Leidenfrost effects..Entangled photon holes..Sunlight and Chips

[Guest guest]

LIQUID FLOWING UPHILL; MIGHT BE USED TO COOL CHIPS. In a phenomenon

known as the " Leidenfrost effect, " water droplets can perform a

dance in which they glide in random directions on a cushion of vapor

that forms between the droplets and a hot surface. Now, a

US-Australia collaboration (Heiner Linke, University of Oregon,

linke) shows that these droplets can be steered in a

selected direction by placing them on a sawtooth-shaped surface.

Heating the surface to temperatures above the boiling point of water

creates a cushion of vapor on which the droplet floats. The

researchers think that the jagged sawtooth surface, acting as a sort

of ratchet, redirects the flow of vapor, creating a force that moves

the droplet in a preferred direction. The droplets travel rapidly

over distances of up to a meter and can even be made to move up

inclines. This striking method for pumping a liquid occurs for many

different liquids (including nitrogen, acetone, methanol, ethanol

and water) over a wide temperature range (from - 196 to + 151 C).

A practical application of this phenomenon might be to cool off hot

computer processors. In a concept the researchers plan to test,

waste heat in a computer would activate a pump moving a stream of

liquid past the processor to cool it off. Such a pump for coolants

would need no additional power, have no moving parts, and would

spring into action only when needed, when the processor gets warm.

(Linke et al., Physical Review Letters, upcoming; extensive visuals

and explanations at http://www.uoregon.edu/~linke/dropletmovies/ )

 

ENTANGLED PHOTON HOLES. In some semiconductor devices, such as

light-emitting diodes, an applied voltage can dislodge electrons

from some atoms, leaving behind a hole which behaves in some

situations as if it were a positively charged particle in its own

right. A " current " of holes can move through the material and the

holes can recombine later with electrons to produce light. In very

loose analogy, James Franson (Johns Hopkins) suggests that photonic

holes might be created; a photon hole, to give one example, would be

a place in an otherwise intense laser-beam wavefront where a photon

had been removed (by passing the laser beam through vapor, for

instance). Not only can there be photon holes, Franson

(443-778-6226, james.franson) suggests, but the holes can

be entangled, meaning that their quantum properties would be

correlated, even if far apart from each other. Such entangled

photon-holes would be able to propagate through optical fibers just

as well as entangled photons, but might be even more robust against

the decoherence (the undoing of the quantum correlations) that

plagues present efforts to establish quantum information schemes.

Franson expects to do put his idea to experimental test in the next

few months. (Physical Review Letters, 10 March 2006)

 

SUNLIGHT ON A CHIP. A new LED design employs a handy combination of

light and phosphors to produce light whose color spectrum is not so

different from that of sunlight. Light emitting diodes (LEDs)

convert electricity into light very efficiently, and are

increasingly the preferred design for niche applications like

traffic and automobile brake lights. To really make an impression

in the lighting world, however, a device must be able to produce

room light. And to do this one needs a softer, whiter, more color

balanced illumination. The advent of blue-light LEDs, used in

conjunction with red and green LEDs, helped a lot. But producing

LED light efficiently at blue, red, and yellow wavelengths is still

relatively expensive, and an alternative approach is to use

phosphors to artificially achieve the desired balance, by turning

blue into yellow light. Scientists at the National Institute for

Materials Science and at the Sharp Corporation (in Japan) have now

achieved a highly efficient, tunable white light with an improved

yellow-producing phosphor (see figure at

http://www.aip.org/png/2006/257.htm ). Their light yield is 55

lumens per watt, about twice as bright as commercially available

products operating in the same degree of whiteness. (Xie et al.,

Applied Physics Letters, 6 March 2006; contact Rong-Jun Xie,

xie.rong-jun)

 

lox and bagels and links and locks..a physist's dream!

........bob

postscriptum: wonder if Sunlight and Chips is fattening?..bn