Number 73, March 27, 1992 by Phillip F. Schewe and Ben Stein|
THE CAPACITANCE OF SINGLE QUANTUM DOTS has been measured with a resolution of 1 attofarad (10-18 F). Quantum dots are tiny islands of semiconductors (less than 1 micron on a side) in which confinement in all three spatial dimensions gives rise to interesting quantum effects. Normally, because of their small size and because of the way in which they are made, the dots are usually studied many at a time. But at last week's APS March Meeting in Indianapolis, Raymond Ashoori of AT&T Bell Labs (908-582-7350) described how to study just one. Starting with a 2-dimensional electron gas in a thin layer of gallium arsenide between layers of aluminum gallium arsenide, Ashoori further restricts the movement of electrons in the two lateral directions by applying voltage potentials, which pinch off forbidden areas. The charge in the dot can be monitored to less than a fraction of a single electron charge, permitting a high-resolution capacitance measurement.
A QUICK METHOD FOR PREDICTING HOW MANY PROTEINS FOLD has been developed by researchers at the University of Illinois. It is a relatively straightforward matter to learn the chemical sequences of unfolded proteins, but it takes months with conventional x-ray and NMR techniques to determine a single protein's final three-dimensional shape. At the March Meeting, Peter G. Wolynes (217-333-7385) and his colleagues described a model which allows researchers to take proteins whose shapes are known and predict the shapes of other proteins---having similarities in chemical sequence of as little as 17 percent---using about an hour of supercomputer time. Since a protein's transition from its original unfolded state to its final three-dimensional shape is complicated, with many intermediate states arising from complex interactions between molecules, the Illinois team devised an algorithm in which certain energy states in the protein are favored over others, based on the characteristics of proteins with known shape. According to Wolynes, the predicted shapes can be tested using the conventional methods.
COMETS MAY BE MORE ROCK THAN ICE . A reanalysis of images recorded in the 1980's by the Infrared Astronomical Satellite (IRAS) has turned up large dust streaks (seen only in the infrared) trailing behind many inner-solar-system comets. The amount of dust can add up to a considerable fraction---up to three fourths---of the comet's mass. (Science News, 14 Mar. 1992.)
ASTROLOGY DISCLAIMERS are now carried by 42 newspapers nationwide, according to the Committee for the Scientific Investigation of Claims of the Paranormal (CSIOP), which began a campaign in 1984 to establish such disclaimers. Typical is the notice appearing with the astrology column in the Los Angeles Times: "The astrological forecast should be read for entertainment only." (Skeptical Inquirer, Spring 1992; published by the CSIOP.)