Number 293, October 30, 1996 by Phillip F. Schewe and Ben Stein
SIGNAL TRANSMISSION THROUGH A MAMMALIAN NERVE-CELL NETWORK can be enhanced
with the help of electrical noise, a new experiment has shown. First proposed
to explain the periodicity of ancient ice ages (in which the random "noise"
of climate variations may have augmented the effects of predictable Earth-Sun
distance variations from year to year) and first experimentally demonstrated
in lasers (in which the direction of laser light traveling around a loop
was switched from clockwise to counterclockwise by adding acoustical noise
to the crystal from which the light emerged), the phenomenon of "stochastic
resonance" (SR) describes how introducing a certain amount of noise
into a system can actually enhance the transmission or detection of a weak
signal so as to maximize the ratio of signal to noise. In the first demonstration
of SR in mammalian tissue, researchers (Mark Spano, Naval Surface Warfare
Center, 301-227-4466) apply a weak electric signal (containing both signal
and noise) to a slice of rat hippocampus, a brain region essential for
memory and other tasks. With the slice parallel to the plane in which nerve
cells convert incoming signals into electrical nerve impulses, the researchers
could transmit a weak signal to all nerve cells in the network. At an optimal
noise intensity a maximum in the signal-to-noise ratio was reached--a hallmark
of SR. This experiment offers the intriguing possibility that SR may potentially
be exploited to aid transmission, detection and processing of signals in
neuronal networks. (B.J. Gluckman et al., Physical Review Letters, 4 November
1996.)
A QUANTUM COMPUTER COULD TOLERATE ERRORS while carrying out calculations,
researchers at Los Alamos have now shown. Computers that operated according
to the rules of quantum mechanics have the potential to perform powerful
tasks (such as factoring huge numbers) because of their radically different
approach to logic: unlike a conventional computer's bits, which exist either
as a 0 or a 1, a quantum bit (or "qubit") could not only exist
simultaneously as a 0 and a 1 but could interact with other qubits so that
its properties became "entangled" with those of the other qubits.
Yet some physicists argue quantum computers may be impossible to achieve
on a practical level because the slightest amount of noise would destroy
the entanglement and thus corrupt the state of the qubits. Up to now, proposed
"quantum error correction" schemes have shown merely how to preserve
the state of qubits. Now, Los Alamos researchers (Raymond Laflamme, 505-665-3394)
have developed an algorithm for carrying out reliable calculations on a
"qubyte" made of 7 entangled qubits while accounting for the
possibility that one of the qubits is corrupt (upcoming paper in Phys Rev
Lett). Experimentally, quantum computing is regarded as a long-term possibility:
although quantum versions of logic gates have been constructed (see Update
#250), researchers are still working to entangle more than two quantum
systems at a time.
A PHOTOELECTROCHROMIC (PEC) cell harnesses a photochromic layer, which
changes color by absorbing light, with an electrochromic layer, which changes
color under the influence of an electric field, to make a self-powered
smart window. On a sunny day the one layer supplies the photovoltage needed
by the other layer to darken the window, letting in less light and thus
lowering air- conditioning costs. This photoelectrochromic process, developed
by scientists at the National Renewable Energy Lab in Golden, Colorado,
might also be useful in display applications. (C. Bechinger et al., Nature,
17 October 1996.)
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