PHYSICS NEWS UPDATE -- Number 828 June 13, 2007 by Phillip F. Schewe, Ben Stein

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 828 June 13, 2007 by Phillip F. Schewe, Ben Stein
www.aip.org/pnu

TURNING HEAT INTO ELECTRICITY THROUGH SOUND has been demonstrated by
the University of Utah group of physicist Orest Symko. The group
has built devices that can create electricity from the heat that
would otherwise be wasted in objects such as computer chips. The
devices might potentially make extra electricity from the heat of
nuclear power plant towers, or remove extra heat from military
electronics. At last week's meeting of the Acoustical Society of
America in Salt Lake City, five of Symko's students demonstrated the
latest versions of the devices, which they have been developing for
a few years. The devices first convert heat into sound, and then
sound waves into electricity. Typically, each device is a
palm-sized cylinder containing a stack of materials such as plastic
or metal or fiberglass. Applying a heat source, such as a
blowtorch, to one end of the stack creates a movement of air which
then travels down the cylindrical tube. This warm, moving air sets
up a sound wave in the tube, similar to the way in which blowing air
into a flute creates sound. The pitch, or frequency, of the sound
wave depends on the dimensions of the tube; current designs blast
audible sound, but smaller devices would create ultrasound. The
sound wave then strikes a piezoelectric crystal, a commercially
available material that converts sound into electricity when the
sound waves put pressure on the crystal. Symko says a ballpark range
of 10-25% of the heat gets converted into sound in typical
situations. The piezoelectric crystals then convert about 80-90% of
the sound energy into electrical energy. Symko
(orest@xxxxxxxxxxxxxxxx) expects the devices to be used in
real-world applications within two years, and may provide a better
alternative to photovoltaic solar cells in some situations.
(Session 5aPA at meeting; also see University of Utah press release
at http://www.unews.utah.edu/p/?r=053007-1)

POLONIUM IS THE ONLY ELEMENT WITH SIMPLE CUBIC crystal structure,
and new theoretical work explains why that is. In a solid piece of
polonium the atoms sit at the corners of a cubic unit cell and
nowhere else (see figure at http://www.aip.org/png/2007/280.htm).
Many other materials have more crowded structures. For instance, in
a face centered cubic (fcc) structure, atoms (such as potassium,
sodium, iron, and tungsten) sit at the corners of the cube and in
the center of each face. In body centered cubic structure (bdd),
atoms (such as copper, gold, nickel, and iridium) sit at the corners
of the cube and in the very center of the cube. Only polonium has
the simple cubic (SC) structure (see figure at www.aip.org/png).
One reason making the study of Po so difficult is that it is highly
radioactive and spewing forth decay products; indeed, polonium has
more isotopes, 36, than any other element.

Physicists at the Academy of Sciences in the Czech Republic have now
produced the first detailed theoretical explanation for polonium*s
unique crystal structure: it is the result of the complicated set of
orbital energy states of the electrons and their spin energy
states. Such spin-orbit couplings are only made more complicated
interplay of relativistic effects which become important in such
heavy atoms as polonium (element 84). Specifically they have
identified the so-called mass-velocity term (describing the
relativistic increase in mass of electrons traveling with velocities
comparable to the velocity of light) as the cause of the
simple-cubic structure of polonium.

Another polonium oddity: its
elastic anisotropy is greater than for any other solid. That is, it
is about 10 times easier to deform a Po crystal along the direction
diagonal to the consolidated cubic cells than it is to deform the
crystal in a direction perpendicular to any of the cubic faces.
According to Dominik Legut (legut@xxxxxx, 42-0530229-0461), this
property results directly from the simple cubic structure of
polonium. Polonium is a hazardous element that appears in the air
and soil and in such plants as tobacco, tea, and mushrooms. (Legut
et al., Physical Review Letters, upcoming article)

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