PHYSICS NEWS UPDATE A digest of physics news items prepared by Phillip F. Schewe, AIP Publ

 
PHYSICS NEWS UPDATE
A digest of physics news items prepared by Phillip F. Schewe, AIP
Public Information
Number 162  January 31, 1994

THE FIRST DIRECT OBSERVATION OF STRUCTURE IN THE COSMIC MICROWAVE BACKGROUND
(CMB) has been made by a team of astronomers using a telescope at Tenerife,
in the Canary Islands.  Two years ago the Cosmic Background Explorer (COBE)
detected structure in the CMB at a level of 1 part in 100,000 over angular
swatches of 10 degrees.  This structure, however, was inferred from
statistical correlations in the underlying data and did not correspond to
the blue and red clumps one saw in the famous COBE maps of the entire sky.
The Tenerife measurements, in contrast, directly display primordial
fluctuations in the temperature of the CMB (variations about an average
value of 2.7 K) at a level of 2 parts in 100,000 over 5-degree chunks of the
sky, for the portion of the sky covered by the Tenerife survey.  These
features would not correspond to any supercluster we would see today since
the largest such structure would still subtend an angular size of less than
1 degree when projected onto the CMB.  The Tenerife and COBE results are
consistent with each other.  For example, the quadrupole component of the
CMB fluctuations is calculated to be 26 +/- 6 microkelvins for Tenerife and
17 +/-5 for COBE.  (S. Hancock et al., Nature, 27 January 1994.)

ATOM-BOMB SIZED METEOROID EXPLOSIONS in the Earth's atmosphere occur many
times a year.  In general, meteors will fragment upon entering the upper
atmosphere because of friction.  Smaller fragments will burn up but the
larger ones may actually explode, at altitudes of 20 miles or so.  Data from
military satellites being made public for the first time reveal the scope of
these meteoroid blasts: an average of 8 events a year were observed to have
an energy equivalent to a small nuclear bomb, although the true occurrence
may be 10 times larger.  Scientists estimate that every 10 million years we
should receive a catastrophic hit that would devastate life forms over much
of the planet, much like the dinosaur-killing impact 65 million years ago.
Much of the military data were originally gathered in an attempt to
discriminate between meteoroid blasts and manmade nuclear explosions.  (The
New York Times, 25 Jan; Sky & Telescope, Feb 1994.)

INTERMETALLIC SUPERCONDUCTORS operate in a much colder temperature regime
than ceramic superconductors, but may still be important for industrial
purposes.  A Y-Pa-B-C material developed at AT&T Bell Labs (Robert Cava,
908-582-2180) is superconducting at 23 K, the highest transition temperature
yet for a bulk intermetallic compound (Nature, 13 Jan. 1994).  This
material, at least for now however, is multi-phase, meaning that several
phases---each with its own structure---are present in the sample.  This
complicates the study of superconductivity properties.  The same team of
scientists has now reported a single-phase material, Ln-Ni-B-C, which
suerconducts at 16.6 K (Nature, 20 Jan).  The AT&T scientists believe that
these represent the first of what may be a new family of intermetallic
superconductors with useful properties.  For example, they might facilitate
higher magnetic fields than are possible with existing low-temperature
superconductors used in making wire, such as Nb-Sn.