Saturday, 11 August 2012

Physics stuff from the fortnight 30/7 - 12/8/12

Researchers at the Harvard School of Engineering and Applied Sciences have designed a metamaterial with a refractive index of -700.
If that hasn't knocked you off your chair, then read this:
The refractive index of a material determines how quickly electromagnetic radiation propagates through it (the speed of light inside it). That speed will be 'c' (celeritas - 2.996*10^8 ms^-1) divided by the refractive index 'n'.
The refractive index of nothingness would be 1
The refractive index of air is very slightly greater than 1
The refractive index of water is 1.5
This change in refractive index is the reason light refracts, causing the oh-so-famous metaphorical fish to look like it's higher than it really is - light slows down as it enters the water.
Metamaterials (materials engineered to have properties not ordinarily seen) with a negative refractive index, would make the fish look *lower* than it really is.
They would also make light *accelerate* as it entered the fluid (it's obviously not going to be water, any more).
Now consider again -- this metamaterial has a refractive index of -700!!
The researchers achieved this feat via kinetic inductance, where the electrons at the interface between slithers of two semi-conductors - gallium arsenide and aluminium gallium arsenide - were stimulated by microwave radiation (electromagnetic waves at gigahertz frequency).
The semi-conductor slithers were paired and layered up, so that the movement of electrons in the sea of electrons at one end, caused induction in the neighbouring slithers', and the slither next to that's, etc.
In this way, the wave raced along the line, perpendicular to the orientation of the strips, indicating what the researchers described as a "staggering" degree of negative refraction.
The applications for metamaterials like these are diverse - they can be used in just about any situation where maximised precision is necessary - powerful microscopes, optical tweezers, waveguides, etc, etc, etc.

[video] Bobby Llew takes a look around the renewable-powered G24i solar-panel factory, in Cardiff, demonstrating that green power technology doesn't have to be dirty in its manufacture.
Look at his little face, playing with those toys!
G24i produces what they call 'energy harvester' products, which produce small amounts of power, for use in domestic situations.

And, if you like, take a look at 'the' Energy Efficient House, in Berlin, which consumes 5 MWh per year, but produces 16 MWh:

[video] A guided tour of NASA's 'Chamber of Horrrors' at the Environmental Test Engineering and Integration branch of the Goddard Space Flight Center

'Caught on camera: quantum mechanics in action'
Go to the "More Information" link -- lots of pretty graphs!

[video] These animations are freakily convincing! This is the next stage toward making movies without those pesky actors being involved at all....
'Researchers develop new physical face cloning method'

I didn't even know this happened!
'Researchers unlock secret of the rare 'twinned rainbow''
They're not talking about concentric rainbows, where there's a strong rainbow, and a fainter one, slightly further out, which it never touches -- they're talking about a second rainbow which meets at both ends of the first rainbow, but has a flatter arc.
The reason for this effect, they say, is that water droplets deform as they fall - they flatten out into what they call 'burgeroids'. The bigger the droplets, the more they flatten out.
When two rain showers combine, with two distinctly differently-sized sets of droplets, they refract the light with a slightly different angle, creating two arcs, with different heights.

Awesome work -- i shall now look at rainbows with a thousand times as much awe!

Solid State Physics, now:
'Exposing valence-bond model inadequacies'
Europium monoxide (EuO) can exist in two different structures - one like NaCl (sodium chloride), the other like CsCl (caesium chloride).
This is because Europium has variable valency - Eu2+, and Eu3+ - and both states seem to exist interchangeably.
The researchers squeezed the EuO under pressures up to 92 GPa (giga-pascals), to see how it would change in volume, and analysed its structure using XRD (X-Ray Diffraction).
What they found, is that the EuO decreased in volume, as expected, as the pressure was ramped up, but that there was a 7% lurch in volume decrease at 45GPa.
They presumed this would be due to a change in valency, from 2+ to 3+, coincidental with a shift from a NaCl structure to CsCl, which has a higher coordination number, longer bond length, and smaller ionic size, but they found that the valency did not change this way.
The researchers found that there was a transition phase, from 14 to 44 GPa, with an increasing proportion of 2+ to 3+ valency Europium ions, as the pressure increased.
Here, at 45 GPa, is where the 7% volume drop occurred, and a shift back to 2+ ions. From 45 to 59 GPa, the NaCl and CsCl-like structures coexisted; and above 59 GPa, the CsCl structure existed with 2+ ions throughout.
Fascinating, huh?
"Europium monoxide may not be found in the typical household today, but that may soon change. Because of its properties as a spin-polarized ferromagnetic semiconductor, much research is being directed toward manufacturing EuO spintronic devices. Spintronics is the emerging technological field that has already given us high-capacity computer hard drives based on the giant magnetoresistance effect."

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