Archive for January, 2009

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Reinventing the dismal science

Tuesday, January 20th, 2009

dismal-science

The discipline of economics in crisis. The credit crunch has exposed many economists’ most cherished ideas for the nonsense they manifestly are. With its theories in tatters, what now for the dismal science?

It looks as if the best bet is take a a few leaves out of some network science text books. Economies are complex networks, after all, although economists have failed to notice.

Until now! One of the first onto the network bandwagon is Nobel prize-winner Jo Stiglitz from Columbia University and a few pals who have been examining the Japanese credit network between banks and quoted firms in 2004.

Since the collapse of the bubble economy in the early 90s, the Japanese banking system has been going through a similar crisis to the one sweeping the west, so there is plenty to learn (not least of which is the time it can take to turn things around, although most western economists are ignoring this at present) .

The paper makes both heartening and frightening reading. (more…)

Posted in At the seaside, Fightin', Pennies and cents | 3 Comments »

Spotting alien Earths on the cheap

Monday, January 19th, 2009

alien-earth-spotting

Spotting Earth-like planets orbiting other stars is all the rage these days. But unless you have access to a space-based telescope it’s kinda tricky.

The problem is that the reflected light from a Jupiter-sized planet is roughly 10^4 fainter than the parent star. That’s hard to spot at any time but when this is coupled with the distortion that the Earth’s  atmosphere introduces, these planets become almost impossible to see.

One way around this is to use adaptive optics to smooth out distortions in the wavefront from the star system as it hits the telescope’s mirror. But these systems are expensive and the demands of higher resolution make them increasingly complex too.

Another option is to take exposures that are much shorter than the time over which the atmospheric distortion occurs. Then post processing of the image compared to the image of a reference star allows the distortion to be removed.

The trouble with this technique is that the wavefront distortion varies over the entire area of the telescope’s mirror. So this kind of processing ends up averaging the distortion rather than removing it.

Takayuki Kotani from the  Observatoire de Paris in France et amis are pioneering a technique called pupil remapping that could get around this.  Their idea is to place a bundle of optical fibres at the focal point of the telescope. These channel the light from each point in the mirror separately, which avoids the problem of averaging out the distortion and allows much better image processing.

They’ve tested the idea on an optical bench showing that it can achieve near theoretical performance. Installed in a decent telescope, it should allow a dynamic range of around 10^6. That will allow the detection of much fainter planets than is now possible and at a fraction of the cost of high resolution adaptive optics  or space-based telescopes.

Expect to see this technique producing good results in ground-based telescopes within months.

Ref:  arxiv.org/abs/0901.2165: Pupil Remapping for High Contrast Astronomy: Results From an Optical Testbed

Posted in Stars in their eyes | Comments Off on Spotting alien Earths on the cheap

Tango ‘n’ foxtrot

Saturday, January 17th, 2009

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

The Chemical Diversity of Comets

A Mathematical Proof of The Existence of Trends in Financial Time Series

The WMAP Cold Spot

Why Do Dolphins Form Mixed-Species Associations in the Azores?

New Kinds of Quantum Statistics

Posted in Cherry pickin' | Comments Off on Tango ‘n’ foxtrot

The waltz of the spherical algae

Friday, January 16th, 2009

volvox-fluid-flow

“Long after he made his great contributions to microscopy and started a revolution in biology, Antony van Leeuwenhoek peered into a drop of pond water and discovered one of nature’s geometrical marvels,” say Ray Goldstein and pals at the University of Cambridge in the UK.

Val Leeuwenhoek had discovered Volvox, a spherical green algae that uses thousands of cells with flagellla to move around.

Because of its size, Volvox is relatively easy to study and Goldstein and co have been keeping a close eye on the organism, watching the way it moves and the flow of fluid around it as it does so.

They’ve also found some unusual behaviours. In certain circumstances, Volvox likes to team up with a partner and waltz through the water like they’d been watching Strictly Ballroom.

The team say that the forces responsible for bringing the partners together are “short-range lubrication forces”, whatever they are, and that the creatures have probably evolved to take advantage of the opportunity this affords for some hanky panky. That must be first in hydrodynamics research.

The team have put together a set of fascinating videos showing Volvox in action which is recommended viewing for all algae.

Ref:

Dancing Volvox : Hydrodynamic Bound States of Swimming Algae

Posted in Slimey stuff | Comments Off on The waltz of the spherical algae

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…

(more…)

Posted in Changin' the world, Cold 'n' cool, Mean machines, Seein' the light | 1 Comment »

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).

(more…)

Posted in Changin' the world, Hellraisin', Pennies and cents | 2 Comments »

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.

(more…)

Posted in Changin' the world, Slimey stuff | Comments Off on How to spot vegetation on Earth-like planets

Harvesting energy from the airwaves

Monday, January 12th, 2009

nanohelices

Antennae are the most fundamental energy harvesting devices that we know, says Sung Nae Cho at the Samsung Advanced Institute of Technology in south Korea. So why aren’t they more widely used?

Turns out that helical antennae are already used to harvest energy and most of us probably own one already in the form of a transformers. These contain a helical winding that rectifies  AC into DC.

Cho points out that it has recently become possible to build nanohelices and that these might also be used for rectification. He’s designed a device that rectifies, not current, but electromagnetic waves. It consists of a nanohelix layer, a diode  layer and a capacitor layer, all the components of a standard rectifying circuit.

The nanohelix layer consists of an array of  100 million “pixels” which each contain a single nanohelix. That makes the array no bigger than the imaging chips in digital cameras . Cho calculates that if only 10 per cent of the nanohelices harvest energy from ambient electromagnetic waves to the tune of 130 nA, then the device would produce 1.3A.

If he’s right, that’s a handy amount by any standards. Anybody volunteer to prove him right.

Ref: arxiv.org/abs/0901.0769: Energy Harvesting by Utilization of Nanohelices

Posted in Calculatin', Mean machines, Sparks 'n' thunderbolts | 3 Comments »

Ohms ‘n’ bytes

Saturday, January 10th, 2009

The best of the rest fromthe physics arXiv this week:

Folding@Home and Genome@Home: Using Distributed Computing to Tackle Previously Intractable Problems in Computational Biology

Dark Matter — a Review

Sociology of Modern Cosmology

Writing Electronic Devices on Paper with Carbon Nanotube Ink

Cloud Computing and Grid Computing 360-Degree Compared

Posted in Cherry pickin' | Comments Off on Ohms ‘n’ bytes

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.

(more…)

Posted in Changin' the world, Secrets | 14 Comments »

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