ROOM TEMPERATURE ICE; small-world networks
Posted on Friday, August 19, 2005 @ 22:20:30 UTC by vlad
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ROOM TEMPERATURE ICE is possible if the water molecules you're freezing are submitted to a high enough electric field. Some physicists had predicted that water could be coaxed into freezing at fields around 10^9 V/m. The fields are thought to trigger the formation of ordered hydrogen bonding needed for crystallization. Now, for the first time, such freezing has been observed, in the lab of Heon Kang at Seoul National University in Korea, at room temperature and at a much lower field than was expected, only 10^6 V/m.
Exploring a new freezing mechanism should lead to additional insights about ice formation in various natural settings, Kang believes (surfion@snu.ac.kr). The field-assisted room-temperature freezing took place in cramped quarters: the water molecules were constrained to the essentially 2-dimensional enclosure between two surfaces: a gold substrate and the gold tip of a scanning tunneling microscope (STM). Nevertheless, the experimental conditions in this case, modest electric field and narrow spatial gap, might occur in nature. Fields of the size of 10^6 V/m are, for example, are thought to exist in thunderclouds, in some tiny rock crevices, and in certain nanometer electrical devices. (Choi et al., Physical Review Letters, 19 August 2005; for another example of seemingly room-temperature ice, see: http://www.aip.org/pnu/1995/split/pnu225-1.htm )
NETWORKING CAN BE CRITICAL, LITERALLY. The theory of "small-world" networks yields insight into innumerable real-world situations, from the Internet to the power grid, from epidemics to opinion making. A small-world network is one where certain nodes, called hubs, have an unusually large number of connections, so that going through hubs one can reach any other node in just a few steps. In real-life small-world networks, researchers have observed "critical" thresholds -- for example, epidemics that spread uncontrollably or spontaneously die out, depending on thresholds in the disease's degree of infectivity or in the number of social contacts individuals have. But network theory has so far been poor at modeling critical thresholds. Now, Joseph Indekeu of Katholieke Universiteit Leuven in Belgium (joseph.indekeu@fys.kuleuven.be) and his colleagues have shown that small-world networks can model critical thresholds if one tunes the hubs to be less influential on their neighbors than the ordinary nodes. For example, a friend's opinion could be more influential in shaping your voting preferences than the opinion of a prominent TV commentator, whose wide audience makes him a hub in the network. The tuning idea, the paper shows, is mathematically equivalent to cutting off most of a hub's connections. The authors also say their results could shed light on, and perhaps help prevent, phenomena such as electrical blackouts and epidemics. The new model even suggests a parallel between networks and general relativity since trading in the interactions between nodes for changes in the network's structure is reminiscent of the gravitational interactions between bodies---gravitational attraction---which can be mimicked by changes in the structure of spacetime---that is, the curvature created by the presence of mass.
(Giuraniuc et al., Physical Review Letters, upcoming article)
Source: PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News Number 742 August 19, 2005 by Phillip F. Schewe, Ben Stein, and Davide Castelvecchi
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