS UPDATE
                      
The American Institute of Physics Bulletin of Physics News

Number 542 June 7, 2001 by Phillip F. Schewe, Ben Stein, and
James Riordon

THE SLOAN DIGITAL SKY SURVEY (SDSS) has just released
a monster data set, containing redshift information for 50,000
galaxies and 500 quasars, including for the first time the detection
of quasars with redshifts above a value of 6. The SDSS so far can
be considered as a sort of transcription process for mapping a
three-dimensional scattering of galaxies spread across a 500-
square-degree panel of sky onto a 500-gigabyte store of computer
data and made universally available for the common good. Over its
5 year tenure the survey hopes to log as many as 100,000 quasars.
The SDSS data release and quasar results were announced at this
week's meeting of the American Astronomical Society in
Pasadena. The Sloan 2.5-meter telescope in New Mexico looks
not just out to the edge of the universe but also views foreground
objects as well. For instance, in Pasadena SDSS scientists also
reported an inventory of asteroid belt objects orbiting between
Mars and Jupiter. Careful color analysis suggests that silicate
asteroids preferentially shelter towards the inner side of the belt, at
an average orbital radius of 2.8 astronomical units (AU), whereas
carbonaceous asteroids circle the sun a bit further out, at an
average radius of 3.2 AU. (Sloan press release, June 5;
http://www.sdss.org/sdss.html; for a lengthy discussion of the
Sloan project see Science, 25 May 2001.) Meanwhile another
mapping survey, the Two-degree Field (2dF) Galaxy Redshift
Survey, using a telescope near Coonabarabran, Australia,
announced plans to release on June 30 a sample of 100,000 galaxy
redshifts and spectra. (2dF press release, June1;
www.mso.anu.edu.au/2dFGRS/.)

CURRENT DENSITIES IN MGB2 SUPERCONDUCTORS look
promising. In pondering the discovery of a new family of
superconductors, such as the MgB2 materials reported first at a
meeting in January, one often asks first about the critical
temperature at which the material becomes superconducting. But
no less important are the critical current and the critical field,
which are respectively the maximum amount of current that can be
carried and the maximum magnetic field that can be sustained
without the material losing its superconductivity. In this regard
notable progress is reported in the 31 May issue of Nature. A
Wisconsin-Princeton group (Eom et al.) announced having
measured current densities of 1 mega-amp/cm^2 at a magnetic
field of 1 tesla and 10^5 amp/cm^2 in a field of 10 tesla for a thin
film of MgB2. Meanwhile a group at Lucent Technologies (Jin et
al.) current density of 85,000 amp/cm^2 in iron-clad wires of
MgB2.

THE CRACK OF A BASEBALL BAT, one of the most pleasing
sounds of any sport, also provides much-needed physical
information to an outfielder trying to judge where to run to catch a
fly ball. At this week's meeting of the Acoustical Society of
America in Chicago, Yale physicist Robert Adair (203-432-3370,
adair@hepmail.physics.yale.edu) explains that the collision of bat
and ball produces its characteristic crack (having a frequency of
about 500 Hertz) by expelling about 100 cm^3 of air in less than
1/2000 of a second. However, hitting the ball poorly (far away
from the bat's "sweet spot") causes the bat also to undergo energy-
sapping vibrations, which produces a lower-frequency sound wave
(having a fundamental frequency of 170 Hz) and combining with
the crack to produce a dull, broadband "clunk." Whether the ball
is hit with a crack or clunk provides crucial information to an
outfielder 300 feet away from home plate. If he depended solely
on looking at the trajectory of the ball, it would take, Adair
estimates, around 2 seconds to determine from his line of sight
whether the ball lands 50 feet in front of him or behind him. But
the sound arrives at him 0.3 seconds after the ball hits the bat,
providing an important early clue of where to go. Metal bats in
college baseball, however, provide fewer acoustical clues,
according to Dartmouth's Robert Collier, who is also speaking at
the ASA meeting. Well-hit and poorly hit balls sound similar with
those bats, but there are other clues, Adair points out, such as
looking at the batter's swing. (Lay language writeup by Adair at
http://www.acoustics.org/press/141st/adair.html)


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