Physics tip sheet #41 - April 5, 2004

The smallest diameter carbon nanotubes yet have been discovered by a collaboration of researchers from Japan and Germany. At 3 angstroms across, the tubes are smaller than previously believed possible from some theoretical calculations. The researchers found the nanotubes at the center of multi-walled carbon nanotubes formed in a hydrogen arc discharge, and produced images of them with high-resolution transmission electron microscopy. According to the researchers' calculations, the record-setting nanotubes are likely capped at each end by cages formed of twelve carbon atoms. Prior to the recent discovery, 4 angstrom carbon nanotubes capped with twenty-atom cages were generally thought to be the smallest diameter configuration to be stable.

2) Superlensing in Liquid Waves
Physical Review E (March)
X. Hu et al.
http://link.aps.org/abstract/PRE/v69/e030201

Negative refraction, in which waves bend opposite to the usual direction as they pass from one medium to another, attracted a lot of attention when it was demonstrated for electromagnetic waves in so-called left handed materials. The effect has now been observed in liquid surface waves. The authors of this paper placed an array of copper cylinders in a tank of liquid. A source generated waves on one side of the cylinders, and the researchers observed the pattern of waves on the opposite side. At certain wave frequencies, negative refraction caused the waves to form an image of the source on the far side of the cylinders. In addition to observing this "superlensing" effect, the researchers found a band gap, a range of frequencies of waves that won't propagate through the cylinders.

3) Novel High-Density Water Discovered
S. Engemann et al.
Physical Review Letters (to appear) A new form of high-density water that forms at the interface between water ice and silicon dioxide has been discovered by researchers at the Max Planck Institute for Metals Research in Stuttgart. Because the earth's crust is primarily composed of silicon dioxide, the discovery may be important for understanding the motions of glaciers, the stability of permafrost, and other phenomena involving contact between ice and earth. The researchers discovered the high density water layer, which is as much as 17% more dense than normal water, with a new type of x-ray imaging scheme that made use of the brilliant, high-energy x-ray beams provided by the European Synchrotron Radiation Facility in Grenoble, France.

4) Adaptation and Enslavement in Symbiosis
M. R. Frean and E. R. Abraham.
Physical Review E (to appear)

Rapid adaptation may have disadvantages in symbiotic relationships among creatures from different species. Researchers at New Zealand's Victoria University and National Institute of Water and Atmospheric Research have produced a model that suggests rapidly evolving members of symbiotic relationships become highly cooperative over time, while slowly evolving members give little in return. The result is in contrast to so-called tit-for-tat models of cooperation among creatures of a given species, which tend to contribute to their relationships comparably. The new model may help explain the existence of relationships, often observed in nature, involving a host that benefits from symbiotic partners who seem to gain little or nothing in return. Examples of these unequal partnerships include nitrogen-fixing bacteria in legumes, and bioluminescent bacteria in squids and fish, among others.

5) Traffic jams in "model ketchup"
Physical Review Letters (to appear)
M.D. Haw

As a simple model of everyday jamming phenomena such as ketchup or toothpaste that gets stuck in a tube, researchers have studied a suspension of plastic beads in a liquid being sucked through a narrow tube. The researchers varied the size and concentration of the plastic beads, and found that if the proportion of beads exceeds a critical amount, the suspension jams; otherwise it flows freely. Jamming takes place even though the tube is many times wider than the beads, an effect the author likens to "a traffic jam on a 500-lane highway." The system also displays a "self-filtering" effect-- the concentration of beads decreases after the suspension is sucked through the tube. Better understanding of jamming could be important for many industrial applications, from getting grain out of farm silos to getting ketchup into bottles.

Journal articles are available to journalists on request.