Archive for January, 2008

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The bar at the heart of the galaxy

Friday, January 11th, 2008

Barred galaxy formation

Bars are common features of galactic structure but we ain’t talking whiskey chasers. 56 per cent of galaxies have strong bars and a large fraction of these have spiral arms emanating from the ends of the bars. The question: is how did these structures form and why are they so common?

Now Merce Romero-Gomez at the Laboratoire d’Astrophysique de Marseille in France and some buddies have worked it out saying that bars form naturally because of instabilities that occur in the orbits of large structures like galaxies.

The pictures say it all.

Ref: arxiv.org/abs/0712.4391: The Formation of Spiral Arms and Rings in Barred Galaxies

Posted in Stars in their eyes | Comments Off on The bar at the heart of the galaxy

Information and evolution

Thursday, January 10th, 2008

Cells and information

Living things need to know what conditions are like in the outside world so they can adapt to their environment. Is there food, light, heat out there and if so, where. So a certain amount of information must flow into the organism.

This information flow is crucial–without it life could not exist so it’s reasonable to assume that evolution must have selected organisms on the basis of their ability to handle this flow. But how could you prove this?

Samuel Taylar at Princteon University and a few pals have examined this idea in detail and discovered that in single celled organisms “the minimum information required for reasonable growth rates is close to the maximum information that can be conveyed through biologically realistic regulatory mechanisms“.

Case closed.

Ref: arxiv.org/abs/0712.4382: Information and Fitness

Posted in Slimey stuff | Comments Off on Information and evolution

The Turing alternatives

Wednesday, January 9th, 2008

Alternative Turing tests

Ya’ll heard of the Turing test for measuring machine intelligence. Seems kinda odd, doncha think, that after 50 years we ain’t never thought of any other ways to test machine intelligence.

Same thing occurred Shane “Hind” Legg at the IDSIA (Istituto Dalle Molle di Studi sull’Intelligenza Artificiale) in Switzerland and his buddy Marcus so they delved into the topic. Turns out, various researchers have come up with interesting machine intelligence tests which have been ignored by the community. So Shane and Marcus and have listed them all for ya on the arXiv.

Here are some highlights:

Compression: a machine intelligence has to compress a corpus of knowledge. This can only be done effectively when the machine has some understanding of the knowledge which allows it to extract some kind of overall structure. So a measure of compression can be interpreted as a measure of understanding

Linguistic complexity: measuring a machine’s conversational ability using techniques developed for tracking the complexity of children’s language

Competitive games: a broad definition of intelligence is the ability to do well at a wide range of tasks. So one idea is to test machines against each other on a wide range of games

The paper contains other tests so feel free to take a look.

Ref: arxiv.org/abs/0712.3825: Tests of Machine Intelligence

Posted in Calculatin', Mean machines | 4 Comments »

The puzzle of flyby anomolies

Tuesday, January 8th, 2008

Flyby inertia

On 8 December 1990, something strange happened to the Galileo spacecraft as it flew past Earth on its way to Jupiter. As the mission team watched, the spacecraft’s speed suddenly jumped by 4 mm per second. Nobody took much notice — a few mm/s is neither here or there to mission planners.

Then on 23 January 1998, the same thing happened to NASA’s Near spacecraft as it swung past Earth. This time its speed jumped by 13 mm/s.

The following year, Cassini’s speed was boosted by 0.11mm/s during its Earth fly-by.

And people finally began to ask questions when the Rosetta spacecraft’s speed also jumped by 2 mm/s during its 2005 close approach.

Nobody knows what causes these jumps but Magic McCulloch, an unaffiliated astrothinker from the UK has an interesting proposal. He suggests that a sudden change in inertia might occur when objects experience very low accelerations.

The thinking goes like this: inertia is the result of pressure from so-called Unruh radiation which objects experience only when they accelerate. At very low accelerations, the wavelength of this radiation is so large that it does not fit within the universe (ie it is greater than the Hubble distance). As the acceleration increases, the wavelength drops to less than the Hubble distance and the spacecraft appears to receive a kick. (A similar wavelength related phenomenon happens with the Casimir force.)

McCulloch says his idea could be tested in low acceleration experiments using an invisibility cloak designed to make an object invisible to Unruh radiation (although it’s a big jump from making these cloaks for microwave radiation and visible light to making them for Unruh raditation). So it wouldn’t experiecne inertia in the same way.

Interesting idea.

Ref: arxiv.org/abs/0712.3022: Can the Flyby Anomalies be Explained by a Modification of Inertia?

Posted in Mean machines, Weird 'n' spooky | 2 Comments »

How to spot a wormhole

Monday, January 7th, 2008

Wormhole

I know ya’ll heard of wormholes, tunnels in the fabric of the cosmos that connect one region of the universe to another. These ain’t just the fanciful dreams of impressionable young astrobods: wormholes represent real solutions of Einstein’s equation of general relativity. If general relativity is correct, wormholes ought to be out there somewhere.

But how to spot ’em? It’s easy to imagine that a wormhole, being a kinda hole in spacetime, would be indistinguishable from a black hole. Turns out that ain’t the case. Alexander Shatskiy, an astrothinker from the Lebedev Physical Institute in Moscow, says wormholes are fundamentally different from black holes because they have no event horizon. He’s even worked out what a wormhole should look like.

The key difference is that light entering one end of a wormhole comes out at the other but in a highly characteristic way. The angular intensity distribution of this light has a minimum at the center, regardless of wavelength. This allows background stars to shine through giving the wormhole the appearance of a semi-transparent hollow sphere (see image above).

Where to look? Shatskiy suggests that the next generation of supersensitive radio telelscope interferometers should have the resolution capable of distinguishing black holes from wormholes in active galactic nuclei.

So the message to all you radio astronomers out there is: keep ’em peeled.

Ref: arxiv.org/abs/0712.2572: Passage of Photons Through Wormholes and the Influence of Rotation on the Amount of Phantom Matter around Them

Posted in Changin' the world, Seein' the light | 3 Comments »

In case ya missed ’em…

Sunday, January 6th, 2008

…a round up of this week’s posts:

Best of the arXivblog: Breaking the Netflix prize dataset

Best of the arXivblog: Why our time dimension is about to become space-like

How to predict a brainquake

Graphite valley

The cold dark matter scrap

Posted in Highlights | Comments Off on In case ya missed ’em…

Gloves ‘n’ mittens

Saturday, January 5th, 2008

The best of the rest from the physics arXiv:

Quantum Nanomagnets and Nuclear Spins: an Overview

A Model for Erosion-deposition Patterns

Testing Atom and Neutron Neutrality with Atom Interferometry

Modelling the Navigation Potential of a Web Page

The Balloon-borne Large Aperture Submillimeter Telescope: BLAST

Posted in Cherry pickin' | Comments Off on Gloves ‘n’ mittens

The cold dark matter scrap

Friday, January 4th, 2008

WIMP

There’s a race on to find the first direct evidence of cold dark matter. And it ain’t pretty. There’s probably a Nobel at stake for the winner which means the leading groups are at each other’s throats, like alleycats over chicken bones.

For any of ya’ll who wanna know who’s who in this backstreet brawl, Laura Baudis at the University of Zurich has compiled a card of the main fighters. All these guys are lookin’ for Weakly Interacting Massive Particles and she gives a good summary of all the contenders looking to be crowned king of  WIMPs.

The basic idea is that WIMPs sit around in space twiddling their thumbs until a great big lump of ordinary stuff like the Earth comes along and smashes into them. When this happens physicists should be able to see the impact in their labs as atoms get pranged.

Laura takes the rather optimistic view that “the major questions have shifted from ’how
to detect a WIMP’ to ’how can we identify its nature in case of a signal’”.

She neatly avoids the biggest question which is whether WIMPs exist at all.

They’ve been imagineered to explain the observation that many galaxies are spinning so fast that the matter they contain ought to be thrown outwards.  Something has to be holding these galaxies together and so astrobods have hypothesised that particles called WIMPs provide the extra gravitational ooomph to hold galaxies together.

But plenty of theorists think other explanations are just as feasible, modified newtonian gravity, for example. And if they’re right, then the hundreds of millions of dollars being spent in this area might as well have been dumped at the bottom of a dirty great mine shaft. Which, as fate would have it, is where most of the WIMP detectors happen to have ended up anyway.

Ref: arxiv.org/abs/0711.3788: Direct Detection of Cold Dark Matter

Posted in Fightin', Mountain climbin' | Comments Off on The cold dark matter scrap

Graphite valley

Thursday, January 3rd, 2008

Graphite

Them chemists have been bewitched by carbon in recent years. Ya can’t move in chemistry departments without being abused ‘n’ bombarded with nanotubes, buckyballs and all mannner of carbononsense. But in all their hurry to blow their own carbon nanotrumpets, it loooks as if they missed a wonder material staring them in the face.

Now physicists are sayin’ that graphene is the material of their dreams and that it could revolitionize everything from fundamental physics to computing. Graphene (a single layer of graphite) has been doing remarkable things for a few years. Physicists have demonstrated the quantum hall effect in graphene and at room temperature for chrissakes! It can switch from a metal-like conductor  to an insulator in the presence of a magnetic field and it is home to a new breed of amazing phantom stuff called 2D Dirac particles that physicists are drooling to get hold of.

So ya can imagine how it could be put to good use to make a new breed of nanodevice. In fact, many commentators expect graphene to play an important role in the new science of spintronics.

Trouble is that graphene ain’t the easiest material to handle. It’s edges are highly reactive and bond to anything within reach and it tends to curl up like paper in fire.

But now Pablo Esquinazi at the University of Leipzig in Germany and a his buddy Yakov say that anything graphene can do, graphite can do better. What they mean is graphite only a few layers thick but this stuff is much easier to make and handle than single layer graphene.

And their conclusion?

“Based on experimental observations, we anticipate that thin graphite samples and not single layers will be the most promising candidates for graphene-based electronics.”

Looks like the area round Palo Alto is gonna need a name change.

Ref: arxiv.org/abs/0712.4020: Graphene Physics in Graphite

Posted in Mean machines, The ant playground | Comments Off on Graphite valley

How to predict a brainquake

Wednesday, January 2nd, 2008

 Brainquake

Welcome back. Hope ya’ll had a good holiday and that 2008 brings your hearts’ desires.

First up this year, a cracker of a paper showing how epileptic fits might be predicted following the discovery of a profound statistical analogy between earthquakes and “brainquakes”.

Ivan Osirio  at the University of Kansas Medical Centre and  a few pals  have studied brain wave recordings taken during more than 16000 seizures in patients with severe epilepsy and compared it to the data from the Southern Californian Seismic Network.

And get this: the data is almost interchangeable. Geophysicists have spotted all kindsa interesting features in earthquake data over the years and now Osirio says the same features are also present in brainquake data.

For example, the Gutenberg-Richter law expresses how the number of earthquakes varies with size–ie few large ones and many small ones, a relationship that holds over many orders of magnitude. Osiris says the same holds true for brainquakes
The frequency of aftershocks decreases in inverse proportion to the time after a quake, a relationship known as Omori’s law. Now Osiris has found the same holds true of brainquakes.

And he goes on. Earthquakes and brainquakes share the same statistical characterstics when it comes to the time between events and with the expected time until the next event depending on the time elapsed since the last one. It’s uncanny.

(Except it ain’t really a surprise since the notion of universality tells us that in certain circumstances radically different systems can have the same scale free behavior.)

But the real surprise is that hidden within the brainquake statistics is a way of spotting them in advance (and therefore of preventing them). Osiris has found that many brainquakes are preceded by foreshocks that go unnoticed by the patient and that these can be reliable indicatoes that a major quake is imminent.

That’s an impressive result. As the authors point out: “a general strategy for forecasting seizures [is] one of neurosciences’ grails”

Ref: arxiv.org/abs/0712.3929: Epileptic Seizures: Quakes of the Brain?

Posted in Changin' the world, Slimey stuff | Comments Off on How to predict a brainquake

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