Natural Science Forum / Physics / General Physics / January 2007

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 810   30 January 2007 by Phillip F. Schewe, Ben Stein, Turner
Brinton, and Davide Castelvecchi                     www.aip.org/pnu

HEARTBEAT AND BREATHING CYCLES can become synchronized, a new study
shows.  Looking for patterns in the sequence of human heartbeats is
a much studied subject; evidence for pattern-revealing
characteristics such as chaos and fractal or spiral geometry have
been sought.  Breathing, which is more under direct conscious
control than heartbeat, is much less studied. Part of the problem
with searching for a breathing-heartbeat correlation is that these
systems have very different rhythms.  The heart normally beats 60 to
70 times per minute, while the breathing rate is about one-fifth of
that.  Furthermore, the heart and breathing phenomena are complex;
consequently at least for periods of awakeness or rapid-eye-movement
(REM) sleep little or no phase synchrony (that is, breathing and
heartbeat recurring with a consistent relation to each other) can be
found.  However, solid evidence has now been found for a
breathing-heartbeat correlation for periods of deep sleep.
Some signs of phase synchrony have been found before, but only in
small samples of a dozen or so subjects.  By contrast, the study
performed by scientists at Bar-Ilan University (Israel), and the
Martin-Luther University and the Philipps University (both in
Germany), includes 112
healthy subjects of varying ages, men and women, for a variety of
sleep stages.  The researchers conclude, for one thing, that the
breathing rate affects the heart rate but not the other way around.
Both the breathing oscillation and heartbeat oscillation are
disturbed by the kinds of
noise superimposed by higher brain activity present, such as in REM
sleep.   Jan Kantelhardt (jan.kantelhardt@physik.uni-halle.de,
49-345-55254-33) is sure enough of the heart-breathing correlation
that he believes the sleep stages could now be determined by
measuring heartbeat rather than measuring brain waves.  The
researchers are also hoping to establish careful heart-breathing
correlations for patients with heart problems, the better to develop
diagnostic devices.  (Bartsch et al., Physical Review Letters, 26
January 2007; journalists can obtain the text at
www.aip.org/physnews/select )

CHAOS ON A CHIP.  For the first time physicists have shown that well
structured chaos can be initiated in a photonic integrated circuit.
Furthermore, this represents the first time scientists have been
able to study optical chaos at gigahertz rates.
The output of a semiconductor laser is normally regular.  However,
if certain laser parameters are tweaked, such as by modulating the
electric current pumping the laser or by feeding back some of the
laser�s light from an external mirror, the overall laser output will
become chaotic; that is, the laser output will be unpredictable.  To
make the chaos even more dramatic (and exploitable) Mirvais Yousefi
and his colleagues at the Technische Universiteit Eindhoven (in the
Netherlands) use paired lasers, lasers built very close to each
other on a chip in such a way that each affects the operation of the
other.  The Eindhoven chip, using the paired-laser
mutual-perturbation approach to triggering chaos, is the first to
exhibit chaos directly-revealing telltale strange attractors on
plots of laser power at one instant versus laser power at a slightly
later instant-rather than indirectly through recording laser spectra.
Looking ahead to the day when opto-photonic chips are covered with
thousands or millions of lasers, the Eindhoven approach could allow
troubleshooters to pinpoint the whereabouts of misbehaving
lasers---not only that but possibly even exploit localized chaotic
effects to their advantage.
According to Yousefi (m.yousefi@tue.nl) other possible uses for
chip-based chaos will be the business of encryption, tomography, and
possibly even in the establishment of multi-tiered logic protocols,
those based not on just on the binary logic of 1s and 0s but on the
many intensity levels corresponding to the broadband output of the
chaotic laser system. (Yousefi et al., Physical Review Letters, 26
January 2007; text at www.aip.org/physnews/select )

ADDENDUM: In Update 809 we wrote about the gravitational wave
background.  For comparable work in this area we suggest that
interested readers also consult the paper by Easther
(richard.easther@YALE.EDU, 203-432-6959) and Lim in the Journal of
Astroparticle Physics, JCAP04(2006)010 (http://www.iop.org/EJ/jcap/).

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