|
Number 389, September 4, 1998 by Phillip F. Schewe and Ben Stein
CHAOS-BASED COMPUTING, a fundamentally new way to perform computations by exploiting the ubiquitous phenomenon of chaos, has been demonstrated in a simulation by researchers in India and the United States (Bill Ditto, Georgia Tech, 404-894-5216). Compared to digital computation, the chaos-based technique might come closer to how the brain performs computation, and might be superior in certain tasks such as pattern recognition. The computer consists of an interconnected grid of "chaotic elements," systems such as ammonia lasers which can generate unpredictable signals even though their behavior is governed by known mathematical equations. To encode specific numbers into each element, the researchers make specific signal patterns correspond to a number and ask each element to open its connection to the rest of the grid when it generates that pattern. Sending its signal out to the grid can trigger activity in neighboring elements. To carry out specific operations such as addition, the researchers connect the elements in a certain way. An unpredictable but deterministic avalanche of activity among the elements ultimately settles down to produce an unvarying signal that corresponds to the desired answer. Having demonstrated their technique in a computer simulation, the researchers are planning to test this idea with chaotic ammonia lasers and hybrid networks of nerve cells and silicon chips. (Sinha and Ditto, Physical Review Letters, 7 September 1998.)
TRIPLE PHOTOIONIZATION OF LITHIUM, a rare process in which a single photon removes all three electrons simultaneously from nature's third-lightest atom, has been detected for the first time by a Japan-US collaboration (Ivan Sellin, University of Tennessee, isellin@utk.edu). Studying this process further promises deep insights into the interactions that can occur between a trio of electrons and therefore a more sophisticated understanding of the interplay between charged particles in many environments such as stars. At the Photon Factory in Japan, an intense beam of extreme-ultraviolet (EUV) photons broadsided a beam of lithium atoms; a detector then recorded the rare process by collecting Li3+ ions. In the most simplified picture of the process, an EUV photon deposits virtually all its energy into a single electron; the electron immediately shares enough energy with the other two so that they could all escape the Li atom. The three-electron interactions are relatively easy to extract from the data since the photon vanishes after striking the atom, and the heavier lithium nucleus acts merely as a sluggish "spectator." Researchers have observed triple photoionization of heavier atoms, such as neon, but such processes are typically more complicated events involving internal rearrangements of other electrons in the atom. (R. Wehlitz et al., Physical Review Letters, 31 August 1998.)
BROWNIAN MOTION IS CHAOTIC. In case one needed any more persuasion that chaos is all around us, a Brussels-Maryland-Utah collaboration has for the first time demonstrated evidence for chaotic behavior in fluids at the microscopic level. The data consists of repeated viewings of a 2.5-micron particle suspended in water. A plot of the particle's position as a function of time is translated into a form which provides information about how the particle's position at one time correlates with the position at a later time. This analysis proved to bear all the hallmarks of chaotic behavior. The chief symptom of chaos is the tendency for particles that initially follow nearby trajectories to diverge quickly from one another. (P. Gaspard et al., Nature, 27 August 1998.)
[an error occurred while processing this directive]
|
