arXiv_blog

In a deadly flu outbreak, shutting airports should reduce the spread of the disease. But networks scientists have discovered a better approach that's just as effective.






One of the nightmare scenarios for modern society is the possibility of a global flu pandemic like the 1918 Spanish influenza which infected about a quarter of the global population and killed as many as 130 million of them.



An important question for policy makers is how best to limit the spread of such a disease if a new outbreak were to occur. (The Spanish flu was caused by the H1N1 flu virus that was also responsible for the 2009 swine flu outbreak.)



One obvious idea is to close international airports to prevent, or at least dramatically reduce, the movement of potentially infected individuals between countries. But is this the best approach?



Today, Jose Marcelino and Marcus Kaiser at Newcastle University in the UK, provide an answer. They say a better approach is to cut specific flights between airports because it can achieve the same reduction in the spread of the disease with far less drastic action.



These guys used a standard disease-spreading model to simulate the spread of an H1N1-type infection across a network consisting of the world's top 500 airports and the flights between them. The disease started in Mexico City.



They then reran the simulation to see how different strategies could reduce the spread. They found that shutting entire airports can obviously reduce infection.



But they also studied less obvious strategies such as looking for cities that play an important role in the network and reducing the flights between them by 25 per cent. This turned out to be a much more effective strategy.



They found that shutting entire airports only had a significant effect on spreading if it reduced travel by 95 per cent. By contrast, they could achieve the same effect by removing just 18 per cent of flights between cities ranked by a network measure called edge betweenness.



At best shutting entire airports could only cut infections by 18 per cent whereas removing specific flights reduced infections by up to 37 per cent.



"Selecting highly ranked single connections between cities for cancellation was more effective, resulting in fewer individuals infected with influenza, compared to shutting down whole airports," say Marcelino and Kaiser. This approach has the added benefit that it disrupts far fewer individuals



Because these guys used a model of the actual global network of airports and flights they were able to identify the specific connections that would need to be targeted. For an infection that starts in Mexico City, the highest ranked routes that would need to be targeted are Sao Paulo to Beijing, Sapporo to New York and Montevideo to Paris.



That seems an eminently sensible suggestion. However, policy makers might want to study this approach in more detail to check that the conclusions still hold if outbreaks occur in other places too.



Another idea worth checking is to see whether smaller airports could also play an important role in disease spreading. Marcelino and Kaiser study a network consisting of the top 500 airports but the world is blessed with some 4000 airports in total.



It's not inconceivable that some of these could play a crucial role in linking different parts of the world in a way that could facilitate disease spreading.



Ref: http://arxiv.org/abs/1205.3245
: Critical Paths In A Metapopulation Model Of H1N1: Efficiently Delaying Influenza Spreading Through Fight Cancellation

Proof-of-principle experiment shows how humanoid robots can co-operate on a large scale by copying the behavior of social insects and bacterial colonies.






In recent years, various companies and labs have developed impressive humanoid robots that walk, shuffle and even run. Some even dance in groups of up to 20, performing sophisticated choreographed routines.



This kind of synchronisation is no easy task. One way to do it is have one robot as the leader, broadcasting details of its movement and position over a network that the other robots all follow.



The trouble is that network dynamics are not as predictable as choreographers would like. Small delays of half a second or so are common while some messages can be delayed by several seconds. That's clearly not good enough for a dance routine or any other type of synchronised behaviour.



So the approach preferred by roboticists is to program each robot with the dance routine, synchronise their internal clocks at the start of the performance and then leave them to it.



The advantage is that If the performance is reasonably short, the chances of the clocks becoming desynchronised can be made small. The disadvantage is that if the robots become desynchronised--if one falls over, for example--there is no way to regain synchronisation.



So roboticists have been searching for a better form of synchronisation that is more robust to the various trials and tribulations that befall robotic dancers. Today, Patrick Bechon and Jean-Jacques Slotine at the Massachusetts Institute of Technology in Cambridge, reveal a new approach based on the biological phenomenon of quorum sensing.



Biologists have long puzzled over the ability of bacteria and social insects to sense not only the presence of compatriots but their number and to synchronise their behaviour.



It turns out that these creatures perform this synchronisation using a process called quorum sensing. This works by constantly releasing signalling molecules into the environment while at the same time measuring the local concentration of these molecules.



This concentration rises as more creatures join the local population and so is an effective measure of population density. When the concentration rises over some threshold level, it triggers a different behaviour such cell division, pathogen production and nest building.



Now Bechon and Slotine say a similar approach provides a robust way to synchronise humanoid robots. The ideal approach to synchronisation is for each robot to have access to every other robot's position. Instead, the quorum sensing approach gives, each robot access to a global variable such as the average position or average clock time. Each robot can also change this variable because it contributes to the average.



The idea is that if each robot attempts to synchronise with this global average, the swarm as whole should keep good time.



These guys test out their approach with a group of eight NAO robots built by the French robotics company Aldebaran. Each has an internal clock which attempts to synchronise with a global average time maintained by a central server.



It's important to point out that the server is not acting as a master with the robots as slaves that simply follow its signal. If the connection to the central is lost, the robots simply continue with routine but without centralised synchrony.



Instead, the central server is more like a a kind of environment that the robots can sense and interact with.



This arrangement has the significant advantage that if one robot falls over it can simply get back up and join in again when it has resynchronised its movements with the group (see video
).



This work is part of a broader development in robotics. The advent of relatively cheap humanoid robots from Aldebaran and other companies means that the large-scale sychronisation of humanoid swarms is now possible.



That's interesting because while synchrony allows large numbers of robots to do the same thing at the same time--such as dancing or marching--it also allows large number so robots to do different but related tasks at the same time.



In other words, synchrony is an enabling technology for large scale co-operation. And that opens the way to an entirely new set of tasks that robots could do--think manufacturing and construction. Perhaps even nest building.



Ref: arxiv.org/abs/1205.2952
: Synchronization And Quorum Sensing In A Swarm Of Humanoid Robots

Quantum tunneling had always been thought too complex to simulate on today's simple quantum computers. Now a new approach to quantum computing has changed that and opens the door to more complex simulations.






The exploitation of quantum weirdness for computing is one of the great goals of modern physics. It's promise is dramatic for a wide range of number-crunching tasks.



But quantum computers have another trick up their sleeves which is sometimes forgotten--the ability to simulate other quantum systems. Physicists have already shown how quantum computers of various types can simulate phenomenon such as quantum phase transitions and the dynamics of entanglement--things that classical computers simply cannot handle.



There is one quantum phenomenon, however, that has never been simulated--tunnelling. This is the ability of quantum particles to cross a barrier without seeming to have passed through it.



There's no reason in principle why quantum computers can't simulate tunnelling. The problem is the complexity of the task.



The simulations performed so far have all involved so-called analogue processes which are relatively straightforward. The idea here is that the mathematical description of one system, its Hamiltonian, is exactly reproduced in another system.



So watching one system tells you exactly how the other would behave. This is known as analogue quantum particle simulation and it works well provided you can find systems that match in required way. Watching quantum phase transitions is good example because many systems share the same mathematical description.



For more complex problems, physicists have recently been thinking about another approach. The idea here is to break the mathematical system into different parts and simulate them separately. This is known as digital quantum particle simulation and it has huge potential for events that involve more than one object, such as quantum chemistry and tunneling.



The problem is the sheer complexity of these calculations, which require numerous quantum logic gates processing dozens of qubits. That's always been beyond the state-of-the-art for quantum computing.



Earlier this year, however, Andrew Sornborger at the University of Georgia in Athens showed how the case of a single particle tunnelling through a barrier
could be made simple enough to simulate on today's quantum computers. Such a demonstration would be the first example of a digital quantum simulation.



And today Guan Ru Feng and pals at Tsinghua University in Beijing say they've done it. To simulate tunnelling, these guys used a quantum computer that relies on nuclear magnetic resonance to manipulate qubits in encoded in the carbon and hydrogen atoms that make up chloroform molecules. They say this is the first demonstration of a quantum tunnelling simulation using an NMR quantum computer.



That should open the floodgates for more digital quantum simulations in future. It's significant because this approach has the potential to simulate much more complex quantum phenomenon than is currently possible. Expect to see more of it.



Ref: arxiv.org/abs/1205.2421
: Experimental Digital Simulation of Quantum Tunneling in a NMR Quantum Simulator

Latest simulation shows that the magnetic nozzles required for antimatter propulsion could be vastly more efficient than previously thought--and built with today's technologies






Smash a lump of matter into antimatter and it will release a thousand times more energy than the same mass of fuel in a nuclear fission reactor and some 2 billion times more than burning the equivalent in hydrocarbons.



So it's no wonder that antimatter is the dream fuel for science fiction fans.



The problem, of course, is that antimatter is in rather short supply making the prospect of ever building a rocket based on this technology somewhat remote.



But from time to time physicists put aside these concerns and have a little fun working out how good antimatter rocket engines can be. Today it's the turn of Ronan Keane at Western Reserve Academy and Wei-Ming Zhang at Kent State University, both in Ohio, who take a new approach to the problem with some interesting results.



First, some basic rocket science. The maximum speed of a rocket depends on its exhaust velocity, the fraction of mass devoted to fuel and the configuration of the rocket stages. "The latter two factors depend strongly on fine details of engineering and construction, and when considering space propulsion for the distant future, it seems appropriate to defer the study of such specifics," say Keane and Zhang.



So these guys focus on the exhaust velocity--the speed of the particles produced in matter-antimatter annihilations as they leave the rocket engine.



The thrust from these annihilations comes largely from using a magnetic field to deflect charged particles created in the annihilation. These guys focus on the annihilation of protons and antiprotons to produce charged pions.



So an important factor is how efficiently the magnetic field can channel these particles out of the nozzle.



In fact, the exhaust velocity of these pions depends on two factors--their average initial velocity when they are created and the efficiency of the magnetic nozzle design.



In the past, various physicists have calculated that the pions should travel at over 90 per cent the speed of light but that the nozzle would be only 36 per cent efficient. That translates into an average exhaust velocity of only a third of lightspeed, barely relativistic and somewhat of a disappointment for antimatter propulsion fans.



All that is set to change now, however. Keane and Zhang have come up with a different set of figures with the help of software developed by CERN that simulates the interaction between particles, matter and fields of various kinds.



CERN uses this software, called GEANT4 (short for Geometry and Tracking 4), to better understand how particles behave at the Large Hadron Collider, which itself collides beams of protons and antiprotons. So it's ideally suited to Keane and Zhang's task.



The new work produces some good news and some bad news. First the bad. The new simulations indicate that pions produced in this way will be significantly slower than previously thought, travelling at only 80 per cent of light speed.



The good news is that the GEANT4 simulations indicate that a magnetic nozzle can be much more efficient than previously envisioned, reaching 85 per cent efficiency. That translates into an average exhaust velocity of about 70 per cent light speed. That's much more promising. "True relativistic speeds once more become a possibility," say Keane and Zhang.



These guys have another surprise up their sleeve. Their nozzle has a magnetic field strength of around 12 Tesla. "Such a field could be produced with today’s technology, whereas prior nozzle designs anticipated and required major advances in this area," they say.



That will bring a smile to the face of many science fiction fans.



There is, of course, the small problem of gathering enough antimatter for a journey of any decent length. The number of antiatoms made at CERN is small enough to be countable. By one estimate, at this rate it will take a thousand years to make a single microgram of antimatter.



Keane and Zhang point out that all earlier estimates predate the PAMELA spacecraft's discovery last year that Earth is surrounded by a ring of antiprotons
and suggest that this could mined for fuel. What they don't mention, however, is that PAMELA spotted only 28 antiprotons in two years--far less than the rate at which CERN makes them on a daily basis.



Keane and Zhang finish by noting that other fuel technologies have advanced at an exponential rate, liquid hydrogen production, for example. If antimatter manufacture turns out to follow a similar trajectory, who knows what could happen.



Interesting, entertaining and wildly ambitious--all good fun.



Ref: arxiv.org/abs/1205.2281
: Beamed Core Antimatter Propulsion: Engine Design and Optimisation

The best of the rest from the Physics arXiv this week



Three-Body Amplification Of Photon Heat Tunneling




Complexity and Information: Measuring Emergence, Self-organization, and Homeostasis at Multiple Scales




The Variability Of Tidewater-Glacier Calving: Origin Of Event-Size And Interval Distributions




Can Timeouts Change the Outcome of Basketball Games?




Parent-Offspring Conflict In Feral Dogs: A Bioassay




Is Eternal Inflation Past-Eternal? And What if It Is?

The ability to teleport photons through 100 kilometres of free space opens the way for satellite-based quantum communications, say researchers






Teleportation is the extraordinary ability to transfer objects from one location to another without travelling through the intervening space.



The idea is not that the physical object is teleported but the information that describes it. This can then be applied to a similar object in a new location which effectively takes on the new identity.



And it is by no means science fiction. Physicists have been teleporting photons since 1997 and the technique is now standard in optics laboratories all over the world.



The phenomenon that makes this possible is known as quantum entanglement, the deep and mysterious link that occurs when two quantum objects share the same existence and yet are separated in space.



Teleportation turns out to be extremely useful. Because teleported information does not travel through the intervening space, it cannot be secretly accessed by an eavesdropper.



For that reason, teleportation is the enabling technology behind quantum cryptography, a way of sending information with close-to-perfect secrecy.



Unfortunately, entangled photons are fragile objects. They cannot travel further than a kilometre or so down optical fibres because the photons end up interacting with the glass breaking the entanglement. That severely limits quantum cryptography's usefulness.



However, physicists have had more success teleporting photons through the atmosphere. In 2010, a Chinese team announced that it had teleported single photons over a distance of 16 kilometres. Handy but not exactly Earth-shattering.



Now the same team says it has smashed this record. Juan Yin at the University of Science and Technology of China in Shanghai, and a bunch of mates say they have teleported entangled photons over a distance of 97 kilometres across a lake in China.



That's an impressive feat for several reasons. The trick these guys have perfected is to find a way to use a 1.3 Watt laser and some fancy optics to beam the light and receive it.



Inevitably photons get lost and entanglement is destroyed in such a process. Imperfections in the optics and air turbulence account for some of these losses but the biggest problem is beam widening (they did the experiment at an altitude of about 4000 metres). Since the beam spreads out as it travels, many of the photons simply miss the target altogether.



So the most important advance these guys have made is to develop a steering mechanism using a guide laser that keeps the beam precisely on target. As a result, they were able to teleport more than 1100 photons in 4 hours over a distance of 97 kilometres.



That's interesting because it's the same channel attenuation that you'd have to cope with when beaming photons to a satellite with, say, 20 centimetre optics orbiting at about 500 kilometres. "The successful quantum teleportation over such channel losses in combination with our high-frequency and high-accuracy [aiming] technique show the feasibility of satellite-based ultra-long-distance quantum teleportation," say Juan and co.



So these guys clearly have their eye on the possibility of satellite-based quantum cryptography which would provide ultra secure communications around the world. That's in stark contrast to the few kilometres that are possible with commercial quantum cryptography gear.



Of course, data rates are likely to be slow and the rapidly emerging technology of quantum repeaters will extend the reach of ground-based quantum cryptography so that it could reach around the world, in principle at least.



But a perfect, satellite-based security system might be a useful piece of kit to have on the roof of an embassy or distributed among the armed forces.



Something for western security experts to think about.



Ref: arxiv.org/abs/1205.2024
: Teleporting Independent Qubits Through A 97 Km Free-Space Channel

Invisibility cloaks that work for microwaves are easy to make using simple building blocks. Now engineers have created the equivalent building blocks for visible light.






Given the headlines associated with invisibility cloaks, you could be forgiven for thinking that a Star Trek-style cloaking device will be available in stores before the holiday season. Sadly, no.



It's true that in recent years researchers have made great strides in their theoretical understanding of how these cloaks work and consequently built increasingly complex and impressive devices.



But these devices generally work in the microwave region of the electromagnetic spectrum, where wavelengths are measured in centimetres. A few teams have made devices that work in the optical realm but only in two dimensions and over extremely short distances.



The problem is simple. The building blocks of microwave cloaks are split ring resonators--c-shaped pieces of metal in which electric and magnetic fields resonate when they interact with a electromagnetic wave. This interaction is what steers microwaves in a way that cloaks objects



These split ring resonators need to be a little smaller than the wavelengths they are designed to interact with. For microwaves, that's the centimetre scale and so are relatively easy to make and assemble.



But that's much harder at optical wavelengths, where the scale is measured in nanometres..What's more, losses become much more significant on this scale because most metals tend to absorb visible light rather than transmit it.



Consequently, nobody has been able to make split ring resonators that work for visible light. The optical cloaks made so far all rely on other structures such as gold nanorods or holes drilled through silicon slabs.)



So anybody who finds a way to create the optical version of split ring resonators might reasonably be said to be sitting on an important breakthrough.



Enter Arseniy Kuznetsov at the Data Storage Institute in Singapore and a few pals. These guys say they've found an alternative to split ring resonators that work well at optical frequencies, with few losses.



This alternative is silicon nanospheres between 100 and 200 nm in diameter. It turns out that these spheres behave just like split ring resonators in the sense that they allow for the same kind of magnetic resonances when they interact with light.



The trouble of course is making these spheres. Chemists have been making much smaller spheres--between 2nm and 50nm in diameter--for some time now using various self assembly techniques to grow tiny crystals or 'quantum dots' as they are called. (These are useful because they fluoresce at well defined and controllable wavelengths.)



To make larger spheres, Kuznetsov blast a slab of silicon with a short pulse of high-powered laser light. This evaporates the silicon which then condenses into liquid balls. These solidify into spheres as they fall back on to the surface as a kind of silicon rain.



The end result is a surface covered with solid silicon nanospheres between 100 and 200nm in diameter.



Kuznetsov calculated how the magnetic fields inside these balls should resonate when they are zapped with light and then used a hi-tec tweezer and magnifying set to see whether the behaviour matched the theory.



Turns out it does. This magnetic resonance can be tuned to match any part of the visible spectrum simply selecting spheres of a specific size.



That's important because it opens up an entirely new way make invisibility cloaks that operate in the visible region. "These optical systems open up new perspectives for fabrication of low-loss optical metamaterials and nanophotonic devices," they say.



That could have a significant impact on the way optical cloaks are designed and made.



There are plenty of challenges ahead, however. Not least of these will be finding a reliable way to make nanospheres of a specific size.



Then there is the problem of assembling nanospheres into useful devices in a way that scales. That's not something that a tweezer and magnifying set can help with, no matter how hi-tec.



Having said that, there is huge interest and big money invested in cloaking research, which is one reason why progress has been so rapid in the last ten years. So it wouldn't be a total surprise if these problems were solved in double quick time.



Ref: arxiv.org/abs/1205.1610
: Magnetic light

Researchers have been able to store single images in a cloud of rubidium atoms for several years. Now they've gone a step further






One of the enabling technologies for a quantum internet is the ability to store and retrieve quantum information in a reliable and repeatable way.



One of the more promising ways to do this involves photons and tiny clouds of rubidium gas. Rubidium atoms have an interesting property in that a magnetic field causes their electronic energy levels to split, creating a multitude of new levels. Switching the field off, returns the atoms to their normal state.



So one way to store photons, and the quantum information they carry, is to send them into a cloud of rubidium atoms and switch on the magnetic field. If the photons have a wavelength that is absorbed by the new electronic levels in the gas, they become trapped within it.



As long as the field remains on, that is. Switch the field off and the atoms are forced to emit the photons allowing the information they hold to be retrieved.



That immediately suggests a way of building a quantum memory.



Indeed various teams have spent the last few years testing this technique and others related to it. The results have been impressive. They can store not just single photons but entire images which they send into the gas by placing an image mask over the beam.



The storage lasts for tens of microseconds and the images can be retrieved with accuracies approaching 90 per cent. (The storage duration is limited by the movement of the atoms in the gas which blurs the images over time.)



Today, Quentin Glorieux and pals at the National Institute of Standards and Technology in Maryland go a step further. These guys have used exactly this technique to store two images at the same time. That's clearly a very short movie but the important point is that it's a proof-of-principle demonstration of the technique.



The images are the letter T and the letter N and the sequence of pictures above shows the images being released from the gas, as recorded by a high speed camera in 100 nanosecond frames. "We have demonstrated that multiple images can be stored and retrieved at different times, allowing the storage of a short movie in an atomic memory," say Glorieux and co.



Interestingly, the images are released on a "last in, first out" basis, so this movie is running backwards.



That's an impressive feat. Until now, sequences of images have only ever been stored at the same time in solid state media, such as holographic memories.These seem to have impressive potential as quantum memory devices.



But it looks as if rubidium gas clouds will give holograms a run for their money in this race.



Ref: arxiv.org/abs/1205.1495
: Temporally Multiplexed Storage of Images in a Gradient Echo Memory

If quantum mechanics plays an important role is biology, we'll want to copy it. If it doesn't, we'll want to know why not






One of the biggest questions in biology is whether the processes of life are able to exploit quantum effects to improve their lot.



Nobody questions whether living things are ultimately quantum at some level--we're all made of quantum objects called atoms and glued together by quantum forces. If you look closely enough at any biological process, you'll see quantum mechanics at work.



The question is whether nature exploits quantum mechanics to achieve things that are not possible in the ordinary, classical world.



There is a growing debate on this topic. On the one hand, evidence has begun to mount that quantum mechanics may play a role in processes such as photosynthesis, bird navigation and the sense of smell. On the other, critics say this evidence is far from conclusive and may simply show that reality always appears quantum in nature, if you look closely enough.



Today, Neill Lambert at the Japanese research institute RIKEN in Saitama and a few pals, provide a much needed review of the evidence in this area, focusing in particular on photosynthesis and bird navigation.



These guys point out that the efforts to find evidence of quantum effects in photosynthesis are largely focused on the fact that energy somehow crosses large protein molecules with an efficiency close to 100 per cent. That's hard to explain classically.



The evidence for quantum effects in bird navigation is a little more speculative but leaves less room for a classical explanation. It is based on the idea that that a weak magnetic field can influence the outcome of a certain type of chemical reaction in bird retinas involving radical ion pairs.



The details make for interesting reading.



This is an area that has gained huge attention in recent years. The promise, of course, is that if nature has found ways to exploit quantum mechanics, then it should be possible for us to copy those techniques. Think artificial photosynthesis, robotic noses and navigation systems, perhaps even artificial life.



But the alternative is just as interesting. If nature has not found a way to exploit quantum mechanics, an equally important question is: why not? Is it merely an oversight on the part of evolution or is there some other deeper reason why evolution cannot exploit quantum mechanics?



Important questions. And for answers, a good place to start is with a comprehensive overview of the research.



Ref: arxiv.org/abs/1205.0883
: Functional Quantum Biology In Photosynthesis And Magnetoreception

Biochemists have long imagined that autocatalytic sets can explain the origin of life. Now a new mathematical approach to these sets has even broader implications






One of the most puzzling questions about the origin of life is how the rich chemical landscape that makes life possible came into existence.



This landscape would have consisted among other things of amino acids, proteins and complex RNA molecules. What's more, these molecules must have been part of a rich network of interrelated chemical reactions which generated them in a reliable way.



Clearly, all that must have happened before life itself emerged. But how?



One idea is that groups of molecules can form autocatalytic sets. These are self-sustaining chemical factories, in which the product of one reaction is the feedstock or catalyst for another. The result is a virtuous, self-contained cycle of chemical creation.



Today, Stuart Kauffman at the University of Vermont in Burlington and a couple of pals take a look at the broader mathematical properties of autocatalytic sets. In examining this bigger picture, they come to an astonishing conclusion that could have remarkable consequences for our understanding of complexity, evolution and the phenomenon of emergence.



They begin by deriving some general mathematical properties of autocatalytic sets, showing that such a set can be made up of many autocatalytic subsets of different types, some of which can overlap.



In other words, autocatalytic sets can have a rich complex structure of their own.



They go on to show how evolution can work on a single autocatalytic set, producing new subsets within it that are mutually dependent on each other. This process sets up an environment in which newer subsets can evolve.



"In other words, self-sustaining, functionally closed structures can arise at a higher level (an autocatalytic set of autocatalytic sets), i.e., true emergence," they say.



That's an interesting view of emergence and certainly seems a sensible approach to the problem of the origin of life. It's not hard to imagine groups of molecules operating together like this. And indeed, biochemists have recently discovered simple autocatalytic sets that behave in exactly this way.



But what makes the approach so powerful is that the mathematics does not depend on the nature of chemistry--it is substrate independent. So the building blocks in an autocatalytic set need not be molecules at all but any units that can manipulate other units in the required way.



These units can be complex entities in themselves. "Perhaps it is not too far-fetched to think, for example, of the collection of bacterial species in your gut (several hundreds of them) as one big autocatalytic set," say Kauffman and co.



And they go even further. They point out that the economy is essentially the process of transforming raw materials into products such as hammers and spades that themselves facilitate further transformation of raw materials and so on. "Perhaps we can also view the economy as an (emergent) autocatalytic set, exhibiting some sort of functional closure," they speculate.



Could it be that the same idea--the general theory of autocatalytic sets--can help explain the origin of life, the nature of emergence and provide a mathematical foundation for organisation in economics?



As Kauffman and friends say with just a little understatement: "We believe that these ideas are worth pursuing and developing further."



We'll look forward to following the work as it progresses.



Ref: arxiv.org/abs/1205.0584
: The Structure of Autocatalytic Sets: Evolvability, Enablement, and Emergence

The best of the rest from the Physics arXiv this week



A New Perspective On Dark Energy Modeling Via Genetic Algorithms




Astrophysics Independent Bounds On The Annual Modulation Of Dark Matter Signals




The Effects Of Environmental Disturbances On Tumor Growth




Graphene Battery Made Of Low Cost Reduced Graphene Oxide




No Fundamental Limitation on Studying Living Organisms and Other Complex Systems with Statistical Methods




Predicting Fixation Tendencies of the H3N2 Influenza Virus by Free Energy Calculation

The growing interest in a market for personal data that shares profits with the individuals who own the data could change the business landscape for companies like Facebook





Facebook's imminent IPO raises an interesting issue for many of its users. The company's value is based on its ability to exploit the online behaviours and interests of its users.


To justify its sky-high valuation, Facebook will have to increase its profit per user at rates that seem unlikely, even by the most generous predictions. Last year, we looked at just how unlikely this is
.



The issue that concerns many Facebook users is this. The company is set profit from selling user data but the users whose data is being traded do not get paid at all. That seems unfair.



Today, Bernardo Huberman and Christina Aperjis at HP Labs in Palo Alto, say there is an alternative. Why not pay individuals for their data? TR looked at this idea earlier this week
.



Setting up a market for private data won't be easy. Chief among the problems is that buyers will want unbiased samples--selections chosen at random from a certain subgroup of individuals. That's crucial for many kinds of statistical tests.



However, individuals will have different ideas about the value of their data. For example, one person might be willing to accept a few cents for their data while another might want several dollars.



If buyers choose only the cheapest data, the sample will be biased in favour of those who price their data cheaply. And if buyers pay everyone the highest price, they will be overpaying.



So how to get an unbiased sample without overpaying?



Huberman and Aperjis have an interesting straightforward solution. Their idea is that a middle man, such as Facebook or a healthcare provider, asks everyone in the database how much they want for their data. The middle man then chooses an unbiased sample and works out how much these individuals want in total, adding a service fee.



The buyer pays this price without knowing the breakdown of how much each individual will receive. The middle man then pays each individual what he or she asked, keeping the fee for the service provided.



The clever bit is in how the middle man structures the payment to individuals. The trick here is to give each individual a choice. Something like this:



Option A: With probability 0.2, a buyer will get access to your data and you will receive a payment of $10. Otherwise, you’ll receive no payment.
Option B: With probability 0.2, a buyer will get access to your data. You’ll receive a payment of $1 irrespectively of whether or not a buyer gets access




So each time a selection of data is sold, individuals can choose to receive the higher amount if their data is selected or the lower amount whether or not it is selected.



The choice that individuals make will depend on their attitude to risk, say Huberman and Aperjis. Risk averse individuals are more likely to choose the second option, they say, so there will always be a mix of people expecting high and low prices.



The result is that the buyer gets an unbiased sample but doesn't have to pay the highest price to all individuals.



That's an interesting model which solves some of the problems that other data markets suffer from.



But not all of them. One problem is that individuals will quickly realise how the market works and work together to demand ever increasing returns.



Another problem is that the idea fails if a significant fraction of individuals choose to opt out altogether because the samples will then be biased towards those willing to sell their data. Huberman and Aperjis say this can be prevent by offering a high enough base price. Perhaps.



Such a market has an obvious downside for companies like Facebook which exploit individual's private data for profit. If they have to share their profit with the owners of the data, there is less for themselves.



And since Facebook will struggle to achieve the kind of profits per user it needs to justify its valuation, there is clearly trouble afoot.



Of course, Facebook may decide on an obvious way out of this conundrum--to not pay individuals for their data.



But that creates an interesting gap in the market for a social network that does pay a fair share to its users (perhaps using a different model to Huberman and Aperjis').



Is it possible that such a company could take a significant fraction of the market? You betcha!



Either way, Facebook loses out--it's only a question of when.



This kind of thinking must eventually filter through to the people who intend to buy and sell Facebook shares.



For the moment, however, the thinking is dominated by the greater fool theory of economics--buyers knowingly overpay on the basis that some other fool will pay even more. And there's only one outcome in that game.



Ref: arxiv.org/abs/1205.0030
: A Market for Unbiased Private Data: Paying Individuals According to their Privacy Attitudes

Claims that Twitter can predict the outcome of elections are riddled with flaws, according to a new analysis of research in this area






It wasn't so long ago that researchers were queuing up to explain Twitter's extraordinary ability to predict the future.



Tweets, we were told, reflect the sentiments of the people who send them. So it stands to reason that they should hold important clues about the things people intend to do, like buying or selling shares, voting in elections and even about paying to see a movie.



Indeed various researchers reported that social media can reliably predict the stock market, the results of elections and even box office revenues



But in recent months the mood has begun to change. Just a few weeks ago, we discussed new evidence indicating that this kind of social media is not so good at predicting box office revenues
after all. Twitter's predictive crown is clearly slipping.



Today, Daniel Gayo-Avello, at the University of Oviedo in Spain, knocks the crown off altogether, at least as far as elections are concerned. His unequivocal conclusion: “No, you cannot predict elections with Twitter.”



Gayo-Avello backs up this statement by reviewing the work of researchers who claim to have seen Twitter's predictive power. These claims are riddled with flaws, he says.



For example, the work in this area assumes that all tweets are trustworthy and yet political statements are littered with rumours, propaganda and humour.

Neither does the research take demographics into account. Tweeters are overwhelmingly likely to be younger and this, of course, will bias any results. "Social media is not a representative and unbiased sample of the voting population," he says.



Then there is the problem of self selection. The people who make political remarks are those most interested in politics. The silent majority is a huge problem, says Gayo-Avello and more work needs to be done to understand this important group.



Most damning is the lack of a single actual prediction. Every analysis on elections so far has been done after the fact. "I have not found a single paper predicting a future result," says Gayo-Avello.



Clearly, Twitter is not all it has been cracked up to be when it comes to the art of prediction. Given the level of hype surrounding social media, it's not really surprising that the more sensational claims do not stand up to closer scrutiny. Perhaps we should have seen this coming (cough).



Gayo-Avello has a solution. He issues the following challenge to anybody working in this area: "There are elections virtually all the time, thus, if you are claiming you have a prediction method you should predict an election in the future!"



Ref: arxiv.org/abs/1204.6441
: “I Wanted to Predict Elections with Twitter and all I got was this Lousy Paper”: A Balanced Survey on Election Prediction using Twitter Data

A statistical analysis of a 3000-year old calendar reveals that astronomers in ancient Egypt must have known the period of the eclipsing binary Algol






The Ancient Egyptians were meticulous astronomers and recorded the passage of the heavens in extraordinary detail. The goal was to mark the passage of time and to understand the will of the Gods who kept the celestial machinery at work.



Egyptian astronomers used what they learnt to make predictions about the future. They drew these up in the form of calendars showing lucky and unlucky days.



The predictions were amazingly precise. Each day was divided into three or more segments, each of which was given a rating lying somewhere in the range from very favourable to highly adverse.



One of the best preserved of these papyrus documents is called the Cairo Calendar. Although the papyrus is badly damaged in places, scholars have been able to extract a complete list of ratings for days throughout an entire year somewhere around 1200 BC.



An interesting question is how the scribes arrived at their ratings. So various groups have studied the patterns that crop up in the predictions. Today, Lauri Jetsu and buddies at the University of Helsinki in Finland reveal the results of their detailed statistical analysis of the Cairo Calendar. Their conclusion is extraordinary.



These guys arranged the data as a time series and crunched it with various statistical tools designed to reveal cycles within it. They found two significant periodicities. The first is 29.6 days--that's almost exactly the length of a lunar month, which modern astronomers put at 29.53059 days.



The second cycle is 2.85 days and this is much harder to explain. However, Jetsu and co make a convincing argument that this corresponds to the variability of Algol, a star visible to the naked eye in the constellation of Perseus.



Algol is interesting because every 2.867 days, it dims visibly for a few hours and then brightens up. This was first discovered John Goodricke in 1783, who used naked eye observations to measure the variability.



Astronomers later explained this variability by assuming that Algol is a binary star system. It dims when the dimmer star passes in front of the brighter one.



Nothing else in the visible night sky comes close to having a similar period so it's reasonable to think that the 2.85 and the 2.867 day periods must refer to the same object. "Everything indicated that the two best periods in [the data] were the real periods of the Moon and Algol," say Jetsu and co.



And yet that analysis leaves a nasty taste in the mouth. The ancients were extremely careful observers. If Goodricke measured a period of 2.867 days (68.75 hours), the Egyptians ought to have been able to as well.



This is where the astronomy becomes a little more complex. The period of binary star systems ought to be easy to predict. But in recent years, astronomers have discovered that Algol's period is changing in ways that they do not yet fully understand.



One reason for this is that Algol turns out to be a triple system with a third star in a much larger orbit. And of course, the behaviour of triple systems is more complex. It is also hard to model based on real data since observations of Algol's variability go back only 300 years.



Or so everyone had thought. Jetsu and co now think that the difference between the ancient and modern measurements is no accident and that the period was indeed shorter in those days. So the Egyptian data can be used as an additional data point to better constrain and understand Algol's behaviour.



So not only did the ancients' discover the variable stars 3000 years before western astronomers, the data is good enough to help understand the behaviour of this complex system. A truly remarkable conclusion.



Ref: arxiv.org/abs/1204.6206
: Did The Ancient Egyptians Record The Period Of The Eclipsing Binary Algol – The Raging One?

In a significant step forward for all-optical computing, physicists build a silicon transistor that works with pure light






Electrons are pretty good at processing information but not so good at carrying it over long distances. Photons, on the other hand, do a grand job of shuttling data round the planet but are not so handy when it comes to processing it.



As a result, transistors are electronic and communication cables are optical. And the world is burdened with a significant amount of power hungry infrastructure for converting electronic information into the optical variety and vice versa.



So it's no surprise that there is significant interest in developing an optical transistor that could make the electronic variety obsolete.



There's a significant problem, however. While various groups have built optical switches, optical transistors must also have a number of other properties so that they can be connected in a way that can process information.



For example, their output must be capable of acting as the input for another transistor--not easy if the output is a different frequency from the input, for instance. What's more, the output must be capable of driving the input for at least two other transistors so that logic signals can propagate, a property known as fanout. This requires significant gain. On top of this, each transistor must preserve the quality of the logic signal so that errors do no propagate. And so on.



The trouble is that nobody has succeeded in making optical transistors that can do all and can also be made out of silicon.



Today, Leo Varghese at Purdue University in Indiana and a few pals say they've built a device that take a significant step in this direction.



Their optical transistor consists of a microring resonator next to an optical line. In ordinary circumstances the light supply enters the optical line, passes along it and then outputs. But at a specific resonant frequency, the light interacts with the microring resonator, vastly reducing the output. In this state, the output is essentially off even though the supply is on.



The trick these guys have perfected is to use another optical line, called the gate, to heat the microring, thereby changing its size, its resonant frequency and its ability to interact with the output.



That allows the gate to turn the output on and off.



There's an additional clever twist. The microring's interaction with the gate is stronger than with the supply-output line. That's significant because it means a small gate signal can control a much bigger output signal.



Varghese and co say the ratio of the gate signal to the supply is almost 6 dB. That's enough to power at least two other transistors, which is exactly the fan out property that optical transistors require.



These guys have even built a device out of silicon with a bandwidth capable of data rates of up to 10 GHz.



That's an impressive result, particularly the silicon compatibility.



Nevertheless, there are significant hurdles ahead before an all-optical computer made with these devices can hope to compete against its electronic cousins.



The biggest problem is power consumption. Much of the power consumption in electronic transistors comes from the need to charge the lines connecting them to the operating voltage.



In theory, optical transistors could be even more efficient--their lines don't need charging at all. But in practice, lasers burn energy as if it were twenty dollar bills. For that reason, it's not at all clear that optical transistors can match the efficiency of electronic chips.



And with the computer industry now responsible for almost 2 per cent of global carbon dioxide emissions, almost as much as aviation, power consumption may turn out to be the overarching factor for the future direction of information processing.



Ref: arxiv.org/abs/1204.5515
: A Silicon Optical Transistor

The best of the rest from the Physics arXiv this week



Using Quasars As Standard Clocks For Measuring Cosmological Redshift




A Cost- Effective Design of Reversible Programmable Logic Array




The Computational Complexity Of Minesweeper




Cortical Columns For Quick Brains




A Recent Bifurcation In Arctic Sea-Ice Cover

Heavyweight cosmologists are battling it out over whether the universe had a beginning. And despite appearances, they may actually agree

Researchers are using Google Adwords to test the persuasive power of different messages.






The Web has fundamentally changed the business of advertising in just a few years. So it stands to reason that the process of creating ads is bound to change too.



The persuasive power of a message is a crucial ingredient in any ad. But settling on the best combination of words is at best a black art and at worst, little more than guesswork.



So advertisers often try to test their ads before letting them out into the wild.



The traditional ways to test the effectiveness of an advertising campaign are with a survey or a focus group. Surveys are shown to a carefully selected group of people who are asked to give their opinion about various different forms of words. A focus group is similar but uses a small group of people in more intimate setting, often recorded and watched from behind a one way mirror.



There are clear disadvantages with both techniques. Subjects are difficult to recruit, hard to motivate (often requiring some kind of financial reward ) and the entire process is expensive and time consuming.



What's more, the results are hard to analyse since any number of extraneous effects can influence them. Focus groups, for example, are notoriously susceptible to group dynamics in which the view of one individual can come to dominate. And there is a general question over whether recruited subjects can ever really measure the persuasiveness of anything.



Then there is the obvious conflict created by the fact that a subject is not evaluating the messages under the conditions in which they were designed to work ie to get the attention of an otherwise disinterested reader.



So there's obvious interest in finding a better way to test the value of persuasive messages. One approach is to use crowdsourcing services such as Mechanical Turk to generate an immediate readership willing to take part.



But Turks are paid to take part. So the results are no better than those that conventional methods produce, although they are cheaper and quicker to collect.



Today, Marco Guerini at the Italian research organisation Trento-Rise and a couple of buddies say they've found an interesting way round this: to test messages on Google's AdWords service.



The idea here is to use Google Adwords to place many variations of a single message to see which generates the highest click through rate.



That's a significant improvement over previous methods. The subjects are not paid and make their choice in the very conditions in which the message is designed to work. And the data is quick and relatively cheap to collect.



Google already has a rudimentary tool that can help with this task. The so-called AdWords Campaign Experiments (ACE) tool allows users to test two variations of an ad side-by-side.



But to really get to the heart of persuasiveness requires a much more rigorous approach. Guerini and co make some small steps in this direction by testing various adverts for medieval art at their local castle in Trento.



These guys used Google's ACE tool to test various pairs of adverts and achieved remarkable success with some of their ads. One ad, for example, achieved a click through rate of over 6 per cent from just a few hundred impressions--that's an impressive statistic in an industry more used to measuring responses in fractions of a percent.



However, this click through rate was not different in a statistically significant way from its variant so there's no way of knowing what it was about the message that generated the interest.



So while Guerini and co's experiments are interesting pilots they are not extensive enough to provide any insight into the nature of persuasive messaging. That will need testing on a much larger scale.



These will not be easy experiments to perform and present numerous challenges. For example, the process of changing the wording of an advert is fraught with difficulty. Then there is the question of whether this method is able to test anything other adverts designed for AdWords. It might have limited utility for testing the messages in magazine adverts or billboard posters, for instance.



But the important point is that these kinds of experiments are possible at all. And it's not hard to imagine interesting scenarios for future research. For example, AdWords could be used as part of an evolutionary algorithm. This process might start with a 'population' of messages that are tested on Adwords. The best performers are then selected to 'reproduce' with various random changes to form a new generation of messages that are again tested. And so on.



Who knows what kind of insight these kinds of approaches might produce into the nature of persuasiveness and the human mind. But we appear to have a way to carry out these experiments for the first time.



Ref: arxiv.org/abs/1204.5369
: Ecological Evaluation of Persuasive Messages Using Google AdWords

The ability to automatically determine personality type could change the way social networks target services to users






One of the foundations of modern psychology is that human personality can be described in terms of five different forms of behavior. These are:



1. Agreeableness--being helpful, cooperative and sympathetic towards others
2. Conscientiousness--being disciplined, organized and achievement-oriented
3. Extraversion--having a higher degree of sociability, assertiveness and talkativeness
4. Neuroticism--the degree of emotional stability, impulse control and anxiety
5. Openness--having a strong intellectual curiosity and a preference for novelty and variety




Psychologists have spent much time and many years developing tests that can classify people according to these criteria.



Today, Shuotian Bai at the Graduate University of Chinese Academy of Sciences in Beijing and a couple of buddies say they have developed an online version of the test that can determine an individual's personality traits from their behavior on a social network such as Facebook or Renren, an increasingly popular Chinese competitor.



Their method is relatively simple. These guys asked just over 200 Chinese students with Renren accounts to complete online, a standard personality test called the Big Five Inventory, which was developed at the University of California, Berkeley during the 1990s.



At the same time, these guys analyzed the Renren pages of each student, recording their age and sex and various aspects of their online behavior such as the frequency of their blog posts as well as the emotional content of the posts such as whether angry, funny or surprised and so on.



Finally, they used various number crunching techniques to reveal correlations between the results of the personality tests and the online behavior.



It turns out, they say, that various online behaviors are a good indicator of personality type. For example, conscientious people are more likely to post asking for help such as a location or e-mail address; a sign of extroversion is an increased use of emoticons; the frequency of status updates correlates with openness; and a measure of neuroticism is the rate at which blog posts attract angry comments.



Based on these correlations, these guys say they can automatically predict personality type simply by looking at an individual's social network statistics.



That could be extremely useful for social networks. Shuotian and comapny point out that a network might use this to recommend specific services. They give the rather naive example of an outgoing user who may prefer international news and like to make friends with others.



Other scenarios are at least as likely. For example, such an approach might help to improve recommender systems in general. Perhaps people who share similar personality characteristics are more likely to share similar tastes in books, films or each other.



There is also the obvious prospect that social networks would use this data for commercial gain; to target specific adverts to users for example. And finally there is the worry that such a technique could be used to identify vulnerable individuals who might be most susceptible to nefarious persuasion.



Ethics aside, there are also certain questions marks over the result. One important caveat is how people's response to psychology studies online differs from those done at other times. That could clearly introduce some bias. Then there are the more general questions of how online and offline behaviours differs and how these tests vary across cultures. These are things that Shuotian and Co. want to study in the future.



In the meantime, it is becoming increasingly clear that the data associated with our online behavior is a rich and valuable source of information about our innermost natures.



Ref: arxiv.org/abs/1204.4809
: Big-Five Personality Prediction Based on User Behaviors at Social Network Sites

Cosmologists use the mathematical properties of eternity to show that although universe may last forever, it must have had a beginning











The Big Bang has become part of popular culture since the phrase was coined by the maverick physicist Fred Hoyle in the 1940s. That's hardly surprising for an event that represents the ultimate birth of everything.



However, Hoyle much preferred a different model of the cosmos: a steady state universe with no beginning or end, that stretches infinitely into the past and the future. That idea never really took off.



In recent years, however, cosmologists have begun to study a number of new ideas that have similar properties. Curiously, these ideas are not necessarily at odds with the notion of a Big Bang.



For instance, one idea is that the universe is cyclical with big bangs followed by big crunches followed by big bangs in an infinite cycle.



Another is the notion of eternal inflation in which different parts of the universe expand and contract at different rates. These regions can be thought of as different universes in a giant multiverse.



So although we seem to live in an inflating cosmos, other universes may be very different. And while our universe may look as if it has a beginning, the multiverse need not have a beginning.



Then there is the idea of an emergent universe which exists as a kind of seed for eternity and then suddenly expands.



So these modern cosmologies suggest that the observational evidence of an expanding universe is consistent with a cosmos with no beginning or end. That may be set to change.



Today, Audrey Mithani and Alexander Vilenkin at Tufts University in Massachusetts say that these models are mathematically incompatible with an eternal past. Indeed, their analysis suggests that these three models of the universe must have had a beginning too.



Their argument focuses on the mathematical properties of eternity--a universe with no beginning and no end. Such a universe must contain trajectories that stretch infinitely into the past.



However, Mithani and Vilenkin point to a proof dating from 2003 that these kind of past trajectories cannot be infinite if they are part of a universe that expands in a specific way.



They go on to show that cyclical universes and universes of eternal inflation both expand in this way. So they cannot be eternal in the past and must therefore have had a beginning. "Although inflation may be eternal in the future, it cannot be extended indefinitely to the past," they say.



They treat the emergent model of the universe differently, showing that although it may seem stable from a classical point of view, it is unstable from a quantum mechanical point of view. "A simple emergent universe model...cannot escape quantum collapse," they say.



The conclusion is inescapable. "None of these scenarios can actually be past-eternal," say Mithani and Vilenkin.



Since the observational evidence is that our universe is expanding, then it must also have been born in the past. A profound conclusion (albeit the same one that lead to the idea of the big bang in the first place).



Ref: arxiv.org/abs/1204.4658
: Did The Universe Have A Beginning?