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 165  February 17, 1994

LEPTOQUARKS HAVE NOT BEEN FOUND at the Tevatron.
Certain theories seeking to unify the electromagnetic, weak, and
strong forces hold that in addition to the known families of
elementary particles---the quarks and the leptons---there should exist
another family, the leptoquarks, which would have both lepton and
quark-like attributes.  Scientists using the D0 detector at the Tevatron
proton-antiproton collider have sought in vain for evidence of
leptoquarks in interactions at the highest energy available at any
accelerator, 1.8 TeV. If they had existed within an accessible mass
range, leptoquarks would have been produced in pairs; each would
have decayed into an electron and a quark.  From the data, the
Tevatron scientists estimate a lower limit on the leptoquark mass of
133 GeV.  As if to illustrate the massiveness of the undertaking of
finding a new class of fundamental particles, the published paper
bears the names of 351 authors.  (S. Abachi et al., 14 February 1994,
Physical Review Letters.)

A SCANNING MAGNETIC FLUX MICROSCOPE, a device that
can map magnetic fields with a spatial resolution of about 80 microns
and a field sensitivity of 7 pico-Tesla-Hz**-1/2, has been developed
by a Maryland-Berkeley collaboration (contact Frederick Wellstood,
301-405-7649).  The detector uses a 77-K superconducting quantum
interference device to sense tiny magnetic fields from a sample which
moves back and forth beneath the SQUID in 1-micron steps.  For
practice, the scientists made a picture of the face of George
Washington as it appears on the one-dollar bill. The accurate likeness
is composed of the measurements of the enhanced fields in the
vicinity of the tiny droplets of magnetic ink used on all greenbacks. 
The scientific uses of the magnetic microscope include prospecting for
the characteristic fields emanating from microscopic nuggets of
superconductor buried inside otherwise non-superconducting samples. 
The microscope can also be used to image poorly-magnetic materials
such as thin copper patterns on printed circuit boards by measuring
the faint magnetic fields that arise from eddy currents induced in the
copper.  (R.C. Black et al., 3 January 1994, Applied Physics
Letters.)

MYSTERIOUS ATMOSPHERIC RADIO BURSTS have been
measured by the ALEXIS satellite, which patrols the sky for evidence
of nuclear detonations.  The radio bursts are much stronger than those
associated with lightning bolts and only seem to occur over Africa
and South America.  The best explanation given so far is that the
radio signals may be linked with equally mysterious light flashes seen
above certain thunderstorms.  (Science News, 12 Feb.)

THE GLOBAL POSITIONING SYSTEM (GPS) can determine
latitude and longitude for any spot on Earth with an uncertainty of
only 10 meters; the distance between two points hundreds of km apart
can be determined to within 1 cm.  GPS does this by relaying timing
signals from a network of satellites, each carrying an atomic clock,
to a receiver (sometimes a hand-held device) which calculates the
position from the relative time delay of the signals. In an essay in the
January 1994 Physics Today, MIT physicist Daniel Kleppner uses
GPS as a case study for demonstrating why science is a good
investment.  He recounts the slow, painstaking march of scientific and
technological advances---e.g., hydrogen-maser clocks,
microelectronics, high-speed data processing---that culminated in
GPS.