Number 80, May 19, 1992 by Phillip F. Schewe and Ben Stein
WHERE DOES THE TIGER GET ITS STRIPES? For decades, scientists in a wide range of disciplines have strived to understand how nature generates biological patterns such as the stripes on a tiger and the rings on bees. In 1952, mathematician Alan Turing stimulated much interest in this question when he proposed that stationary patterns can be formed in chemical reactions that are mediated by diffusion processes. However, experimenters were unable to reproduce "Turing patterns" in the laboratory until last year, when Qi Ouyang and Harry Swinney at the University of Texas demonstrated 2-dimensional hexagonal arrays which resemble chicken skin. Produced by a chlorite-iodide-malonic acid (CIMA) solution which diffuses through glass disks and reacts on a gel surface, these patterns spontaneously disappear and then reappear when the system passes through a critical temperature known as the Turing bifurcation point. At the recent APS meeting in Washington, D.C., Ouyang reported how the adjustment of a single chemical component in a gel solution could result in identifiable, stationary, striped or dot patterns. Swinney admits that the demonstration of such chemical patterns does not yet prove that the Turing mechanism is responsible for biological patterns. (Science News, 9 May 1992.)
BINARY OPTICS is a new technology that has already led to thinner, lighter lenses and optical devices that were once impossible to make. The method for manufacturing binary optics devices explains the technology's name: workers use the same equipment that fabricates digital circuits to etch patterns onto optical materials. Whereas conventional lenses, using the principle of refraction, require several millimeters of material, binary optics, employing diffractive effects accomplished in a space only a fraction of a wavelength in size, can facilitate devices with surface dimensions as small as half a micron and depths as shallow as a nanometer. The etched patterns, usually made up of microscopic staircases, are designed to break up the incident light into individual wavefronts, which interfere in such a way as to create a new wavefront that travels in a desired direction. Virtually any optical transformation can be achieved with binary optics: for example, workers at Hughes converted circular patterns into straight lines, a geometry that is much easier for pattern-recognition machines to decipher. The production method offers another advantage: optical components can now be etched directly onto integrated circuits. This makes it feasible to produce systems that mimic biological vision, with light-gathering devices on top of individual processing elements. (Scientific American, May 1992.)
PHYSICS BACHELOR'S DEGREE recipients, perhaps in response to the current economic recession, are going on to graduate school in greater numbers rather than taking up immediate employment. Of the 5145 physics/astronomy bachelors for the class of 1991, 35% sought a job, 37% went into physics-related graduate study, and 20% into other graduate study. Other facts contained in a new AIP report entitled 1990-91 Survey of Physics and Astronomy Bachelor's Degree Recipients: 17% were women, 6% were non-U.S. citizens, 2% were black, 2% were Hispanic Americans, and 5% were Asian Americans. (For more information contact Susanne Ellis, AIP, 212-661-9260.)
|
