Number 550, August 1, 2001
by Phil Schewe, James Riordon, and Ben Stein
Element 118 Has Been Erased from the Periodic
Table
In 1999 scientists
at LBL reported evidence for element 118 in high energy lead-krypton
interactions). Follow-up experiments at LBL and elsewhere (such as the
GSI lab in Germany) have failed to confirm the results. The LBL scientists
have now re-analyzed their data and conclude that the original evidence
was spurious. In a Physical Review Letters article,
they retract their claim for the discovery of element 118.
Insect Senses Suggest Novel Neural Networks
Animals gather information about their environments when sensory neurons
fire minute electrical signals in response to chemicals, light, sounds,
and other stimuli. Studying networks of neurons in animals and insects
can provide us with insight to the natural world as well as inspiration
for manmade networks to aid in computing and other applications.
A new model of neural networks, based on recent studies of fish and
insect olfactory systems, suggests a way that neurons can be linked
together to allow them to identify many more stimuli than possible with
conventional networks. Researchers from the Institute for Nonlinear
Science at the University of California, San Diego (M. Rabinovich, mrabinovich@ucsd.edu,
858-534-6753) propose that connections between neurons can cause one
neuron to delay the firing of another neuron. As a result, a given stimulus
leads to a specific time sequence of neural impulses. In essence, the
interconnected neurons include time as another dimension of sensory
systems through an encoding method called Winnerless Competition (WLC).
Using a locust antenna lobe exposed to fragrances such as cherry and
mint for comparison, the researchers found their model could identify
roughly (N-1)! (equal to (N-1) x (N-2) x ...x 2) items with a network
built of N neurons. That is, a ten neuron WLC network should be able
to identify hundreds of thousands as many items as a conventional ten-neuron
network, and the benefits increase as networks grow.
The WLC model helps explain how the senses of animals, insects, and
even humans can accurately and robustly distinguish between so many
stimuli. In other words, it is a mathematical rationale as to why a
rose, by any other name, would smell as sweet---but doesn't smell like
an onion. Ultimately, the WLC model may lead to high capacity, potent
computing networks that resemble an insect antenna or a human nose more
than a desktop PC. (M. Rabinovich et al, Physical Review Letters,
6 August 2001; text at Physics
News Select).
The Most Precisely Located Astronomical Object
The most precisely located astronomical object is PSR J0437-4715, a
nearby binary pulsar consisting of a neutron star and white dwarf in
orbit around each other. Because of the high precision spatial resolution
of the Parkes 64-m radio telescope in Australia and because the pulsar's
nearness permitted ample measurement of parallax, the three-dimensional
character and whereabouts of the pulsar system could be mapped with
great confidence.
For example, the proper motion, the angular rate of motion of the
object across our line of sight, was measured to be 140.892 (with an
uncertainty of .006) milliarcseconds per year. This value, and measurement
of several other parameters for this system such as the pulsar position
and parallax distance are, the researchers say, "known to accuracies
unsurpassed in astronomy." In addition the observations are in
accord with the theory of general relativity as to estimating the presumed
subtle loss of energy from the binary pair owing to the radiation of
gravitational waves. (van Straten et al., Nature, 12 July 2001;
wvanstra@mania.physics.swin.edu.au)
Delivery of Single Atoms on Demand
Delivery of single atoms on demand is now possible. Physicists at the
University of Bonn hold cold cesium atoms in a magneto-optic trap, but
can shuttle the neutral atoms, one a time, with great control over distances
up to a centimeter by shifting an additional laser-light interference
pattern serving as local potential well. This kind of conveyor belt
for atoms is expected to be of help in various quantum entanglement
experiments or as part of an atomic shift register. (Kuhr et al., Science,
13 July 2001; kuhr@iap.uni-bonn.de.)
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