Archive for August, 2007

Friday’s finds

Friday, August 31st, 2007

Today’s highlights from the preprint server

Coherent ultrafast core-hole correlation spectroscopy: x-ray analogues of multidimensional NMR

Secure Transmission with Multiple Antennas: The MISOME Wiretap Channel

Relationship between degree of efficiency and prediction in stock price changes

Tracing the early development of harmful algal blooms with the aid of Lagrangian coherent structures

Unparticles and supernovas

Friday, August 31st, 2007

Unparticles are all the rage in physics at the moment. Yep, ya heard right: unparticles.

A few months back, Howard “Jumpin” Georgi at Harvard University stumbled across an entirely new type of stuff while foolin’ around with the field theories behind particle physics.

Ordinary particles pop out of these theories as solutions at certain scales. This gives particles a fixed measureable mass.

What Jumpin’ Georgi has found is an entirely new class of solutions that are scale free. That means this stuff has no average size but looks the same whatever scale you choose to examine it at.

This can’t be ordinary particle stuff cos mass is scale dependent–the further away you are from a particle, the smaller it looks, right? (Unless the particles have zero mass, in which case it don’t matter how far away you are, they always look the same. But Georgi ain’t interested in zero mass particles.)

He’s called this stuff unparticles cos it ain’t nothing like the particles we all know and lurv. Georgi’s work has created big excitement. A lot of people are a-scramblin and a-workin to better understand this stuff. You can almost hear that brainpower motorin through the gears.

How might we observe unparticles? Georgi reckons unparticles might interact weakly with ordinary matter and this might show up in particle accelerators as missing energy. But there’s only one accelerator powerful enough to spot em: the Large Hadron Collider at CERN which ain’t built yet, so we’ll have to wait a few years to observe direct evidence.

In the meantime, some astrotheorists are speculatin that unparticle stuff would have a significant effect on the physics of supernovas. So we might already have seen the effect of unparticles in our observations of explodin stars.

Steen “Ray” Hannestad and a few pals at the University of Aarhus in Denmark combed through the data on one famous event: SN1987a, the first supernova ever observed in action.

And the disappointing news is they ain’t seen nothing. Steen Ray reckons that supernova observations rule out the existence a large class of unparticle stuff.

The jury is still out, however. Supernova physics leaves open the possibility that unparticles might still rear their heads in other ways. But if Steen Ray is right, it ain’t quite as excitin’ as ya’ll had hoped.

Ref: arxiv.org/abs/0708.1404: Unparticle Constraints from SN1987A

The incredible galactic foxtrot

Thursday, August 30th, 2007

Ya’ll know the laws of physics are symmetrical–they have no preferred direction. The speed of light (and more or less everything else) is the same whichever way it is pointin’, right?

So it’d be surprisin’ if the universe turned out to be asymmetric, shockin’ if it had a prefered axis and stunnin’ if it had a direction in which things were different.

But it’s beginning to look that way. Two years ago, you could hear astro-jaws dropping all over the planet when a couple of upstarts suggested that data from a giant space-thermometer called the Wilkinson Microwave Cosmic Anisotropy Probe or WMAP looked as if it were aligned in a certain direction.

A-babblin and a-brayin, critics pointed out that the alignment matched the galactic co-ordinate system and so was probably an imprint of the Milky Way. Subtract this properly and the alignment would go away.

But it didn’t. And that left theorists a-scratchin their heads and a-rubbin their chins in amazement.

Now they gotta do a whole lot more a-broodin and a-worryin. Michael “Bongo” Longo at the University of Michigan has spotted another kind of alignment by a-meterin and a-measurin the orientation of 200,000 elliptical galaxies. That’s a lotta galaxies and it turns out they’re all aligned in the same direction too. We just ain’t noticed before now.

That’s put a ‘gator in the pool.

So what’s been causin this cosmic foxtrot? Ain’t nobody sure but we’re gonna be hearin a lot more about it in the weeks and months to come. Betcha!

Ref: arxiv.org/abs/0708.4013: The Axis of Opportunity: The Large-Scale Correlation of Elliptical Galaxies

Thursday’s haul

Thursday, August 30th, 2007

Today’s highlights from the physics preprint server:

Preventing Extinction and Outbreaks in Chaotic Populations

Working and Assembly Modes of the Agile Eye

The Beginning of String Theory: a Historical Sketch

The Conjunction Fallacy and Interference Effects

The physics of sandcastles

Thursday, August 30th, 2007

If ya’ll like a-splashin and a-paddlin at the seaside, ya know that wet sand is a different animal to dry sand. Nobody builds sandcastles outta dry sand, right?

Axel “Ice Cream” Fingerle and his buddy Stephan at the Max-Planck Institute for Dynamics and Self Organization in Germany say they know why.

“The reason…is that…small liquid capillary bridges form between
adjacent grains, exerting an attractive force upon
them by means of the surface tension of the liquids”

In other words, wet sand sticks together better. Now ya know!

Ref: arxiv.org/abs/0708.2597: Mechanisms of Dissipation in Wet Granular Matter

Human breath analysis

Wednesday, August 29th, 2007

Beware the early mornin’ kiss.

Yep, Jun “Eggy” Ye at JILA in Colorado has certainly taken this advice to heart. He’s gone and built himself a giant optical frequency comb laser capable zapping the bejesus out of any molecules found in human breath. When that happens the molecules absorb light producing a characteristic spectrum that allows their identification.

But the cool thing about the optical frequency comb technique is that it allows the simultaneus detection of thousands of molecules in real time. That makes it much better at identifyin’ stuff than either the electronic noses we been hearin about, which have a limited repertoire of stuff they can see, or mass spectroscopy which takes justabout forever to do its thing.

All kindsa things show up in human breath including markers for various types of cancer, such as ethane (which may be what these animals are spotting when they identify cancer victims). So being able to analyse breath quickly is a big deal.

But ain’t frequency comb lasers about the size of small factories? Won’t be easy fittin’ one of them into yer early morning bathroom routine

Ref: arxiv.org/abs/0708.3205: Human Breath Analysis via Cavity-enhanced Optical Frequency Comb Spectroscopy

Sequencing your DNA

Tuesday, August 28th, 2007

We done one human genome. Now we gotta do everyone’s.

So everybody and his cat is a-huntin and a-searchin for a way to sequence individual human genomes cheaply and easily. And there ain’t no shortage of ideas which makes it hard to keep up.

Thankfully ya don’t need to cos Massimiliano “Di” Di Ventra at the University of California, San Diego has done it for us.

His take on up ‘n’ comin DNA sequencing techniques is a fine overview of an important emerging topic. Miss this at your peril cos one day, one of these techniques is gonna sequence your own genome. Betcha!

Ref: arxiv.org/abs/0708.2724: Physical Approaches to DNA Sequencing and Detection

Could the Pioneer anomaly have a gravitational origin?

Monday, August 27th, 2007

Nope.

Ref: arxiv.org/abs/gr-qc/0602089: Could the Pioneer Anomaly have a Gravitational Origin?

Boron buckyballs

Monday, August 27th, 2007

A bit of hellraisin’ on a Friday night don’t do nobody no harm so it’s no surprise to see them chemists going at it hammer ‘n tong. Makes ‘em seem almost human.

The barney is over the shape of a molecule (might have guessed, right?).

Earlier this year, Nevill “Eye Test” Szwacki at Rice University in Texas dreamt up a new kinda buckyball made outta boron atoms rather than carbon. Szwacki reckons B-80 looks just like the carbon footballs y’all familiar with, ‘cept they have an extra atom at the centre of each hexagonal face.

Now Arnout “White coat” Ceulemans at the University of Leuven in Belgium has studied the structure using quantum chemical calculations and says that it ain’t football-shaped after all. Instead the ball is puckered, as if somebody let the air out.

Nobody has actually made B-80 and it might be a while before the matter is settled: after carbon footballs were first dreamt up, it took 20 years for somebody to actually synthesize one.

Ref: arxiv.org/abs/0708.2331: The Boron Buckyball has an Unexpected Th Symmetry

When gamma rays strike

Sunday, August 26th, 2007

On 6 January earlier this year, one of the strongest thunderstorms in livin’ memory a-crashed and a-roared its way across the Sea of Japan, rattlin the daylights outta the Kashiwazaki-Kariwa nuclear power plant on the coast.

This power plant is fitted with one of the most advanced radiation detectors on the planet and durin’ the storm it collected some extraordinary data. After a lil number crunchin, a team of physicists led Kazuo “Tiger” Makishima at the Cosmic Radiation Lab RIKEN, are publishing details of what they saw.

That night the nuclear power station was bombarded with gamma rays with energies of at least 10 MeV (that was the limit of the detectors).

Now gamma rays bursts ain’t commonly detected on the ground cos they ain’t easy to make (if you spot any it’s a good sign your local nuclear power station ain’t workin properly. It’s also why n-plants have the kit to detect ‘em) .

The RIKEN team says the gamma rays were probably caused by the sudden deceleration of high energy electrons as they smashed into atoms in the thunderclouds above, forcing the electrons to given up their energy in the form of gamma ray photons. But how did the electrons get accelerated to energies of 10 MeV or higher?

That’s a bit of mystery cos our ground-based accelerators require a near perfect vacuum to get particles a-movin and a-groovin at any kinda decent energy. Without a vacuum, particles start a-crashin and a-bangin into atoms and molecules in the air before they can get going.

Thunderclouds are known to have hugely powerful electric fields of more than 400 kiloVolts per meter so getting to 10 MeV from scratch requires quite a few metres of acceleration.

Unless the electrons start off with a fairly high energy, that is. The RIKEN team speculates that the gamma ray bursts in the thunderstorm were triggered by cosmic rays– high energy particles from outta space that come a-smashin and a-bargin their way through the atmosphere, creatin a shower of energetic electrons in their wake, a well known phenomenon.

So it’s quite possible that high energy electrons were created by a cosmic ray shower in the thundercloud and then accelerated to even higher energies by the electric field.

That seems to be backed up, at least in part, by the fact that the gamma ray bursts did not occur at the same time as visible lightning strikes so the mechanism behind that kinda discharge don’t seem to be responsible.

Fascinatin’ stuff, huh?

Ref: arxiv.org/abs/0708.2947 :D etection of High-Energy Gamma Rays from Winter Thunderclouds