Physics News Update, Number 486

Number 486, May 26, 2000 by Phillip F. Schewe and Ben Stein

FREELY ROTATING MAGNETIC PARTICLES in a new nanocomposite material might lead to a new kind of transformer. Transformers, which convert power from one voltage to another, are present at all levels of the electrical distribution grid. Usually made from metal (iron cores and copper windings), transformers regularly lose energy through wasteful eddy currents which form when current is switched from one state to another.

A research team led by Ron Ziolo (RZiolo@compuserve.com) and Javier Tejada at the University of Barcelona Xerox Lab in Spain might be able to mitigate this problem by making tiny transformers which do not suffer eddy currents. They have developed a composite material consisting of 5 to 10-nm magnetic iron-oxide particles lodged in a polymer matrix. When a magnetic field is turned on, the particles break free just enough to carve out some elbow room in their immediate vicinity. Although they do not move through the matrix, they are free to rotate and they proceed to line up with the fields.

This nanocomposite material consists of tiny magnetic particles dispersed in a lightweight, insulating polymer solid. Other than serving as a lossless transformer, the nanomagnets could act as miniature switches or sensors in smart materials, or as a form of microwave shielding. Also, the material is expected to have novel acoustic, thermal, and optical properties. (Tejada et al., Journal of Applied Physics, June 1, 2000; Select Article.)

ATOM CHIPS. Last year scientists at the University of Innsbruck in Austria succeeded in guiding neutral atoms along the outside of current-carrying wires (Update 416); the atoms were trapped and manipulated by magnetic fields generated by the current in the wire. Now the same scientists have, through a deft series of steps involving extra current-carrying coils and laser beams, been able to herd cold lithium atoms to within a few microns of a patterned microchip, where the atoms come under the control and guidance of currents in the chip.

The goal of the Innsbruck physicists (Joerg Schmiedmayer, joerg.schmiedmayer@uibk.ac.at, 011-43-512-507-6306) is to develop an integrated circuit for atoms and eventually (when the source of the atoms is not a mere atom beam but a true Bose-Einstein condensate) for atom waves. Such a device might be of service for doing quantum optics or computation involving quantum entanglement. (Foman et al., Physical Review Letters, 15 May 2000; Select Article.)

ATOMOSPHERIC GAMMA RAYS. As if thunderstorms don't do enough by sending buckets or rain and thunderbolts to the ground, they are now known to produce gamma radiation with energies up to 10 MeV. Physicists at the University of Bologna in Italy have observed two kinds of gammas in their scintillation detectors: lower-energy gammas (less than 3 MeV) from radioactive aerosol particles descending in rainfall and higher-energy gammas (up to 10 MeV). Previously researchers had seen photons with energies only up to hundreds of keV, and only then by using detectors mounted in planes or on balloons.

The Bologna results (Menotti Galli, menotti.galli@bo.infn.it) were recorded on a mountain at Gran Sasso, where interesting physics experiments are also going on underground (WIMP detectors; see Update 472). The more potent gammas are most likely emitted by electrons in the atmosphere coming to rest after having been accelerated to high velocities by electric fields associated with lightning. A similar mechanism is thought to be responsible for other weird atmospheric emissions such as "red sprites" and "blue jets." (Brunetti et al., Geophysical Research Letters, 1 June 2000.)