Archive for the ‘At the seaside’ Category

Why SETI will have missed any cost conscious ET civilizations

Friday, October 24th, 2008


If we want to contact any of those other civilizations out there, we’ll need a beacon to send messages with. But what to build?

Gregory Benford at the University of California Irvine and family (?) have done a cost/benefit analysis on the types of microwave generators out there that can produce the 10^17 W necessary to reach a significant proportion of the galactic habitable zone.

There are various ways that the cost can be optimised and the Benfords summarise them like this:

“Thrifty beacon systems would be large and costly, have narrow searchlight beams and short dwell times when the Beacon would be seen by an alien observer at target areas in the sky. They may revisit an area infrequently and will likely transmit at high microwave frequencies, ~10 GHz. The natural corridor to broadcast is along the galactic spiral’s radius or along the spiral galactic arm we are in.”

This has implications for the search for ET civilisations (as opposed sending messages for them). If ET civilisations are as cost conscious as we are,  then they may well have built beacons in this way.
And if so, say the Benfords, nearly all SETI searches to date would have missed them.

Ref: Cost Optimized Interstellar Beacons: METI Cost Optimized Interstellar Beacons: SETI

Frustration with fluid dynamics

Thursday, October 23rd, 2008

There is no shortage of fascinating videos for the Gallery of Fluid Motion at the upcoming meeting of the American Physical Society Fluid Dynamics division.

At least they sound interesting. We’ll never know because they’re practically impossible to download from eCommons library at Cornell University. That’s not good enough.

Surely YouTube (or one of its cousins) would be a better way to display these videos quickly, easily and above all reliably.

By all means place a hi-res version on the eCommons library for whoever has the patience to download it, but spare a thought for the rest of us. Spread the lurv, is all I’m saying. There’s plenty to go round.

Here’s a list of just a few of the interesting-sounding videos on the arXiv. If you’re thinking of downloading any, good luck.

Dynamics of Water Entry

The Bounce-Splash of a Viscoelastic Drop

Tornadoes in a Microchannel

Liquid acrobatics

The Clapping Book

Atoms in the Surf

Update: Turns out the videos are already on YouTube (see comments). Doh! (Might have been useful to mention this in the papers.)

Thanks Sheila!

The neglected puzzle of low energy nuclear reactions

Friday, October 10th, 2008


Cold fusion won’t go away and perhaps rightly so. Numerous groups have reported idiosyncratic behaviour of palladium hydrides sitting in heavy water when a current passes through them. Many of these experiments are said to be repeatable.

Of course, serious questions remain over what exactly is going on in these experiements. They may or may not involve fusion but either way, something interesting will have to be dreamt up to explain many of the results.

These days cold fusion goes by the name of LENR (low energy nuclear reactions). And Allan Widom from Northeastern University in Boston and a couple of mates have taken the trouble to spell out how they think the electroweak force may be behind one class of these reactions.

They say that the well known decay of a neutron into a proton and an electron is mediated by the electroweak force. And that the reaction can be reversed to turn electrons and protons into neutrons, a process that would also result in nuclear transmutation, which in turn my be responsible for the release of excess heat and of nuclear by-products. Both of these things are claimed to be seen in LENR experiments.

Surely it’s time we bury the hatchets on this one and start working out exactly what is going on in LENRs. No?

Ref: A Primer for Electro-Weak Induced Low Energy Nuclear Reactions

The remarkable language of Vai

Monday, October 6th, 2008


Vai is a language spoken by 150,000 people in western Africa, specifically in Liberia and Sierra Leone. The language is noteworthy because its uses a remarkable system of sounds. Speakers must be able to pronounce seven oral vowels, five nasal vowels and 31 consonants all of which come in various combinations. In its written form, Vai has 229 characters.

So perhaps it wouldn’t be surprising if Vai had some interesting statistical characteristics not shared by other languages. If so, that might give some insight into the language’s unique history and evolution. This week, Charles Riley at Yale University and a few pals make exactly that claim.

Their analysis focuses on the the written form of Vai and the complexity of the characters in its alphabet. The complexity of a character is a measure of how difficult it is to draw. For example, the letter ‘O’ consists of two arches connected by two line sections which, using the strange arithmetic of character complexity, gives it a complexity of 8. The letter ‘X’ which is two straight lines that cross, has a complexity of 7.

By contrast, most characters in Vai have a complexity of more than 20 and one letter has a complexity of 48.

In all languages analysed to date, the complexity of characters is governed by an overarching rule which is that it is uniformly distributed. That means that there should be roughly equal numbers of characters with similar complexities. That’s true whether the language be Latin, Cyrillic and Runic scripts.

But Vai turns out to be different, says Riley and co. The complexity of the Vai alphabet is a better fit to a Poisson distribution rather than a uniform distribution.

So does that mean there is something special about Vai that sets it apart from other languages?

Maybe. The authors say non-uniform complexity is probably the result of the way the language was first written down in the mid-19th century. Riley and co suggest that this may have been influenced by a Cherokee native American who lived in an American mission in the area at the time.

Cherokee was famously first written down by a tribesman named Sequoyah who had seen western script without knowing what it mean. He then wrote out a similar looking script in which each sign represented a Cherokee syllable.

The clear, if improbably, implication by Riley and pals is that Vai was written down in the same way.

There are two problems with this analysis. First, as far as I know, Cherokee has not been subjected to this kind of analysis. If it has a uniform distribution, this idea is scuppered.

Second, what the authors fail to take into account is that although the alphabet has 229 characters, there is a large amount of redundancy and only 100 or so are in common usage.

When the analysis is redone using only these common characters, I wouldn’t mind betting that a uniform distribution of complexity emerges.

Which means that Riley and co have a little work to do before they take their analysis of Vai any further down this little backwater of linguistics

Ref: Distribution of Complexities in the Vai script

Forget black holes, could the LHC trigger a “Bose supernova”?

Monday, September 29th, 2008


The fellas at CERN have gone to great lengths to reassure us all that they won’t destroy the planet (who says physicists are cold hearted?).

The worry was that the collision of particles at the LHC’s high energies could create a black hole that would swallow the planet. We appear to be safe on that score but it turns out there’s another way in which some people think the LHC could cause a major explosion.

The worry this time is about Bose Einstein Condensates, lumps of matter so cold that their constituents occupy the lowest possible quantum state.

Physicists have been fiddling with BECs since the early 1990s and have become quite good at manipulating them with magnetic fields.

One thing they’ve found is that it is possible to switch the force between atoms in certain kinds of BECs from positive to negative and back using a magnetic field, a phenomenon known as a Feschbach resonance.

But get this: in 2001, Elizabeth Donley and buddies at JILA in Boulder, Colorado, caused a BEC to explode by switching the forces like. These explosions have since become known as Bose supernovas.

Nobody is exactly sure how these explosions proceed which is a tad worrying for the following reason: some clever clogs has pointed out that superfluid helium is a BEC and that the LHC is swimming in 700,000 litres of the stuff. Not only that but the entire thing is bathed in some of the most powerful magnetic fields on the planet.

So is the LHC a timebomb waiting to go off? Not according to Malcolm Fairbairn and Bob McElrath at CERN who have filled the back of a few envelopes in calculating that we’re still safe. To be doubly sure, they also checked that no other superfluid helium facilities have mysteriously blown themselves to kingdom come.

“We conclude that that there is no physics whatsoever which suggests that Helium could undergo
any kind of unforeseen catastrophic explosion,” they say.

That’s comforting and impressive. Ruling out foreseen catastrophies is certainly useful but the ability to rule out unforeseen ones is truly amazing.

Ref: There is no Explosion Risk Associated with Superfluid Helium in the LHC Cooling System

Why spontaneous traffic jams are like detonation waves

Wednesday, September 24th, 2008


We’re all familiar with phantom jams, traffic blockages that arise with no apparent cause and that melt away for no discernible reason.

Today Ruben Rosales and pals at MIT and the University of Alberta in Canada coin a new term for the waves that cause these hold ups: they call them jamitons.

And jamitons turn out to have an interesting property: they are self-sustained disturbances consisting of a shock matched to vehicle speed.

If that sounds familiar, it’s because you’re reminded of the way in which certain types of transonic disturbances can be self-sustaining. In the world of a chemists, these are known as detonation waves.

Rosales and co say jamitons and detonation waves are mathematical analogues.

That sounds interesting and useful and perhaps one day it will be. But you wouldn’t guess it from this paper.

Rosales and friends are unable to run with their analogy in any useful way. They say that the existence of jamitons in traffic flow are an indication that dangerous vehicle concentrations may occur (no, really?).

And they conclude: “such situations may be avoided by judicious selection of speed limits, carrying capacities, etc” (Wow!)

In other words, spontaneous traffic jams may cause avoidable crashes. Nothing gets past these guys.

Ref: On “Jamitons,” Self-Sustained Nonlinear Traffic Waves

A short history of computer art in Soviet bloc countries

Friday, September 5th, 2008


Many of us think of little else than the history of computer art in former Soviet bloc countries and today our prayers are answered in the form of a curious paper that examines just this topic.

The paper says that the Soviet bloc country most advanced in this respect appears to have been Yugoslavia. The author, Eric Engle,  focuses on the role of computer art in the New Tendencies movement that grew up in and around Zagreb the late 1960s and early 70s in Yugoslavia.

Why was Yugoslavia the most advanced? One important factor that Engle identifies is the extent to which Soviet bloc countries embraced capitalism, which gave them access to more advanced western computers.

For various reasons, Yugoslavia was more open to the west than say East Germany or the USSR  and so its computer art became more advanced.

Ref: Computer Art in the (Former) Soviet Bloc

The sound of a bouncing basketball

Wednesday, August 27th, 2008


“A basketball bounced on a stiff surface produces a characteristic loud thump, followed by high pitched ringing,” says Joanthan Katz at Washington University in St Louis.

The question is why and, conveniently, Katz provides the answer on the arXiv today.

He assumes first that a basketball is an inextensible but perfectly flexible hollow sphere.

From this, he calculates that the thump is the result of the change of shape of the ball as it deforms when hitting a hard surface.

This creates a monopole source of sound that goes through only one full cycle of its frequency (of about 82 Hz for a full-sized basketball), hence the dull thump.

The ringing is caused by what Katz calls a dipole emission of sound and is essentially the vibration of the air within the basketball after the impact.

That’s a neat bit of calculating and Katz is honest to fault when it comes to pointing out the weaknesses of his model. He says, for example, that while the assumption of intextensibility is reasonable, perfect flexibility is a vast simplification that is necessary to make the problem tractable.

However,  he says assuming the opposite–that the ball has an extensible membrane and an incompressible filling fluid–produces neither a thump nor a ring.

If you’ve ever dropped a balloon filled with water, you’ll know what he means.

Ref: Thump, Ring: the Sound of a Bouncing Ball

The puzzling beauty of Abelian sandpiles

Friday, August 15th, 2008


Pour real sand, a grain at a time, onto a flat surface and the result is a rather dull pyramidal shape. but in the mathematical world, the result is a little  different.

The image above is produced using a theoretical model called an Abelian sandpile model. It is  produced by dropping some 200,000 grains onto a single point on flat grid and distributing them according to a set of toppling rules.

For example, a point on the grid can hold no more than three grains. If a fourth lands, all the grains are redistributed, avalanche style, to surrounding points.

This is a relatively new discipline–Abelian sandpile models were only discovered in 1990 by Deepak Dhar at the Tata Institute of Fundamental Research in Mumbai, so people are still trying to characterise them.

This pattern was produced Dhar and colleagues who are obviously captivated by its beauty and complexity but puzzled by how to analyse it. They say that simpler, related patterns seem to have an eightfold symmetry. But this one has them stumped.  “It has not been possible to characterize [this pattern] so far,” they say.

That looks like an interesting puzzle. There’s work here for anyone who needs it.

Ref: Pattern Formation in Growing Sandpiles

Deconstructing DiMaggio’s 56-game hitting streak

Monday, August 4th, 2008


“The incredible record of Joe DiMaggio in the summer of 1941 is unparalleled. No one has come close—before or since—to equaling his streak of hitting safely in 56 games in a row.”

So begin Steve Strogatz and Sam Arbesman from Cornell University in their paper discussing the likelihood of DiMaggio’s record.

“People have…stated that it is the only record in baseball (or perhaps even in all of sports) that never should have happened, statistically speaking: while other records can be explained by expected outliers over the long and varied history of professional baseball (nearly 150 years), DiMaggio’s record stands alone”

But as with so many statistical assumptions, a proper analysis can reveal counterintuitive results, say Strogatz and Arbesman. The pair have modelled the phenomenon of hitting streaks using a number of simple models and guess what…DiMaggio’s record is not as unexpected as it looks.

The models suggest that while a DiMaggio-like record is unlikely in any given year, it is not unlikely to have occurred about once within the history of baseball.

But having plugged the statistical performance of a number of players into the model, DiMaggio is not the most likely to have picked up such a record. That honour goes to one of Ross Barnes, Willie Keeler or Hugh Duffy (there is no single most likely player). DiMaggio, it turns out, is 47th most likely player to have reached the record in one of the models used.

More curious is why Strogatz, widely considered to be the father of the small world network theory, has taken up the baton in examining baseball statistics. He joins a small but select group of physicists and mathematicians with a passion for the game including Gene Stanley and Percy Diaconis.

So what’s next? Surely the task now is to find a record that defies statistics in the sense that it is truly unlikely. Let me be the first to suggest Don Bradman’s 99.94 batting average in test cricket.

Ref: A Monte Carlo Approach to Joe DiMaggio and Streaks in Baseball