Archive for the ‘Changin' the world’ Category

Centimetre scale models could compute Casimir forces

Thursday, March 5th, 2009

casimir-computer

The Casimir force is notoriously difficult to measure. So tricky is it, that the first accurate measurements weren’t made until 1997 and even today only a handful of labs around the world of capable of taking its measure.

Of course there are various ways of modelling what goes on theoretically but even the most powerful simulations these struggle to cope with simple shapes let alone complex geometries. Consequently, our knowledge of the Casimir  force and how to exploit it is poor.

Now John Joannopoulos and pals at MIT are suggesting a rather entertaining third way: to calculate Casimir forces using scale models that work like analogue computers.

What the team has noticed is a mathematical analogy between the Casimir force acting on microscopic bodies in a vacuum and the electromagnetic behaviour of macroscopic bodies floating in a conducting fluid.

So imagine you want to know what Casimir forces will act on a particular geometry. The idea is to build a centimetre scale metal model of this set up and place it in a conducting liquid such as saline. Then bombard it with microwaves and see what happens.

The result should give an accurate representation of the Casimir forces that would act on the microscopic scale.

The group explains:

Such a centimeter-scale model is not a Casimir “simulator,” in that one is not measuring forces, but rather a quantity that is mathematical related to the micron-scale Casimir force. In this sense, it is a kind of analog computer.

There’s no reason why those kinds of tests can’t be done now.  And that should give researchers a way of testing machines designed to reliably exploit the Casimir force for the first time.

Ref: arxiv.org/abs/0903.0599: Ingredients of a Casimir Analog Computer

Liquid film motors finally explained

Thursday, February 26th, 2009

liquid-film-motor-explained

Last year, a group of Iranian physicists made the extraordinary discovery that motors can be made of nothing more than a thin film of water sitting in a cell bathed in two perpendicular electric fields. The unexpected result of this set up is that the water begins to rotate. Divide the water into smaller cells and each rotates too.

The team at the Sharif University of Technology in Tehran have a number of  fascinating videos of it in action. They raise an interesting question: the electric fields are static, so what’s making the water move?

Now Vlad Vladimirov at York University in the UK and a couple of droogs from Russia have delved into the hydrodynamics to work out what’s putting the oomph in this motor. The key turns out to be the scale on which the effect takes place.

They say the flow is generated at the edge of the cell where the electric field crosses the  (dielectric) boundary between the water and the cell container. The change in field sets the water flowing along the boundary.  Crucially, this flow is opposite on the other side of the cell and this is what sets up the circular flow.

Vladimirov and co point out that this effect can only happen in a thin film where effects such as viscosity and friction play a large role in the dynamics. In larger bodies of water, these effects become insignificant and the rotation stops. Which is why these motors have only ever been seen in thin films.

That has important implications becaue it shows the scale dependency of important phenomena. In fact, liquid film motors may turn out to be a game-changers for anybody involved in microfluidics.

Ref: arxiv.org/abs/0902.3733: Rotating Electrohydrodynamic Flow in a Suspended Liquid Film

Human eye could detect spooky action at a distance

Thursday, February 19th, 2009

mantanglement

It’s almost a year since Nicolas Gisin and colleagues at the University of Geneva announced that they had calculated that a human eye ought to be able to detect entangled photons. “Entanglement in principle could be seen,” they concluded.

That’s extraordinary because it would mean that the humans involved in such an experiment would become entangled themselves, if only for an instant.

Gisin is a world leader in quantum entanglement and his claims are by no means easy to dismiss.

Now he’s going a step further saying that the human eye could be used in a Bell type experiment to sense spooky-action-at-a-distance. “Quantum experiments with human
eyes as detectors appear possible, based on a realistic model of the eye as a photon detector,” they say.

One problem is that human eyes cannot se single photons–a handful are needed to trigger a nerve impulse to the brain.

That might have scuppered the possibility of  a Bell-type experiment were it not for some interesting work from Francesco De Martini and buddies at the Universityof Rome, pointing out how the quantum properties of a single particle can be transferred to an ensemble of particles.

That allows a single entangled photon, which a human eye cannot see, to be amplified into a number of entangled photons that can be seen. The eye can then be treated like any other detector.

This all looks like fun. The first person to experience entanglement –mantanglement–would surely be destined for some interesting press covereage.

But the work raises an obvious question: why is Gisin pursuing this line? The human eyeball could be put to use in plenty of optics experiments, so why the focus on mantanglement?

Could it be that Gisin thinks there is more to entanglement than meets the eye?

Ref: arxiv.org/abs/0902.2896: Quantum experiments with human eyes as detectors based on cloning via stimulated
emission

Trick of the light boosts atom interferometer sensitivity

Thursday, January 15th, 2009

atom-interferometer

While preparing for the job of US Secretary of Energy in the incoming Obama administration (and being  director of one the top labs in the US and Nobel Prize winner to boot), Steven Chu has somehow found time to post the results of his latest experiment on the arXiv. And it’s an impressive piece of work too.

Chu, who is director of the Lawrence Berkeley National Laboratory, and his colleagues have built an atom interferometer with a sensitivity that is dramatically higher than previous models. To prove its worth, they’ve measured the fine structure constant to an accuracy of 3.4 parts per billion, which is within an order of magnitude of the best measurements.

But the real benefit of the new device is that, among other things, it will allow a new generation of tests of the equivalence principle. That is, it will test whether  the m in F=ma and the m’s in F = Gm1.m2/r^2 refer to the same thing.

In physics-speak, the question is whether gravitational and inertial mass are the same. It’s something we always assume but have never proven and there are a number of ongoing programs to study the question.

Here’s how Chu’s work will change the game…

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How the credit crisis spread

Wednesday, January 14th, 2009

credit-crisis-spread

Where did the credit crunch start? According to Reginald Smith at the Bouchet-Franklin Research Institute in Rochester, it began in the property markets of California and Florida in early 2007 and is still going strong.

To help understand how the crisis has evolved, Smith has mapped the way it has spread as reflected in the stock prices of the S&P 500  and NASDAQ-100 companies. The picture above shows how the state of affairs changed between August 2007 and October 2008. Each dot represents a stock price and the colour, its return (green equals bad and red equals catastrophic).

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How to spot vegetation on Earth-like planets

Tuesday, January 13th, 2009

earthlike-planet

In December 1990, scientists analysing data from the Galileo spacecraft found compelling evidence for the existence of life in space.

The data famously came from the craft’s first fly by of Earth, a planet on which life seemed a definite possibility.  The exercise led to the establishment of a number of criteria that if found elsewhere, would point to the existence of life

Among the most persuasive of these criteria is the vegetation red edge–a sharp increase in the reflectance of light at a wavelength of around 700 nm.  This is the result of chlorophyll absorbing visible light but reflecting near infrared strongly which Galileo found strong evidence for.

Assuming alien plant life is similar to ours,  could we spot a vegetative red edge on an Earth-like planet orbiting a star several light years away, asks Luc Arnold at the Saint-Michel-l’Observatoire in France and amis.

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Memristors made into low cost, high density RRAM (Resistive Random Access Memory)

Friday, January 9th, 2009

memristor-memory

The four passive components of electronics are the resistor, capacitor, inductor and the memristor, which was discovered only a few months ago.

Memristors (from memory-resistors, geddit?) are resistors whose resistance depends on their past.  In that sense they remember the past or, as an electronics engineer might put it,  they store information.

So new are memristors that nobody has had much time to think about what they might be useful for. That’s changing quickly.

A couple of months back we saw how they could be used to make neural nets that mimic the “intelligent” behaviour  of slime mould.

Now Tom Driscoll and buddies at the University of California, San Diego have shown how memristors could work as low cost, high density memory.

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How bacterial colonies could drive rotors

Tuesday, December 16th, 2008

bacterial-rotor

E coli bacteria use motors called flagella to generate a force that pushes them along at a rate of up to 10 body lengths per second. That’s a fair rate of knots and in recent years several groups have used this force to turn microrotors. Their approach is to bond the bacteria to a rotor like carthorses to a millstone. That certainly works, but it’s time consuming and fiddly, especially when the workforce dies on you.

But there is a cleverer way, say Luca Angelani and pals from the University of Rome in Italy. Simply place an asymmetric cog in a bath of moving bacteria and they will start it spinning for you.

That sounds a bit like extracting kinetic energy from the random motion of particles, which we know to be impossible because the motion is symmetric in time.

But Angelani and co say there is in important difference between this and bacterial motion: the former is in equilibrium but the latter is an open system with a net income of energy provided by nutrients. This breaks the time symmetry allowing energy to be extracted in the form of directed motion.

Angelani and co calculate that their bacterial bath could turn an asymmetric gear at a rate of a few rpm, which is an interesting result.

Our findings can open the way to new and fascinating applications in the field of hybrid bio-microdevices engineering, and also provide new insight in the more fundamental aspects of nonequilibrium dynamics of active matter.

That sounds exciting and the effect doesn’t look hard to confirm experimentally. Which begs the question: what are they waiting for?

Ref: arxiv.org/abs/0812.2375: Self-Starting Micromotors in a Bacterial Bath

Graphene transistors clocked at 26GHz

Thursday, December 11th, 2008

graphene-transistor

IBM has seen the future of computing and it may not involve silicon. Instead the company has been looking at graphene, the single atom-thick sheets of carbon that has materials scientists entranced by its dazzling array of amazing properties.

If graphene ever becomes the material of choice for a new generation of superfast chips, then the work of Yu-Ming Lin and buddies at the IBM T. J. Watson Research Center in upstate New York may well turn out to be one of the foundations of that revolution.

Today, they say they’ve built the high quality graphene transistors and clocked them running at 26 GHz.

That doesn’t quite knock silicon off its perch–the fastest silicon transistors are an order of magnitude faster than that but the record is held by indium phosphide transistors which have topped 1000 GHz.

Still, 26 GHz isn’t bad for the new kid on the block. It took silicon 40 years to get this far. By contrast, the first graphene transistor was built only last year.

As the team puts it: “The work represents a significant step towards the realization of graphene-based electronics.”

Ref: arxiv.org/abs/0812.1586: Operation of Graphene Transistors at GHz Frequencies

The cosmic ray revolution

Wednesday, November 12th, 2008

Cosmic rays, the high energy protons and helium nuclei that constantly bombard the Earth, have puzzled astronomers for the best part of one hundred years. Where do they come from and how are they accelerated to energies in excess of 10^20 eV—that’s about the energy that Roger Federer gives a tennis ball during a serve? (By contrast, the  Large Hadron Collider will be able to accelerate protons to a mere  10^12 eV.)

To tackle these questions, astronomers have built a giant cosmic ray telescope about the size of Rhode Island in Argentina. It’s called the Pierre Auger telescope and in the short time it has been operating, it is already challenging astronomers’ views about the origin of cosmic rays. In particular, it’s beginning to look as if the highest energy comsic rays come from active galactic nuclei.

Serguei Vorobiov from University of Nova Gorica in Slovenia summarises the highlights. Worth a read if you want to get up to speed on a new generation of astronomy.

Ref: arxiv.org/abs/0811.0752: The Pierre Auger Observatory — a New Stage in the Study of the Ultra-High Energy Cosmic Rays