Public Release: 

Physics Tip Sheet #16 - June 5, 2002

American Physical Society

1) Water lubricates well because it expands when frozen
E. A. Jagla
Physical Review Letters (Print issue: June 17, 2002)

Water continues to astound with its unusual properties. Now the fact that water expands as it freezes, unlike most fluids, seems to be responsible for why it is such a good lubricant. The good lubrication is essentially because water avoids solidifying as it is squeezed, a process analogous to the melting of ice. This result gives hints on how to create good lubricants, especially for micromechanical devices.

Journal article:

2) A beaker without walls
P. Ayotte, R. S. Smith, G. Teeter, Z. Dohnálek, G. A. Kimmel, B. D. Kay
Physical Review Letters (Print issue: June 17, 2002)

Researchers have created a super-cooled fluid that holds its shape like a solid and is more than 1000 times more viscous than honey. Mixtures of fluids trapped in this state show unusual properties.

Physical Review Focus:
Journal article:

3) Quantum-optical catalysis
A. I. Lvovsky, J. Mlynek
Physical Review Letters (Print issue: June 24, 2002)

One of the simplest optical devices is a beamsplitter. It splits a beam of light into two parts going in different directions and can be made simply from a half-silvered piece of glass. However, the beamsplitter also has fundamentally quantum behavior. A single photon passing through a beamsplitter can make quantum changes to other light passing through the beamsplitter while remaining unaffected itself, a kind of catalysis. Such a process has now been experimentally demonstrated and forms the first of two stages required to perform quantum computing using classical optical elements.

Journal article:

4) Charm school for quarks
SELEX collaboration
Fermilab seminar

Of the six flavors of quarks, just two (up and down) make up most of normal matter. However, new particles containing two charm quarks and either an up or down quark have been observed in the SELEX experiments. The three-charm particle remains elusive.

Physics News Update:
SELEX project:

5) Rotational drag on DNA
P. Thomen, U. Bockelmann, F. Heslot
Physical Review Letters (Print issue: June 17, 2002)

DNA molecules often rotate in biomolecular processes, from DNA denaturation to enzyme translocation. As such, many biomolecular models incorporate some sort of rotational friction force, although there has been debate over its magnitude. This force has now been measured while unzipping a DNA molecule by pulling the two strands apart. As the strands separate, the free end rotates, just as pulling apart the strands of a rope causes it to twist. The rotational drag of a DNA molecule turns out to be about ten times as much as for a straight rod of comparable size.

Journal article:

6) Electrons surf on sound waves
A. Aharony, O. Entin-Wohlman
Physical Review B (Print issue: June 15, 2002)

Applying surface acoustic waves to a conductor can push electrons along, creating a quantized current. The current is quantized because a specific number of electrons "ride" each acoustic wave. A new model describes how this can work in realistic conductors and qualitatively predicts all features of this phenomenon that have been observed experimentally.

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7) Molecular BEC behavior and "Bosenova" explained
M. Mackie, K. Suominen, J. Javanainen
arXiv preprint server

Recent observations of atom-molecule coherence in Bose-Einstein condensates have employed Feshbach resonant interactions. However, the experiments showed unexplained phenomena including losses of condensate atoms and collapsing condensates or "Bosenovas". A new model of the process implicates rogue molecular dissociation to noncondensate atom pairs as the physical mechanism behind the unexplained observations.



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