Physics News Update 810

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Number 810, January 30, 2007 by Phil Schewe, Ben Stein, and Davide Castelvecchi

Heartbeat and Breathing Synchronicity

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, 2 February 2007
Contact Jan Kantelhardt
Martin-Luther-Universität Halle-Wittenberg jan.kantelhardt@physik.uni-halle.de
+49-345-55254-33

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
Contact Mirvais Yousefi
Technische Universiteit Eindhoven
m.yousefi@tue.nl

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