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 171  April 1, 1994


FASTER TECHNIQUES FOR SEQUENCING DNA, described
at the American Physical Society (APS) March
Meeting in Pittsburgh, may contribute to the
Human Genome Project.  With the conventional
technique, known as gel electrophoresis, in
which DNA fragments are separated by electric
fields, it would take 20,000 man-years to
determine the complete sequence of 3 billion
"base pairs" that make up the human genetic
code.  In a modification of electrophoresis that
uses thinner gels and higher electric fields,
Lloyd Smith of the University of Wisconsin can
now sequence a 500 base-pair DNA fragment in an
hour, as opposed to the 12-14 hours it takes
normally.  Brian Chait of Rockefeller University
has devised a sequencing method that completely
bypasses the use of a gel.  In his method, a
laser pulse would zap DNA fragments, converting
them into gaseous ions which would then fly
towards a detector to be analyzed.  Once his
technique is refined, Chait estimates that an
amount of DNA code that normally takes several
hours to sequence could be analyzed in less than
a minute.  Other researchers in Pittsburgh
proposed sequencing methods based on
photolithography techniques and single-molecule
detection.

PUNCTUATED EQUILIBRIUM is the name for Harvard
paleontologist Stephen Jay Gould's theory that
evolution comes about not just by gradual steps
but sometimes because of catastrophic events,
such as meteor impacts.  Kim Sneppen of the
Niels Bohr Institute in Denmark, speaking at the
APS meeting, believes that evolutionary bursts
may also occur because of the dynamics of
ecological systems themselves.  Sneppen and his
colleague Per Bak of Brookhaven have proposed a
model in which biological species can exhibit
"self-organized criticality," according to which
some systems, such as sand dunes or geological
faults, can accommodate the gradual addition of
energy or stress or small increments of matter
until a certain threshold is crossed, after
which a catastrophic reordering takes place,
such as an earthquake or avalanche.  Sneppin's
model, employing various rates of mutation and
interactions among species, seems to forecast
such avalanches for biological systems.
(Science News, 26 March 1994.)

WOMEN IN PHYSICS account for only 15% of
bachelor's degree recipients, 11% of new PhD's,
and only 3% of tenured or tenure-track positions
in the U.S.  This compares poorly with the
comparable numbers for many other nations with
advanced physics establishments.  For example,
recent women physics PhD percentages were 18% in
Germany, 21% in France, 12% in Britain, and 25%
in the former Soviet Union.  In the other
direction, the number for Japan was only 4%.
(Science, 11 March 1994.)

NEUTRINO OSCILLATIONS, the transformation of one
neutrino type (electron, muon, or tau) to
another, is invoked to explain the solar
neutrino problem: a detector designed to monitor
electron-type neutrinos from the sun will fail
in its job if, on the way to Earth, electron
neutrinos are turning into muon neutrinos.  A
new generation of terrestrial experiments
searching for neutrino oscillation are now being
planned.  All involve accelerator-produced
neutrinos and the study of their fluxes at
various points along a baseline.  One scheme
uses neutrinos from CERN in Switzerland and a
detector at Gran Sasso in Italy, 732 km away.
Another experiment involves shooting neutrinos
from Fermilab, near Chicago, up to the Soudan II
detector in Minnesota. (Science, 18 Feb.)