the physics arXiv blog

Hafnium ‘n’ hafnotium

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

A Limiting Rule for the Variability of Coding Sequence Length in Microbial Genomes

High-Sensitivity Diamond Magnetometer with Nanoscale Resolution

Parity-Violating Macroscopic Force between Chiral Molecules and Source Mass

Statistics of Multiphoton Events in Spontaneous Parametric Down-Conversion

Neutrinos from active black holes, sources of ultra high energy cosmic rays

Evidence of Phonon-assisted Tunnelling in Electrical Conduction through DNA Molecules

Pedestrian Flow at Bottlenecks

Does Avian Magnetoreception Rely on Both Magnetite and Maghemite?

Posted in Cherry pickin' | No Comments »

How orbiting electrons can lengthen nuclear half-life

Nuclear fission is the process in which a nucleus decays into two fragments. For large nucleii, this process is a complicated one in which the nucleus undergoes several stages of deformation before tearing itself apart.

In recent years, physicists have predicted that fission ought to be affected by the presence of electrons in orbit about the nucleus. That’s because any change in the shape of the nucleus naturally affects the electrons which tend to absorb energy making fission less likely. And the more electrons there are, the more energy they absorb. But the effect has never been observed because ordinary, naturally ocurring elements simply don’t have enough electrons to make this effect significant.

Today, Vlad Dzuba and Vic Flambuam at the University of New South Wales in Australia have calculated the strength of this effect for superheavy elements which would have more electrons. They say that although the effect is tiny for naturally ocurring nuclei with fewer than 100 or so protons, it would be hugely significant for these larger nuclei. In fact, they calculate that an atom with 160 protons would have double the expected half life because of this effect.

That could have significant implications for how much of this stuff we’re likely to find because elements that decay quickly tend to be rarer) . Last week, arxivblog reported on the potential discovery of element 122 (with 122 protons). Perhaps the groups looking for superheavies should be setting their sights much, much higher.

Ref: arxiv.org/abs/0805.1961: The Effect of Atomic Electrons on Nuclear Fission

Posted in Sparks 'n' thunderbolts, Fightin' | No Comments »

How ESA plans to search for other Earth’s

We’re getting close to the day when we’ll spot an Earth-like planet orbiting another star. Astronomers have already seen a number of superEarth candidates–rocky planets in the habitable zone that are many times larger than Earth. They’ve even begun to analyse the atmosphere of these places and got some idea of what it might be like on their surfaces. Earth-sized planets won’t be far away now.

But if we are to spot the signs of life on these bodies, what should we look for? The European Space Agency has been giving this some serious thought for a mission called Darwin currently pencilled in for launch in 2015. It’s goal is to look for signs of life on Earth-like planets.

Today, the team behind the mission explain some of the reasoning behind their design for the spacecraft. To look for life, they’ve had to make some important assumptions about the form it might take. For example, they’re plumping for carbon-based life forms that rely on water as a solvent. Fair enough but their assumptions go a lot further:

“We assume that extraterrestrial life is similar to life on Earth in its use of the same input and output gases, that it exists out of thermodynamic equilibrium, and that it has analogs to microorganisms on Earth.”

That’s getting pretty specific but they say their hand is forced by the fact that they’ve never seen any other type of life and so can’t possibly know what else to look for.

So Darwin will look for carbon dioxide, ozone and of course water in the atmospheres of these planets as well as methane and ammonia.

Finding those in the right abundances will be good evidence that something interesting is happening on these planets although finding any other gases that are out of geochemical equilibrium will also be an eye-opener.

The trouble is that finding these signatures will by no means be a slam dunk in favour of life.

In one of the classic scientific papers of the 20the century, Carl Sagan and colleagues published their analysis of the data from the Galileo spacecraft’s 1990 flyby of Earth. The spacecraft saw all those gases and more. Their conclusion? “Our results are consistent with the hypothesis that widespread biological activity exists…on Earth”.

Not quite conclusive and that’s from a distance of a thousand kilometres. So it’s hard to imagine that data from Darwin could provide conclusive evidence of life at a distance measured in dozens or hundreds of lightyears. But I guess that’s nothing a good PR team couldn’t solve.

Ref: arxiv.org/abs/0805.1873: Darwin – A Mission to Detect, and Search for Life on, Extrasolar Planets

Posted in Slimey stuff, Stars in their eyes | 3 Comments »

Phobos could form Saturn-like ring around Mars

The martian moon Phobos is spiralling towards Mars at a rate of 20 cm a year. (That compares with our own moon which is spiralling away from us at about 4cm per year).

The question is when will it hit. On the arxiv today, Bijay Kumar Sharma calculates that we have about 11 million years before it smashes in to the Red Planet. That’s plenty of time to visit although he also points out that Phobos may break up long before that because of tidal forces. If that’s going to happen it’ll probably occur about 7 million years from now.

But it’s not all bad news. Sharma says if tidal forces get the better of Phobos, it should form a Saturn-like ring around Mars. Now that would be worth seeing.

Ref: arxiv.org/abs/0805.1454: Theoretical Formulation of the Phobos, moon of
Mars, rate of altitudinal loss.

Posted in At the seaside, Secrets | No Comments »

World’s oldest social network reconstructed from medieval land records

The network of links between peasants who farmed a region of small region of south west France called Lot between 1260 and 1340 have been reconstructed by Nathalie Villa from the Universite de Perpignan in France et amis.

The team took their data from agricultural records that have been preserved from that time. This is a valuable dataset because it records the date, the type of transaction and the peasants involved.

Villa and co used this to recreate the network of links that existed between individuals and families in th 13th and 14th centures in this part of France. They then drew up a self organising map of the network (see above).

But the best is surely to come. What Vilal hasn’t yet done is analyse the network’s properties. Does this medieval network differ in any important ways from the kind of networks we see between individuals in the 21st century? If so, what explains the differences and if not what are the invariants that link our world with 13th century France. The team promises an analysis in the near future.

In the meantime, it’s worth reflecting on the significance of this work. These kinds of networks could provide anthropolgists with an exciting new way to study historical societies.

And while this may be the world’s oldest social network (if anyone knows of an older network, let us know), it’s unlikely to remain so for long. Excellent records survive of transactions in ancient Rome, from the earlier Greek empire and even from the Egyptian civilizations that built the pyramids some 4000 years ago.

If Villa work turns up any useful insights into the nature of medieval society in France, you can be sure that anthroplogists will rush to repeat the method usnig data from from even older societies.

All that’s left is to christen the new science of the study ancient social networks Any suggestions?

Ref: arxiv.org/abs/0805.1374: Mining a Medieval Social Network by Kernel SOM and Related Methods

Posted in Nets 'n' webs, Calculatin', The good ol' days | 1 Comment »

Speech therapy revolutionised by hi-tech dentures

Dentures rarely find their place at the cutting edge of science (some say unfairly) but today is an exception.

Christophe Jeannin at the Institut de la Communication Parlée in Grenoble, France, and a few pals have developed a set of hi-tech dentures that contain a number of tiny pressures sensors that record the position of the tongue and the force it applies during speech.

That’s important because nobody has ever accurately measured that behaviour of the tongue during speech which is a serious impediment to the development of computer models of humans speech, which in turn makes it harder to perfect robot speech and various kinds of computerised speech therapy.

Jeannin and friends place to change that and have even recruited 20 denture wearers to try out the device (they each had their own personalised set of pressure sensitive dentures rather than having to take turns on the same set).

Just one problem however: are the speech patterns of denture wearers really the same as those with a full set of clappers? Who knows?

But if they can work that out, researchers will have a good data set to chew on which they can use to determine the mechanics of tongue-tooth interaction during speech for the first time.

Ref: http://arxiv.org/abs/0805.0744: Tongue Pressure Recordings during Speech using Complete Denture

Posted in At the seaside, Fightin' | No Comments »

In case ya missed ‘em…

…the pearls from this week’s physics arXiv blog:

First evidence that water forms in interstellar space

Why tiny helicopters are so hard to fly

The puzzling discovery of a motor made from liquid film

Blind date gives astronomers a new love of the stars

The mathematics of tackling tax evasion

Posted in Highlights | No Comments »

Taxes ‘n’ tasters

The other highlights from the physics arXiv this week:

Fermi at Los Alamos and the Early Britain’s Way to Nuclear Energy

The Silencing of Neuronal Activity by Noise and the Phenomenon of Inverse Stochastic Resonance

Molecular Thin Films: a New Type of Magnetic Switch

No Many-Scallop Theorem: Collective Locomotion of Reciprocal Swimmers

Probing a Bose-Einstein Condensate with an Atom Laser

Search for Variation of the Fundamental Constants in Atomic, Molecular and Nuclear Spectra

To What Extent does Genealogical Ancestry imply Genetic Ancestry?

Posted in Cherry pickin' | No Comments »

The mathematics of tackling tax evasion

In recent years, economists have gained the luxury of actually being able to test their ideas in experiments involving the behaviour of real people. And one particularly new and promising area of experimental economics focuses on tax evasion, which ought to be of keen interest to many governments around the world.

A couple of years ago, Simon Gachter at the University of Nottingham carried out a number of experiments on the way people co-operate which had profound implications for tax evasion. Gachter’s conclusion was that people decide whether or not to pay taxes based on the behaviour of their peers. The implication is that in certain circumstances, tax evasion may be a kind of fashion that spreads through society like bell-bottomed jeans.

Today, Georg Zaklan from the University of Bamberg in Bavaria, Germany, and pals show just how this might work in the real world by constructing a model of tax evasion behaviour in society.

His society is an Ising spin model (most commonly used to show critical behaviour in magnetic materials) in which agents can chose to evade taxes or not based on the behaviour of their neighbours.

Sure enough, the model shows that without any control on tax evasion, the behaviour can spread rapidly, disappear equally quickly and re-appear again later (just like bell-bottoms).

But the beauty of Zaklan’s simulation is that it suggests a way in which governments can very easily prevent the spread of tax evasion. The team has modelled the effect of increasing the probability that a tax evader will be caught and show that a small increase could have profound effects on tax evasion.

So what governments should do is increase the number of tax audits they carry out (as well as making sure there are adequate punishments for offenders). Zaklan says the model implies that if only 1 % of the population is tax audited, tax evaders would be brought to heel for good.

That sounds interesting and might be worth a try in some countries, were it not for some important gaps in the paper.

The biggest of these is this: what evidence is there that tax evasion fluctuates in the real world in the way that the Ising model predicts? Zaklan doesn’t present any, so while this work is interesting, I’ll need some better evidence before I’m convinced that his model really describes what’s going on.

Ref: arxiv.org/abs/0805.0998: Controlling tax evasion fluctuations

Posted in Nets 'n' webs, Calculatin' | No Comments »

Blind date gives astronomers a new love of the stars

When it comes to studying the night sky, astronomers aren’t short of images. There are huge archives of both amateur and professional images taken in the the age before digital imaging. The Harvard College Observatory Astronomical Plate Stacks contain enough images to cover the entire sky 500 times over.

But although the image quality is excellent, the problem is the indexing. When logs go missing or when data has been badly transcribed, it can be almost impossible to work out exactly what appears in an image or when it was taken.

The error rate in many older collections is high enough to make astronomers think twice about using them. And as astronomy moves towards its goal of creating a Virtual Observatory, in which all images are available online in a kind of giant virtual planetarium, a lack of trust in the data is a serious problem.

If, as an astronomer, you’ve been losing sleep over this issue, you can rest easy. David Hogg at New York University and buddies (including the search giant Google), have solved the problem by reducing it to one of image matching.

They take an astrophotograph of dubious provenance and use a computer program called “Blind Date” to look for asterisms (the shapes that constellations make). When they find a match, this immediately locates the image within a part of the sky. But the really cool part of their technique is based on the fact that stars move over time, albeit by tiny amounts. So any small deviation in the location of stars within an image give an immediate time stamp for when the shot was taken.

The team says this technique works for every science-quality image that it has been tested against and 85 per cent of lower quality images. In some cases, it can date images to within a few months.

The plan is to use Blind Date to produce metadata automatically for every image that is entered into the Virtual Observatory, which should reduce errors substantially and also prevent deliberate spoofing of the project.

That should go a long way to restoring trust.
Ref: arxiv.org/abs/0805.0759: Blind Date: Using Proper Motions to Determine the Ages of Historical Images

Posted in Stars in their eyes | No Comments »