Archive for the ‘Secrets’ Category

Important changes to the Physics arXiv Blog

Sunday, March 15th, 2009

From Monday 13 March, the Physics arXiv Blog will appear exclusively on technologyreview.com

This is an exciting move for the blog because it will allow me to concentrate on reading and filtering the fantastic ideas on the arXiv while leaving the increasingly onerous task of administering a popular website to the talented tech guys at TR.

If all goes smoothly, your RSS feeds and email subscriptions will be transferred seemlessly to our new hosts. And if it doesn’t go smoothly, let us know. We’ll be working hard to iron out any teething problems as soon as we can.

The new URL is:  arxivblog.technologyreview.com

I hope you’ll join me.

Kentucky

The secret of world class putting

Friday, March 13th, 2009

perfect-putting

Watch professional golfers putt and you’ll eventually notice three common features about their style,  says Robert Grober, an expert on the physics of golf at the Yale University.

First, the putter head always moves at a constant speed when it hits the ball. Second, the length of time the putting stroke takes has little impact on the speed of the ball (and therefore the length of the putt). And finally, a professional golfer’s backswing takes about twice as long as the  downswing.

Grober has used these observations to construct a mathematical model of a putting swing and to explore other properties of such a system.

It turns out that the model that best accounts for this behaviour is a simple pendulum driven at twice its resonant frequency.

That explains a number of other observations about professional golfers, says Grober. For example, a common putting tip is that longer backswings equate to longer putts. This model has exactly this characteristic: the length of the backswing is proportional to the speed of the club at impact.

It is also relatively straightforward to get a sense of the tempo of the required putt by swinging the club back and forth in resonance, like a pendulum. The duration of the actual stroke is exactly half the length of the putter cycle (i.e. from the address position moving backward, to the address position moving forward). “In fact, one often observes golfers instinctively doing this before they hit a putt,” says Grober.

So now the secret is out. Make a careful note for next time you’re out on the links.

Ref: arxiv.org/abs/0903.1762: Resonance in Putting

Why spiders’ silk is so much stronger than silkworms’

Friday, February 27th, 2009

silk-structure

Spider silk and silkworm silk are almost identical in chemical composition and microscopic structure. And yet spider silk is far tougher. “One strand of pencil thick spider silk can stop a Boeing 747 in flight,” say Xiang Wu and colleagues at the National University of Singapore. Whereas a pencil thick strand of silkworm silk couldn’t. Why the difference?

Xiang and co say they’ve worked out why by successfully simulating the structure of both silks for the first time. Both spider silk and silkworm silk are made up of long chains of amino acids called polypeptides and are particularly rich in the amino acids alanine and glycine.

Various imaging techniques have shown that the sequences of amino acids differ slightly between spide and silkworm silk but this alone cannot explain the huge difference in strength, says Xiang.

Instead, the secret appears to lie in the way polypeptide chains fold into larger structures. Xiang’s model shows that a subtle difference exists between the silks in structures called beta sheets and beta crystallites. This insight has allowed the team to model for the first time the way in which both silks break.

That’s important because being able to predict the mechancial properties of an organic material simply by studying its structure is going to be increasingly useful. It may even allow us to take a better stab at making spider-like silk synthetically for the the first time.

Anybody with a 747 watch out.

Ref: arxiv.org/abs/0902.3518: Molecular Spring: From Spider Silk to Silkworm Silk

Simulating Sweden

Tuesday, February 10th, 2009

sweden

If you want to model how infectious diseases spread, you need a decent simulator to see how the various coping strategies pan out. Your simulation needs to take into account the population, its age and gender distribution, where people live and how far they travel from home to work and which people share homes.

But making this data realistic would be hard. After all, would anybody willingly agree to have their real data entered into such a simulation?

Actually yes. Swedes. All nine million of them.

Yep, the personal details of the entire Swedish population have been used to create what must be the world’s largest and most realistic computer simulation of the way infectious diseases spread.

Lisa Brouwers at the Swedish Institute for Infectious Disease Control and buddies have built a simulation called Microsim in which every member of the Swedish population is represented with details including their sex, age, family status, school, workplace and their geographic location at these places to within 100 metres.

That makes for potentially fantastic simulations but it also raises extraordinary questions over privacy. The data is only minimally anonymized: each individual is given a random identifier but otherwise their personal data is intact.

Given that the team is combining data from three different sources, this doesn’t sound like nearly enough protection.

But Brouwers must know what she’s doing. Or at least be praying that the rest of Sweden doesn’t find out what she’s done.

Ref: arxiv.org/abs/0902.0901: MicroSim: Modeling the Swedish Population

Challenging the nature of black holes

Wednesday, February 4th, 2009

black-hole-formation

The nature of black holes has puzzled physicists for decades. But while the debate has fizzled in recent years, some new thinking is about to set it alight again.

Black holes are fundamentally a product of general relativity, which allows for a gravitational collapse so violent that no other force can oppose it. When that happens, the collapse continues until the density of matter becomes infinite and gravity becomes so strong so as to prevent even light from escaping. This generates an “event horizon”, a volume of space around the black in hole inside whihc events cannot affect an outside observer.

But perhaps there’s more to it than that, suggest Matt Visser at Victoria University of Wellington in New Zealand and pals who ask whether quantum processes can have an affect on the collapse of a star.

It’s fair to say that the consensus among astrophysicists is that quantum physics can be safely ignored when considering the collapse of a star. As Visser and co put it: “There is a widespread feeling in the general relativity community that semiclassical quantum back-reaction effects are always small, and never enough to significantly alter the classical picture of collapse to a black hole.”

But Visser and pals beg to differ. The standard thinking is that if an event horizon forms, then quantum field theory is well behaved there. But that makes the assumption that am event horizon will form.

Visser and co say this may not be a valid assumption and go on to show how the vacuum energy might stifle the formation of an event horizon.

What does this mean for black holes? What Visser and co end up with is something very similar to a black hole but without an event horizon–a black hole mimic, they say.

Debating the nature of black holes is a well trodden path. But what’s interesting is that numerous avenues of thought–from loop quantum gravity to abstract studies of the nature of horizons–are now hinting at something more subtle and interesting about the nature of star collapse.

Black holes might never be the same again.

Ref: arxiv.org/abs/0902.0346: Small, dark, and heavy: But is it a black hole?

Fermi’s paradox solved?

Monday, February 2nd, 2009

ets-in-range

We have little to guide us on the question of the existence intelligent life elsewhere in the universe. But the physicist Enrico Fermi came up with the most obvious question: if the universe is teeming with advanced civilizations, where are they?

The so-called Fermi Paradox has haunted SETI researchers ever since. Not least because the famous Drake equation, which attempts put a figure on the number intelligent civilisations out there now, implies that if the number of intelligent civilisations capable of communication in our galaxy is greater than 1, then we should eventually hear from them.

That overlooks one small factor, says Reginald Smith from the Bouchet-Franklin Institute in Rochester, New York state. He says that there is a limit to how far a signal from ET can travel before it becomes too faint to hear. And when you factor that in, everything changes.

Smith uses this idea to derive a minimum density of civilizations below which contact is improbable within a given volume of space. The calculation depends on factors such as the lifetime of a civilization and the distance that it might be possible to communicate over and it produces some interesting scenarios:

Assuming the average communicating civilization has a lifetime of 1,000 years, ten times longer than Earth has been broadcasting, and has a signal horizon of 1,000 light-years, you need a minimum of over 300 communicating civilization in the galactic neighborhood to reach a minimum density.

So if there are only 200 advanced civilizations in our galaxy, the chances are that they’ll never notice each other.

Of course, we’ve no way of knowing how many advanced civilizations are out there. But this kind of thinking could, for the first time, put a limit on the number that could be out there: less than 200 perhaps?

It also has significant implications for Fermi’s line of thinking.

Would it be too early to say the paradox has been solved?

Ref: arxiv.org/abs/0901.3863: Broadcasting But Not Receiving: Density Dependence Considerations for SETI Signals

Is meditating good for the heart?

Thursday, January 29th, 2009

heart-beat-intervals

Let’s calm things down with some deep breaths: in…out…in…out. Relax. Feel your pulse rate slowing?

We’ve known for some time that there’s more to pulse rate than beats per minute. Heart rate variability–the change in intervals between beats–can be used to distinguish healthy hearts from diseased and damaged ones.

One sign of a healthy heart is slight, seemingly random variations in the intervals between beats. These variations seem to be governed by power laws which is somewhat of a puzzle in itself.

By contrast, a steady unchanging beat interval seems to be a sign of disease.

Now Nikitas Papasimakis and Fotini Pallikari at the University of Athens in Greece have studied the heart beat intervals in people who are meditating and found that the power law variations disappear.

That raises an interesting question: is meditating good for the heart or not? Papasimakis and Pallikari argue that the loss of power law correlations cannot be used as evidence of ill health because the correlations return as soon as the subject stops meditating. Fair enough.

But what does the ability to switch these correlations on and off mean for health? Nobody knows just yet but it’s  a fascinating area in which it’ll be interesting to see  where more data leads.

Ref: http://arxiv.org/abs/0901.4295

: Breakdown of Long-Range Correlations in Heart Rate Fluctuations During Meditation

How Google’s PageRank predicts Nobel Prize winners

Wednesday, January 21st, 2009

pagerankings-graph

Ranking scientists by their citations–the number of times they are mentioned in other scientists’ papers– is a miserable business. Everybody can point to ways in which this system is flawed:

  • not all citations are equal. The importance of the citing paper is a significant factor
  • scientists in different fields of study use citations in different ways. An average paper in the life sciences is cited about six times, three times in physics, and about once in mathematics.
  • ground-breaking papers may be cited less often because a field is necessarily smaller in its early days.
  • important papers often stop being cited when they are incorporated into textbooks

The pattern of citations between papers forms a complex network, not unlike the one the internet forms. Might that be a clue that point us towards a better way of assessing the merits of the papers that it consists of?

(more…)

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…)

I know why the phase-locked wineglass sings

Thursday, January 8th, 2009

singing-wineglasses

Here’s a neat party trick to impress your friends.

Rub your finger around the rim of a wineglass and friction causes it, and any liquid it contains, to oscillate. When this vibration produces an audible pure tone, the wine glass is said to “sing”.

Now Ana Karina Ramos Musalem and pals at the Weizmann Institute of Science in Israel have shown how to couple one singing wineglass to another so the second wineglass sings without anybody touching it.

The trick is to place both wineglasses in a sink of water (without the water overflowing into the glasses).  Rubbing one so that it sings should make the other sing too. This  phenomenon is known as phase-locking and is also responsible for populations of crickets that chirp together and fireflies that flash together.

Phase locking depends on the strength of the coupling. This is greatest when the glasses are closer together and when their resonant frequency is similar. So if you run into trouble, try moving them nearer to each other and matching their frequencies by changing the amount of water in each glass.

Then watch as jaws drop around the dinner table.

(With apologies to Maya Angelou.)

Ref: arxiv.org/abs/0901.0656: Phase locking between two singing wineglasses