Number 856, February 13 , 2008
by Phillip F.Schewe and Jason S. Bardi www.aip.org/pnu
A new experiment at Colorado State University studies the chaotic dynamics of "flux drops"-microscopic swirling eddies of supercurrent-that flow along a narrow channel crossing a superconducting strip. An applied current perpendicular to the channel causes a flux drop to nucleate, grow, and break off at the end of the channel. The drop is then driven along the channel by the current.
This process is reminiscent of water drops dripping from a nozzle, for a long time of the chief methods for understanding chaos. The Colorado State investigators used a micron-sized magnetic sensor to directly detect the magnetic field of individual drops as they passed beneath it. The resulting time sequence of flux drops, just like that of water drops from a faucet, exhibits clear signatures of deterministic chaos, implying that the irregular-looking sequence of drops is not random, but predictable from knowledge of earlier drop times.
However, predicting the sequence more than 4 or 5 drops into the future becomes exponentially difficult-another hallmark of chaos. According to Stuart Field (firstname.lastname@example.org, 970-491-3773) this is the first conclusive observation of chaotic behavior in moving flux structures. The direct observation of the time series allows for an unambiguous identification of chaos in this system. (Field and Stan, Physical Review Letters)
Anti-Hydrogen Atoms Detected in a Penning-IOFFE Trap
The Antiproton Trap Collaboration (ATRAP) working at CERN has succeeded in detecting, for the first time, the presence of anti-hydrogen atoms (each made of a positron and an anti-proton) in the heart of a combined Penning-Ioffe trap. Both types of trap combine electric and magnetic fields to hold charged particles and neutral particles with magnetic moments. Both traps play an important role: the Penning trap is needed to hold and control the positrons and antiprotons enough so that they can join into the antimatter counterpart of hydrogen atoms, while the Ioffe trap is needed to trap those atoms once they’re made, in order to carry out high-precision spectroscopic studies.
Producing and then cooling anti-protons (created in powerful collisions at energies of billion of electron volts and then slowed in stages to energies of milli- or micro-eV) is hard to do in the first place, much less combining them with positrons from a radioactive source. Some scientists feared that it might be impossible to hold the positrons and antiprotons long enough to produce anti-atoms when a Ioffe for neutral atoms was in place, but this new development dispels that worry. Gerald Gabrielse, head of the ATRAP team (<http://hussle.harvard.edu/~atrap/>) says that they do not yet have evidence of trapped anti-atoms, only that anti-atoms are being produced; indeed the number of anti-atoms actually goes up when the Ioffe trap is turned on. (Gabrielse et al., Physical Review Letters)
The American Institute of Physics Science Writing Awards have been named
There are four categories of writing: journalist, scientist, broadcast, and books intended for children. Tim Folger wins the 2007 science writing award for a journalist for his Discover Magazine article, "If an Electron can be in Two Places at Once, Why Can’t You?" James Trefil wins the 2007 scientist award for his Astronomy Magazine article, "Where is the Universe Heading?" Jacob Berkowitz wins the award in the children’s category for his book "Jurassic Poop," which was published by Kids Can Press. And the broadcast award goes to repeat winners Bob McDonald, Pat Senson, and Jim Handman for "Multiple Worlds, Parallel Universes," which aired on the CBC Radio show Quirks & Quarks.