Physics Tip Sheet #69, June 28, 2007
American Physical Society
Highlights in this Issue: the first heat transistor, remote controlled nanomachines, high performance energy storage, and the physics of crash landing on sand.
The First Heat Transistor
J. Pekola et al.
Remotely controlled nanomachines
M. J. Comstock et al.
Physicists at the
Scientists have experimented with shape-shifting azobenzene in previous studies, but the molecules only responded properly when suspended in liquids or incorporated into plastics, neither of which makes a very good foundation for complex nanomachines. In order to get the molecular machines to function while mounted on a gold surface, the physicists first had to add legs built of carbon and hydrogen atoms to hold the molecules slightly away from the metal. Although the legs anchoring the molecules to the surface only provided a fraction of a nanometer of clearance (less than a billionth of a meter), it was enough to allow the molecules to move in response to the UV illumination.
The team confirmed their achievement with a series of scanning tunneling microscope images showing that they could switch the molecules' shapes from one configuration and back again. - JR
High-performance energy storage
Vivek Ranjan et al.
North Carolina State University physicists have recently deduced a way to improve high-energy-density capacitors so that they can store up to seven times as much energy per unit volume than the common capacitor. High performance capacitors would enable hybrid and electric cars with much greater acceleration, better and faster steering of rockets and spacecraft, better regeneration of electricity when using brakes in electric cars, and improved lasers, among many other electrical applications.
Air pressure matters when landing on sandy planets
G. Caballero et al.
A steel ball dropped into loose, fine sand makes an impressive splash, according to physicists of the Physics of Fluids group investigating the fluid-like properties of sand at the University of Twente in the Netherlands. Such considerations factor into designing a rover to land on and move about Martian dunes or other dusty surfaces.
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