Number 742, August 19, 2005
by Phil Schewe, Ben Stein, and Davide Castelvecchi
Room-Temperature Ice in Electric Fields
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 109 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 106
Exploring a new freezing mechanism should lead to additional
insights about ice formation in various natural settings, Kang
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 106 V/m are, for example, are
thought to exist in thunderclouds, in some tiny rock crevices, and
in certain nanometer electrical devices.
(Choiet al., Physical
Review Letters, 19 August 2005;
for another example of seemingly room-temperature ice, see
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.
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 (firstname.lastname@example.org) 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
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)