Archive for December, 2008

The strange right hand of the universe

Monday, December 22nd, 2008

galactic-handedness

Is the Universe right handed? If Michael Longo at the University of Michigan in Ann Arbor is to be believed, the answer is yes; and the evidence comes from the right or left-handed shape of spiral galaxies.

Astronomers have images of many thousands of spiral galaxies. But classifying them as left or right handed is tricky for a computer program. So a project called the Galaxy Zoo asks humans to analyse galaxies and mark them as either left or right handed.

It’s fair to say the results have caused some controversy. The Universe, according to this data, seems to prefer right-handed galaxies and by some distance.

Various critics have said this is a result of the way the tests are set up and that we humans have an in-built bias for right-handed spirals. But this has been challenged by other data. Longo has trawled through the lot and and has settled on the conclusion that there is some kind of universal preference for right handedness, an Axis of Evil along which galaxies tend to spin.

What to make of this claim? Longo says that various studies have shown all kinds of biases, some such as the cold spot in the cosmic background radiation, more convincing than others.

But it always pays to tread carefully in areas like this. A number of claimed biases have disappeared after a more thorough analysis of the data.

A fascinating idea it may be, but we need to treat claims of a universal handedness with caution.

Ref: http://arxiv.org/abs/0812.3437: Does the Universe Have a Handedness?

Hot ‘n’ quick

Saturday, December 20th, 2008

The best of the rest from the physics arXiv this week:

Probing the Membrane Potential of Living Cells by Dielectric Spectroscopy

Selective Optical Charge Generation, Storage and Readout in a Single Self Assembled Quantum Dot

Quantum Vacuum Experiments Using High Intensity Lasers

The Hydrodynamics of Swimming Microorganisms

Similar is Better: Speed Variability Reduces Traffic Flow

Astronomers find hottest and fastest exoplanet

Friday, December 19th, 2008

wasp-12b-data

As astronomers discover greater numbers of planets orbiting other stars, they are able to revise their theorie sof planet formation accordingly. Exotic planets are particularly prized because they push the boundaries of theoretical understanding to its limits.

Today,  Leslie Hebb  at the University of St Andrews in Scotland and colleagues announce the discovery of one of the most exotic planets yet seen. WASP-12b orbits a star about 3 times as bright as the sun. Its orbit has a radius about 1.8 times that of Jupiter  but it is only about a quarter as dense.

But get this. WASP-12b has an orbital period of only  1.09 days, the shortest ever seen, and a surface temperature of 2516 K because it is the most highly radiated planet ever discovered. That’s too records for one planet.

How these kinds of planets can form, nobody is certain. But one thing’s for sure: WASP-12b must be on one helluva roller coaster ride.

Ref: arxiv.org/abs/0812.3240: WASP-12b: the Hottest Transiting Extra-Solar Planet Yet Discovered

Why astronomical units need to be redefined

Thursday, December 18th, 2008

In 1983, the International Bureau of Weights and Measures defined the metre as the distance travelled by light in a vacuum in 1⁄299,792,458 of a second. That makes a metre a fixed unit of length.

For astronomers, however, distance is rather more malleable. In astronomy, distance is measured in astronomical units. Astronomers think of an au as the distance between the Earth and the Sun.
But since the Earth’s orbit is elliptical, this distance isn’t constant. At one time an au was defined as the length of the semi-major axis of the Earth’s orbit. But that isn’t constant either.

So in 1976, the Bureau International des Poids et Mesures in France defined the au to be the distance from the centre of the Sun at which a particle of negligible mass would orbit in 365.2568983 days.

The trouble with this definition is that it depends both on the mass of the Sun and the gravitational constant G.

That’s not good say, Nicole Capitaine and Bernard Guinot at the Observatoire de Paris. The gravitational constant and the mass of the sun can only be measured with limited accuracy. And who’s to say their value isn’t changing anyway? It makes no sense to define a fundamental unit of length in these terms.

They say astronomers desperately need a new definition and point out there is an obvious choice: define an au as some suitable multiple of a metre.

That would bring astronomy into line with SI units and making various calculations much more straightforward.

So what are they waiting for?

Ref: arxiv.org/abs/0812.2970: The Astronomical Units

2D image created from a single pixel sensor

Wednesday, December 17th, 2008

ghost-imaging

Ghost imaging is a curious phenomenon that has had numerous physicists scratching their heads in recent years.

It works like this: take two beams of entangled photons and aim the first at an object. The transmitted photons from the object are then collected by a single pixel detector.

The second beam is aimed at a CCD array without ever having hit the object.

It turns out it is possible to reconstruct an image of the object–a so-called ghost image–by matching the data from the two detectors, even though the single pixel detector has no spatial resolution.

When this was first demonstrated in 1995, everybody was amazed by the strange power of quantum entanglement.

But later, various groups showed that entangled beams weren’t necessary at all and that ordinary light from a pseudothermal source would do the job just as well.

While interesting, that doesn’t actually rule out the possibility that the two beams may be correlated in some entangled-like quantum way, however.

So the question of whether quantum entanglement is responsible or not has remained open. Until now.

Yaron Silberberg and pals from the Weizmann Institute of Science in Israel, have carried out an ingenious experiment that settles the matter.

They use only one beam, which they use to illuminate the object, and collect the transmitted photons using a single pixel detector. They then calculate theoretically what the second beam should look like and combine the single pixel data with this “virtual beam”.

And get this: they still see a ghost image. That’s a 2D image from a single pixel detector! And a pretty convincing demonstration that quantum entanglement cannot be responsible.

The question now is: what kind of classical information processing allows the reconstruction of a 2d image from a single pixel sensor? That’s a real puzzle.

Ref: arxiv.org/abs/0812.2633: Ghost Imaging with a Single Detector

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

Solving stiction in MEMs devices

Monday, December 15th, 2008

acoustic-casimir-force

Microelectromechanical devices were supposed to change the world, so where are they?

A few designs have leaked out, such as the accelerometers in air bags. But most have remained stubbornly, and literally, stuck in the lab.

One of the troubling secrets about MEMs is that many designs simply don’t work because their moving parts become stuck fast and refuse to budge.

Engineers call this “stiction”: a vaguely defined force that affects small parts but not large ones (where inertia plays a greater role in overcoming these forces). Stiction is thought to be caused variously by Van der Waals forces, electrostatic forces, hydrogen bondng and even the Casimir force, perhaps in combination. That’s why it’s so hard to avoid.

Now Raul Esquivel-Sirvent and a buddy at the Universidad Nacional Autonoma de Mexico in Mexico City, have a potential solution based on the acoustic Casimir force, an acoustic analogue of the more famous quantum Casimir force which was discovered 10 years ago by Andres Larraza, then at the Naval Postrgraduate School in Monterey.

Here’s the idea: place a couple of parallel plates close together and blast them with sound waves of a specific frequency range. If the waves are larger than the gap between the plates, they will tend to push them together but if they are smaller, they will squeeze into the gap and tend to push them apart. So changing the wavelength or the distance between the plates switches the direction of the force.

That could be useful for microswitches in MEMs devices, says Esquivel-Sirvent. But more interestingly, it could also be used to separate microcomponents that have become stuck together. Perhaps the promise of MEMs will be realised at last.

Ref: arxiv.org/abs/0812.2213: Pull-in Control in Microswitches Using Acoustic Casimir Forces

Hertz ‘n’ pain

Saturday, December 13th, 2008

The best of the rest from the physics arXiv this week:

Molecular Signatures in the Near Infrared Dayside Spectrum of HD 189733b

A New Metric for Robustness with Respect to Virus Spread

Combining Chromosomal Arm Status and Significantly Aberrant Genomic Locations Reveals New Cancer Subtypes

Ultracold Molecules: Vehicles to Scalable Quantum Information Processing

Ten New and Updated Multi-planet Systems, and a Survey of Exoplanetary Systems

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

How to decelerate a molecule

Wednesday, December 10th, 2008

molecule-decelerator

When it comes to shuttling individual atoms about, physicists have made giant strides in cooling, trapping and even collimating them into matter wave beams. These kinds of tricks are already being used for matter-wave interferometry on chips.

But if you want to do the same kinds of things with molecules, you’re out of luck. There are two problems. First, molecules are much harder to slow down and trap in decent quantities. And second, they are much more difficult to ID. Atoms are usually identified by the light emitted by electronic transitions, which are usually in the visible part of the spectrum. In most molecules, however, these transition are in the UV and so much harder to access.

Now Samuel Meek and friends from the Fritz-Haber Institute, a Max Plank Institute in Berlin, have tackled one of these problems by building a molecular decelerator on a chip. The device consists of an array of electrodes that create an electric field with a local minimum, or well, that polar molecules tend to fall into. The well can be moved along the array.

Decelerating molecules is then a matter of matching the velocity of the well to that of the incoming molecules and then rapidly slowing it down. Meek and co say that in this way they have halved the kinetic energy of carbon monoxide molecules by slowing them from 360m/s to 240m/s.

That’s impressive and the team reckons that with a little tweaking, the chip will be able to bring the CO molecules to a standstill.

Strangely, nobody has given much thought to what you can do with stationary CO molecules. One option is to use them to store qubits for quantum computing but there seem to be few other ideas.

Which means there’s a good opportunity here for a creative thinker to make a mark.

Ref: arxiv.org/abs/0812.1487: A Stark Decelerator on a Chip