Number 252, December 18, 1995 by Phillip F. Schewe and Ben Stein INTERPLANETARY DUST PARTICLES (IDPs) are deposited on the Earth at the rate of about 10,000 tons per year. Does this have any effect on climate? Scientists at Caltech have found that ancient samples of helium-3 (coming mostly from IDPs) in oceanic sediments exhibit a 100,000- year periodicity. The researchers assert that their data, taken along the Mid-Atlantic Ridge, support a recently enunciated idea that Earth's orbital inclination varies with a 100-kyr period; this notion in turn had been broached as an explanation for a similar periodicity in the succession of ice ages. (K.A. Farley and D.B. Patterson, Nature, 7 December 1995.) DO GLUEBALLS EXIST? In quantum chromodynamics (QCD), the theory of the strong interaction, the force between quarks is carried by gluons, just as the electromagnetic force between electric charges is carried by photons. Since gluons have a "color charge" (analogous to electric charge) they can bind to each other as well as to quarks. However, telling such gluon states, or glueballs, from other particles is sticky. Some physicists approach the problem by inventing an Erector-Set world in which quarks sit at discrete sites in a cubic lattice. Work in this area is computer-intensive since the interactions of many particles over the interstices of a fine grid (the finer the better) must be followed through myriad iterations. In what they call "the largest single numerical calculation in the history of computing," three IBM physicists have now derived the mass of what should be the lightest glueball. Their value, 1707 MeV, is very close to that of an already-observed particle, f(1710). (J. Sexton et al., Physical Review Letters, 18 December 1995.) THE EDITORSHIP OF THE JOURNAL NATURE passes this week from one physicist to another. John Maddox, editor during the periods 1966-73 and 1980-95, is now succeeded by Philip Campbell, most recently editor of Physics World magazine. In his final issue, Maddox weighs in as an author of an extensive article on science in China. (Nature, 7 Dec.) MICROMACHINED ULTRASONIC TRANSDUCERS have been built which can emit and receive airborne ultrasound at frequencies above 10 MHz, much higher than current ultrasonic transducers which operate at about 50 KHz. Igal Ladabaum of Stanford University (igal@macro.stanford.edu) presented a paper on the new transducers at last month's Acoustical Society of America meeting in St. Louis. Although bats use airborne ultrasound with great success, humans have found it difficult to work with because it attenuates (weakens) rapidly. In order for the new transducers to resonate at high ultrasonic frequencies, they must be much smaller than today's piezo-electric ceramic and electrostatic transducers which operate only at low ultrasonic frequencies. The high-frequency transducers are made up of hundreds of tiny drumheads, each about as wide as a human hair (25 microns) and 100 times thinner than a piece of paper. They vibrate when hit with ultrasound and produce a measurable electrical signal. Conversely, an electrical impulse applied to the drumheads causes them to vibrate, producing ultrasound. Applications for the new transducers include flow sensing, sensitive imaging to evaluate pipelines and structures without destroying them, and more accurate position sensing for robotics. The mass-produced transducers can also be applied to existing fluid ultrasound technologies, such as medical imaging, to provide less expensive equipment. [an error occurred while processing this directive]