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MIT Researchers Develop Sensitive Technique to Detect Chaos in Data

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CAMBRIDGE, Mass.--MIT researchers have developed a technique that could mean chaos for many scientists.

In every field from microbiology to astronomy, researchers get erratic data; strange results that don't fit established patterns. Are those data simply "noise"--random, unpredictable signals that are best ignored--or do they actually follow a subtle structure?

That there is order behind seeming disorder is the essence of chaos, a phenomenon that has been found in many areas of science, from the weather (as established by Professor Emeritus Edward N. Lorenz of MIT's Department of Earth, Atmospheric, and Planetary Sciences) to the orbits of asteroids (as established by Professor Jack Wisdom of the same department).

Knowing that chaos exists in a system helps scientists learn more about that system. "Finding chaos in a system implies that there is a structure behind that system. And that's something you want to know," said Dr. Chi-Sang Poon, a principal research scientist in the Harvard-MIT Division of Health Sciences and Technology. In addition, understanding the chaotic pattern could in some cases allow scientists to control the phenomenon.

But first chaos must be detected, and that is quite difficult. "There's a very fine line between chaos and noise," Dr. Poon said. A new mathematical technique developed by Dr. Poon and Mauricio Barahona, a graduate student in physics, may simplify the process.

The technique, which the scientists describe in the May 16 issue of Nature, is much more sensitive than others in telling chaos from noise. It also requires an order of magnitude fewer data points, which means that many more scientists will now be able to analyze their data for chaos.

Dr. Poon has already received excited queries to that end from a biomedical scientist and a climatologist. "Both have relatively small data sets because their data are difficult to get, so none of the existing methods would work in their cases," Dr. Poon said. "Tens of thousands of data points are needed for other techniques," he explained. "We can determine with very high probability if there's chaos in a data set with just a few hundred data points."

The new technique grew out of an assignment Dr. Poon gave his class in 1993. "I had an idea for a way to detect chaos, but I hadn't tested it yet," he explained. Several students did a good job on the assignment, but "Mauricio [Barahona] did a terrific job," Dr. Poon said. Mr. Barahona proceeded to extend the study, while at the same time working toward his PhD in physics (he received his degree June 7). His thesis is unrelated to the work reported in Nature.

Dr. Poon notes that the new technique, which is a mathematical procedure, is adapted from earlier work by the late Norbert Wiener. Professor Wiener, a member of the MIT faculty for 45 years, was a genius who among other things founded the field of cybernetics. (Dr. Poon named one of his computer network nodes "cybernet" in honor of Professor Wiener.)

In continuing work, Dr. Poon is fine-tuning the technique and working with other colleagues in applying it to heart disease. The human heartbeat is thought to be a chaotic system, Dr. Poon explained. Its irregular rhythm "is actually a symbol of health," he said. With congestive heart failure, for example, "the heartbeat is seen to get more and more regular."

So "our long-term hope is to use our technique as a diagnostic tool for heart disease by detecting changes in the chaotic system," he said. He is collaborating on the current work with Roger G. Mark, the Grover M. Hermann Professor of Health Sciences and Technology, and Professor Richard J. Cohen, both of the Harvard-MIT Division of Health Sciences and Technology. Christopher K. Merrill, who graduated from the Department of Electrical Engineering and Computer Science June 7, is also involved. Mr. Merrill began the research through the Undergraduate Research Opportunities Program.

The work is supported by the NSF, the ONR, the National Heart, Lung, and Blood Institute, and a Spanish MEC-Fulbright Fellowship. Dr. Poon has applied for a patent on the technique.

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