Number 274, June 7, 1996 by Phillip F. Schewe and Ben Stein
A NEW MEASUREMENT OF COSMIC DEUTERIUM . By looking for signs of deuterium
in very distant gas clouds, backlit by an even more distant quasar (at
a redshift of 3.7), astronomers at UC San Diego have determined that the
ratio of primordial deuterium to hydrogen is 2.3 x 10**-5, a factor of
10 less than measurements reported by other groups in 1994. Primordial
in this case refers to the abundances relatively early after the big bang
as opposed to more recent eras by which time much deuterium will have been
consumed by fusion burning in stars. The new lower D/H estimates imply
that the overall early baryon (protons and neutrons) density was actually
higher than previously thought, although still far less than would be required
for the universe to eventually close back on itself. (David Tytler et al.,
Nature, 16 May 1996.)
THE PHYSICS OF CAR BATTERIES: Originally intending only to provide a
proper explanation of batteries for an undergraduate electromagnetism book
he is writing, Wayne Saslow of Texas A&M University (409-845-4841)
has uncovered new details of how car batteries work. A 12-volt car battery
connects six lead-acid cells end to end. Each cell consists of a lead (Pb)
electrode and a lead oxide (PbO2) electrode immersed in a solution of water
and sulfuric acid (H2SO4). The acid dissociates into H+ and HS04- ions.
When connected to an external circuit, the reactions at the electrodes
drive ion current within the cell and electron current in the external
circuit. Typical theories of electrochemical cells assume that the amounts
of positive and negative charge exactly balance (electroneutrality). However,
for a slow, steady discharge of the battery and idealized flat electrodes,
Saslow's analysis finds that there is an excess of HSO4- ions in the bulk
of the solution. Overall "global" electroneutrality is maintained
by an excess of H+ ions near the electrodes. In addition to painting a
more sophisticated picture for electrochemical cells, his results may have
implications for the study of ion channels in biological cells, and for
astrophysical plasmas, in which "local electroneutrality" is
conventionally assumed. Saslow's equations also offer insights on how to
design a cell which would provide maximum power at a uniform rate until
it becomes totally depleted. This would be relevant for the design of electric
vehicle power packs. (17 June, Physical Review Letters).
WORLD'S FASTEST COMPUTER . Scientists at the University of Tokyo have
achieved the highest peak speed for a computer performing a scientific
calculation: 1.08 Tflops (short for trillion floating point operations
per second). With their special-purpose GRAPE-4 machine, Junichiro Makino
(makino@chianti.c.u-tokyo.ac.jp) and Makoto Taiji perform simulations of
the complex interactions among astronomical objects such as stars and galaxies.
This type of simulation, referred to as an N-body problem because the behavior
of each of the N test objects is affected by all the other objects, is
particularly computation-intensive. Fortunately, two advances have made
possible ever-larger simulations. One is computer speed, which is up by
a factor of 100 over the past 10 years for the fastest computers. Another
is improved algorithms for conducting efficient calculations. GRAPE-4 reaches
its record speeds using 1692 processor chips, each performing at rates
of 640 Mflops. The Tokyo researchers hope to achieve petaflops (10**15
operations per second) by the turn of the century with a suite of 20,000
processors each operating at 50 Gflops. (Computers in Physics, July/Aug
1996.)
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