Number 790, August 30, 2006
by Phillip F. Schewe, Ben Stein, and Davide Castelvecchi
Solar System Redefined
Just as in the Bible Adam achieved dominion
over the objects of the earth by naming them, so scientists partly
establish human dominion over the cosmos by naming or classifying
all things animal, vegetable, or mineral.
At a meeting of the
International Astronomical Union (IAU) last week in Prague, the
system of naming planets was revised, and not everyone was pleased.
Hereafter, they declared, there will be eight proper planets and at
least three (and probably lots more) dwarf planets. To be a planet
an object must be orbiting the sun, must be spherical, and must be
big enough to have scarfed up all the matter in its orbital zone.
Pluto, having failed the third of these criteria, is now demoted to
being a dwarf planet, and is joined in that category by two other
objects, Ceres and Xena (whose official name is still 2003UB).
Large-area Sensor Skins and Microphones
Large-area sensor skins and microphones might be possible with
flexible transistors made from cheap ferroelectret packing foam.
Just as in ferromagnetic materials tiny magnetic dipoles become
permanently oriented in the presence of an applied magnetic field,
so in ferroelectric materials electric dipoles become permanently
polarized by the application of an electric field. Ferroelectrets,
a novel class of cheap electroactive materials based on cheap
polymer foams, are often used as packing material and for thermal
insulation.
But now physicists at the Johannes Kepler University
(in Linz, Austria) and Princeton University (US) have shown that
ferroelectret films can muster electric fields big enough to trigger
(switch) a field effect transistor. Hence many of the things
transistors are good for can be engineered using flexible, cheap
ferroelectret materials as building blocks.
Already the researchers
have demonstrated in the lab working versions of flexible
touch-sensors and microphones. Ingrid Graz (ingrid.graz@jku.at)
says that her new form of soft electronics could be useful for
producing flexible paper-thin keyboards and flexible microphones for
mobile phones, active noise control devices, toys, hearing aids, and
surround-sound systems. (Graz et al., Applied Physics Letters, 14
August 2006)
Metallic Water
Metallic Water, an electrically conducting form of water, might
exist under just the right conditions of temperature and pressures
on gas giant planets like Jupiter or ice giants like Neptune. Ice
on Earth comes in many forms---the normal hexagonal ice (manifested
as crystalline ice or as six-sided snowflakes), cubic ice (which is
rare; it can form as tiny crystallites high in the atmosphere), and
other types which vary according to pressure conditions.
A new
theoretical study by physicists at Sandia National Lab shows that a
conducting phase of water could occur at a temperature of 4000 K and
a pressure of 100 gigapascals, which are much more forgiving than
the previous estimates---7000 K and 250 GPa, respectively---and
thought to exist inside Jupiter and Neptune (for a drawing of this
metallic water, see www.aip.org/png ).
Furthermore, the new work
shows, unexpectedly, that on a pressure-vs-temperature phase diagram
the conducting phase of water ice should sit right next to
electrically insulating ice, also called “superionic” ice, since in
that case a water molecule’s two hydrogen atoms are free to move
about while the oxygen atoms remain frozen in place.
According to
Thomas Mattsson (trmatts@sandia.gov, 505-844-9215), one of the
Sandia researchers, one aim of his study of high energy density
water (with densities more than twice the usual 1 g/cm^3 density) is
to better understand the short-lived high-temperature, high-pressure
fluid environment inside Sandia’s Z Machine, the device where huge a
huge portion of electrical charge (stored in capacitor banks
immersed in oil) is sent all at once through wires, producing a huge
batch of soft x rays (see
http://www.aip.org/pnu/2004/split/702-1.html). (Mattsson and
Desjarlais, Physical Review Letters, 7 July 2006)
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