Number 58, December 5, 1991 by Phillip F. Schewe and Ben Stein|
PERSISTENT CURRENTS , currents that do not decay, have long been known to exist in superconductors. In 1990 scientists at AT&T Bell Labs showed that persistent currents could also exist in normal metal rings of sufficiently small size, verifying a prediction made in 1983. In particular they measured the magnetization of an ensemble of 107 copper rings, each only 0.5 microns in diameter. Now a group at the IBM Watson Research Center has measured the magnetic response of single, isolated (micron-sized) gold loops (V. Chandrasekhar et al., Physical Review Letters, 16 December 1991). The current in the loops was found to oscillate with a period proportional to the magnetic flux threading the loops, as expected, but the size of the current was larger than expected by a factor of from one to two orders of magnitude.
A BOW SHOCK AND TAIL associated with a supergiant star (IRS7) near the center of our galaxy have been discovered by astronomers using the Very Large Array radio telescope. Like the solar wind that buffets the earth, a wind of particles arising from the core of the Milky Way seems to be streaming past IRS7. Farhad Yasef-Zadeh of Northwestern University and Fulvio Melia of the University of Arizona, who made the observations, believe the source of the wind is not coincident with the very center of the galaxy, but with a star cluster nearby. (New Scientist, 23 November 1991.)
EVIDENCE FOR CLUSTER IMPACT FUSION swings back and forth. This phenomenon, in which the rate for deuterium-deuterium fusion would be enhanced by many orders of magnitude if a beam of clusters of D2O molecules (rather than free deuterons) were collided with a deuterated target, was first reported by a Brookhaven team in 1989. A new experiment carried out at the University of Washington in Seattle finds no evidence for cluster impact fusion, at least not for small water clusters such as OD-, O2D3-, and O3D5-. (R. Vandenbosch et al., Physical Review Letters, 16 December 1991.)
SONOCHEMISTRY AND AMORPHOUS IRON are two of the things possible with sonoluminescence, a phenomenon in which ultrasonic sound waves passing through a liquid cause bubbles to rapidly form and then collapse, emitting visible light. This "cavitation" process whereby sound energy is converted into concentrated light energy is still poorly understood, yet it is being put to practical use. The high temperatures (5000 K) and high pressures (500 atm.) arising from cavitation can be used to accelerate chemical reactions. Furthermore, Kenneth Suslick of the University of Illinois has used cavitation to create an amorphous iron powder; the bubbles first liberate the iron atoms from a molecular solution and then quickly freeze the iron before it can form into a crystal. The cooling rate was estimated to be more than the 105 to 107 K/sec rates normally needed in making other metallic glasses. Amorphous iron may have commercial applications in the sound-recording industry. (Physics Today, November 1991.)