Number 278, July 8, 1996 by Phillip F. Schewe and Ben Stein|
EXTREMELY HIGH ENERGY COSMIC RAYS show a slight preference as to their
directionality. With no accelerators to boost particles above the trillion-electron-volt
(TeV) range, scientists look to cosmic rays for supplying not only the
highest particle energies but also hints about what must be a tremendous
energy machine at work in our galaxy or beyond. This is especially true
of cosmic rays with EeV (10**18 eV) energies. A new study of 36 cosmic-ray
events recorded with the Akeno Giant Air Shower Array (AGASA) in Japan
shows that mostly they are distributed uniformly across the sky. A notable
departure from this general pattern consists of three pairs of events whose
directions of arrival are quite close, less than 2.5 degrees. And of these,
two pairs are located within 2 degrees of the supergalactic plane, defined
roughly by the agglomeration of bright nearby galaxies in the northern
hemisphere. The Akeno scientists (Motohiko Nagano, email@example.com)
suggest that most likely some kind of celestial accelerator lies in the
direction of the collimated pairs. (N. Hayashida et al., Physical Review
Letters, 5 August 1996.)
MINIMAL ENERGY REQUIREMENTS IN COMMUNICATIONS. In 1948, information-theory
pioneer Claude Shannon showed that sending messages through conventional
systems (such as the movement of electrons down a copper wire) without
errors requires adding enough energy to the signal to make it roughly as
strong as the amount of noise present. This may be true for most communications
channels but not for all, IBM physicist Rolf Landauer (914-945-2811) says.
He points out that some communication mechanisms could be more robust in
weathering a noisy environment. For example, a "bistable" system,
such as an ammonia (NH3) molecule in which the nitrogen molecule can pop
out of the plane in one direction or the other (representing, say, a 0
or a 1 binary bit), is resistant to noise. Landauer argues that if, furthermore,
the system carefully avoids throwing out any data, by "recycling"
bits, it might be possible to transmit data with no energy loss at all.
Landauer's argument builds on his own work in the 1960s and that of IBM
physicist Charles Bennett who previously suggested that under certain conditions
the computation process itself can proceed without energy dissipation.
(As circuits shrink and speeds increase, the flow of energy and especially
the dissipation of heat will someday become important factors in the design
of new computers.) Although Landauer admits that implementing his proposed
scheme may be impractical, his argument is intended to show that no fundamental
limits of minimum energy expenditure for communication necessarily exist.
(Rolf Landauer, Science, 28 June 1996.)
THE ELECTRICAL RESISTANCE OF A SINGLE XENON ATOM has been measured.
One normally thinks of resistance as the characteristic of a huge number
of atoms (in a wire). But by attaching one or two xenon atoms to the tip
of a scanning tunneling microscope above a nickel surface, physicists at
IBM have shown how conductivity can depend on the quantum state of individual
atoms. The resistance of a one-atom "wire" was measured to be
10**5 ohms while that for two xenon atoms was 10**7 ohms. (Ali Yazdani,
D.M. Eigler, and N.D. Lang, Science, 28 June 1996.)