Friday, October 8, 2010

First frictionless superfluid created from molecules

Some fluids have no friction (Image: Don Farral/Getty)Kate McAlpine - CHILL them enough and some atoms creep up walls or stay still while the bowl they sit in rotates, thanks to a quantum effect called superfluidity. Now molecules have got in on the act.

Superfluidity is a bizarre consequence of quantum mechanics. Cool helium atoms close to absolute zero and they start behaving as a single quantum object rather than a group of individual atoms. At this temperature, the friction that normally exists between atoms, and between atoms and other objects, vanishes, creating what is known as a superfluid.

To see if molecules could be made superfluid, Robert McKellar of the National Research Council of Canada in Ottawa and colleagues turned to hydrogen, which exists as pairs of atoms. The team created a compressed mixture of hydrogen and carbon dioxide gas and shot it through a nozzle at supersonic speeds. Once released, the molecules spread apart, cooling and arranging themselves so that each CO2 molecule sat at the centre of a cluster of up to 20 hydrogens.

To test for superfluidity, the team shone an infrared laser at the clusters at wavelengths that CO2, but not hydrogen, can absorb. This set only the CO2 molecules vibrating. Under normal conditions this movement would be slowed down due to friction between the moving CO2 molecules and the surrounding hydrogen. But the researchers found that for clusters of 12 hydrogen molecules, the hydrogen barely impeded the motion of the CO2.

They conclude that these hydrogen clusters are 85 per cent superfluid (Physical Review Letters, DOI: 10.1103/PhysRevLett.105.133401).

via First frictionless superfluid created - physics-math - 07 October 2010 - New Scientist.

Superfluids are very interesting. Helium-4 becomes a superfluid when lowered to 2.17 degrees Kelvin.
A superfluid is a state of matter where the fluid has zero viscosity. This means that the fluid can overcome friction. This is not all, it also has zero entropy and infinite thermalconductivity. By having zero entropy, the substance’s molecules are in perfect order and lose no energy is lost in doing work, the energy transferred when a force is exerted. Infinite thermalconductivity indicates that the substance that conducts all thermal energy injected into it in real time.

via saschina.org

Could there be a room temperature superfluid?
Because graphene is an atomically two-dimensional gapless semiconductor with nearly identical conduction and valence bands, graphene-based bilayers are attractive candidates for high-temperature electron-hole pair condensation.

via aps.org

What could you do with a room temperature superfluid?
May 7, 2008 - "If confirmed in experiments, the material might be used to make low dissipation electronic devices in the future and even help extend Moore's law for another decade."

via Nanotechweb

Moore's law describes a long-term trend in the history of computing hardware. The number of transistors that can be placed inexpensively on an integrated circuit has doubled approximately every two years. The trend has continued for more than half a century and is not expected to stop until 2015 or later. - wikipedia

Moore's law is about the number of transistors, but another limit computing power limit: the noise barrier.

In 2001, Pat Gelsinger, then the chief technology officer of Intel, made a striking prediction about the future of microchips. If current design trends continue, he said, microchips will be running at 30 gigahertz by the end of the decade. However, he added, at this speed they will be generating more heat per cubic centimetre than a nuclear reactor.


Sure enough, by 2003, Intel and other chip-makers had found that their plans for faster processors were running into trouble. For a chip to speed up, its transistors need to be shrunk, but smaller transistors must consume less power or they overheat. With chip-makers unable to keep to the reduced heat budget, the race for faster chips hit a wall....


At best, today's microprocessors can operate at just 3 GHz or so. To deliver a major performance boost, chip-makers have resorted to putting several processors, or cores, on the same chip. This keeps heat at manageable levels. Just.


Designing transistors that need far less power is, it turns out, no easy task. One of the main reasons is that microchips still require plenty of power to overcome electrical noise, which tends to flip the 1s and 0s in digital data, destroying information. ...


The effects of noise become more serious in chips that run at low power since the actual signals being handled by a chip become smaller and can be more easily overwhelmed. ...


via NewScientist



One solution engineers are working on is called phonon computing. The idea is to find ways to use and tame the noise.


Noise is the result of stray energy, which is detectable also as heat.




Every time the transistors in a gate change state, they leak a little electricity. This electricity creates heat. As transistor sizes shrink, the amount of wasted current (and therefore heat) has declined, but there is still heat being created. The faster a chip goes, the more heat it generates. Heat build-up puts another limit on speed.


via Howstuffworks



If a room-temperature superfluid could be harnessed to create transistors which do not leak electricity, then you would not have a noise problem...




Researchers are running into the physical limits of speed and scaling in silicon transistor technology, forcing them to look elsewhere for next-generation devices. The leading candidate to replace silicon being pursued by, well, pretty much everyone, is graphene. Graphene, single sheets of graphitic carbon, is exciting because it is a single atom thick and has remarkably high electron mobilities (100 times greater than silicon), making it ideally suited to atomic-scale, high-speed operation. Also, graphene's electrical properties can be controlled, switching it among conducting, semiconducting and electrically insulating forms. That means graphene-only (or, more likely, graphene-mostly) devices are, in principle, possible. ... In this week's Science, researchers from IBM demonstrate graphene-based field effect transistors (FETs) that may operate at much higher speeds (100GHz) than Si FETs. - Feb 4, 2010


- via arstechnica



 

 

1 comment:

Ryan Elson said...

this is free energy. Room temperatures would make this extremely nice. If this were like helium II at ultra-cold temperatures it could flow up a container. If it were ferrous or could be coaxed into behaving like a ferrous material, then a small magnetic field could cause flow up a container into a bulb, a cylinder with two such bulbs on it could work like a teeter totter and this mechanical motion could be harvested on a larger scale device to generate free electricity simply by applying a magnetic field less powerful than net energy generation to merely encourage the pooling of the superfluid into these bulbs. Mechanically move this magnet back and fourth to produce gradually building motion that offsets the magnet back and fourth, and voila free energy. Or at least perpetual motion.