Archive for the ‘Mean machines’ Category

The fundamental patterns of traffic flow

Monday, March 9th, 2009


Take up the study of earthquakes, volcanoes or stock markets and the goal, whether voiced or not, is to find a way to predict future “events” in your field. In that sense, these guys have something in common with scientists who study traffic jams.

The difference is that traffic experts might one day reach their goal. The complexity of traffic flow, while  awe inspiring, may well be fundamentally different  to the complexity of stock markets and earthquake events.

At least that’s how Dirk Helbing at the Institute for Transport & Economics at the Technical University of Dresden in Germany, and his buddies see it.

Helbing says that one long standing dream of traffic experts is to identify the fundamental patterns of traffic congestion from which all other flows can be derived,  a kind of periodic table of traffic flows.

Now he thinks he has found it: a set of fundamental patterns of traffic flow that when identified on a particular road, can be used to create a phase diagram of future traffic states.

The phase diagrams can then be used to make forecasts about the way in which the flow might evolve.

That’ll be handy. But only if it’s then possible to do something to prevent the congestion. And that may be the trickiest problem of all.

Ref: Theoretical vs. Empirical Classification and Prediction of Congested Traffic States

Centimetre scale models could compute Casimir forces

Thursday, March 5th, 2009


The Casimir force is notoriously difficult to measure. So tricky is it, that the first accurate measurements weren’t made until 1997 and even today only a handful of labs around the world of capable of taking its measure.

Of course there are various ways of modelling what goes on theoretically but even the most powerful simulations these struggle to cope with simple shapes let alone complex geometries. Consequently, our knowledge of the Casimir  force and how to exploit it is poor.

Now John Joannopoulos and pals at MIT are suggesting a rather entertaining third way: to calculate Casimir forces using scale models that work like analogue computers.

What the team has noticed is a mathematical analogy between the Casimir force acting on microscopic bodies in a vacuum and the electromagnetic behaviour of macroscopic bodies floating in a conducting fluid.

So imagine you want to know what Casimir forces will act on a particular geometry. The idea is to build a centimetre scale metal model of this set up and place it in a conducting liquid such as saline. Then bombard it with microwaves and see what happens.

The result should give an accurate representation of the Casimir forces that would act on the microscopic scale.

The group explains:

Such a centimeter-scale model is not a Casimir “simulator,” in that one is not measuring forces, but rather a quantity that is mathematical related to the micron-scale Casimir force. In this sense, it is a kind of analog computer.

There’s no reason why those kinds of tests can’t be done now.  And that should give researchers a way of testing machines designed to reliably exploit the Casimir force for the first time.

Ref: Ingredients of a Casimir Analog Computer

Were gravitational waves first detected in 1987?

Wednesday, March 4th, 2009


In 1987, Joe Weber, a physicist  at the University of  Maryland, claimed to have detected gravitational waves at exactly the same moment that other astronomers witnessed the famous supernova of that year, SN1987A.

His equipment consisted of several massive aluminium bars that were designed to vibrate in a unique way when a large enough gravitational wave passed by.

His claims were ignored largely because other physicists calculated that gravitational waves ought to be several orders of magnitude too weak to be picked up by this kind of gear. (And he’d made several similar claims throughout the 60s and 70s that others had failed to repeat.)

But Weber’s claims may have to be re-examined, says Asghar Qadir, a physicist at  the National University of Sciences and Technology in Rawalpindi, Pakistan. He points out that predicting the strength of a gravitational wave is by no means easy and until recently, only first order effects have been considered.

He and colleagues have now worked out that in certain circumstances, second order effects can enhance the  waves. But this only happens when there is a certain kind of assymetry in the event that created the waves.

But get this: the assymetry can enhance the waves by a factor of 10^4.

He also  points out that SN1987A is aspherical in exactly the way that might create this enhancement. So if SN1987A generated gravitational waves, Weber would have been perfectly able to detect them.

Qadir concludes: “The claim of Weber to have observed gravitational waves from [SN1987A] needs to be re-assessed”.

By all accounts, Weber was a careful experimenter who got something of a rough deal for his efforts (the most comprehensive telling of the tale is in a book called Gravity’s Shadow by Harry Collins) .

Weber died in 2000 but it wouldn’t do any harm to re-examine his work in the light of this development.

Ref: Gravitational Wave Sources May Be “Closer” Than We Think

Liquid film motors finally explained

Thursday, February 26th, 2009


Last year, a group of Iranian physicists made the extraordinary discovery that motors can be made of nothing more than a thin film of water sitting in a cell bathed in two perpendicular electric fields. The unexpected result of this set up is that the water begins to rotate. Divide the water into smaller cells and each rotates too.

The team at the Sharif University of Technology in Tehran have a number of  fascinating videos of it in action. They raise an interesting question: the electric fields are static, so what’s making the water move?

Now Vlad Vladimirov at York University in the UK and a couple of droogs from Russia have delved into the hydrodynamics to work out what’s putting the oomph in this motor. The key turns out to be the scale on which the effect takes place.

They say the flow is generated at the edge of the cell where the electric field crosses the  (dielectric) boundary between the water and the cell container. The change in field sets the water flowing along the boundary.  Crucially, this flow is opposite on the other side of the cell and this is what sets up the circular flow.

Vladimirov and co point out that this effect can only happen in a thin film where effects such as viscosity and friction play a large role in the dynamics. In larger bodies of water, these effects become insignificant and the rotation stops. Which is why these motors have only ever been seen in thin films.

That has important implications becaue it shows the scale dependency of important phenomena. In fact, liquid film motors may turn out to be a game-changers for anybody involved in microfluidics.

Ref: Rotating Electrohydrodynamic Flow in a Suspended Liquid Film

The coming of age of hadrontherapy

Tuesday, February 24th, 2009


There’s a problem with conventional radiotherapy for tumours: the body absorbs the radiation as it passes through. So zap a deep seated tumour with X-rays and the dose decreases exponentially with the depth of target. This means that both diseased and healthy tissue end up getting targeted.

In 1946, Robert Wilson, a physicist  at FermiLab near Chicago pointed out that protons with an energy of between 200 and 250 MeV and carbon ions with an energy of 3500 to 4500 MeV work in a different way. Inside the body, they tend to dump all their energy at the end of their range. Not only that, but because the particles are charged, they can be sharply focused. He said that makes these particles ideal for targeting tumours.

It’s taken 60 years, but there is now real interest in hadrontherapy. Several thousand patients have been treated at various particle physics labs around the world. and therein lies the problem: the only places that can produce protons or carbon ions with these energies are  specialised accelerators such as those at GSI in Germany and Chiba in Japan.

There is one facility dedicated to medical work at the Loma Linda University Medical Centre near Los Angeles but it has become clear to the medical and physics community that more are desperately needed.

So how do you build reliable, easy-t0-use, affordable particle accelerators for medical centres? Enter Ugo Amaldi and buddies from the TERA Foundation in Italy, who today propose a design that they think could revolutionise this kind of treatment. (Amaldi was a hot shot at the European particle physics lab CERN for many years before turning to medical therapy.)

The idea is to build a cyclotron (a circular accelerator) and bolt it to a linac (a linear accelerator) and to call the hybrid a Cyclinac. So protons or carbon ions are injected into the cyclotron which stores and accelerates them. They are then injected into a linac which accelerates them to the appropriate energies for medical applications. The result is a therapeutic beam ready for action.

This design can also produce synchrotron  x-rays for other  medical apps.
Of course, there several significant engineering challenges ahead, like increasing the repetition rate of these devices to practical levels, something that Cyclinacs are being designed to address.

The big question, of course, is not whether such a project will be funded (everyone seems to agree on that) but when. And then where to build it. Given the Terra Foundation’s location, what odds on Italy being host to the first of these devices in Europe?

Ref: Cyclinacs: Fast-Cycling Accelerators for Hadrontherapy

Ptarithmetic: reinventing logic for the computer age

Friday, February 20th, 2009


In the last few years, a small group of logicians have attempted the ambitious task of re-inventing the discipline of formal logic.

In the past, logic has been thought of as the formal theory of “truth”.  Truth plays an important role in our society and as suchm a formal theory is entirely laudable and worthy. But it is not always entirely useful.

The new approach is to reinvent logic as the formal theory of computability. The goal is  to provide a systematic answer to the question “what is computable”. For obvious reasons,  so-called computability logic may turn out to be much more useful.

To understand the potential of this idea , just think for a moment about the most famous of logical systems called Peano Arithmetic, better known to you and me as “arithmetic”.

The idea is for computability logic to do for computation what Peano Arithmetic does for natural numbers.

The role of numbers is played by solvable computations and the collection of basic operations that can be performed on these computations forms the logical vocabulary of the theory.

But there’s a problem. There can be a big difference between something that is computable and something that is efficiently computable, says Giorgi Japaridze, a logician at Villanova University in Pennsylvania and the inventor of computability logic.

So he is proposing a modification (and why not, it’s his idea)–the system should allow only those computations that can be solved in polynomial time. He calls this polynomial time arithmetic or ptarithmetic for short.

The promise is that Japaridze’s system of logic will prove as useful to computer scientists as arithmetic is for everybody else.

What isn’t clear is whether the logical vocabulary of ptarithemtic is well enough understood to construct a system of logic around and beyond that, whether ptarithemtic makes a well-formed system of logic at all.

Those are big potential holes which Japaridze  may need some help to fill–even he would have to admit that he’s been ploughing a lonely furrow on this one since he put forward the idea in 2003.

But the potential pay offs are huge which make this one of those high risk , high potential pay off projects that just might be worth pursuing.

Any volunteers?

Ref: Ptarithmetic

What should robots do for us?

Monday, February 16th, 2009


Robots have great potential for assisting the old and disabled (not to mention the rest of  us) .  But if you’re developing one of these devices, where do you start? What kind of assistance you should concentrate on providing?

Young Sang Choi and buddies from the Healthcare Robotics Lab at Georgia Institute of Technology have worked it out for us. They asked a group of people suffering from amyotrophic lateral sclerosis (Stephen Hawking’s condition) what they most wanted a robot to be able to fetch for them.

Here are the top five requests (out of 43)…

  1. TV remote
  2. medicine pills
  3. prescription bottle
  4. glasses
  5. cordless phone

Seems sensible to compile a list like this. Other notable entries:  14 cellphone, 21 keys, 36 wallet, 38 drinking can (drink not specified)

Does such a list exist for able-bodied  people? And if not, what should be on it?

Ref: A List of Household Objects for Robotic Retrieval Prioritized by People with ALS

How to build a desktop Foucalt’s Pendulum

Friday, February 13th, 2009


Foucalt’s pendulum–a 28 kilogram bob suspended on a 67 metre wire– famously hangs in the Pantheon in Paris where Leon Foucalt himself demonstrated it in 1851.

The pendulum oscillates in a vertical plane which slowly rotates. The rotation is explained by the Earth’s motion which spins beneath the pendulum.

The length of the wire is important because it helps to iron out any irregularities that can always occur in the swing of a pendulum. In particular, it’s hard to set a pendulum in motion without imparting some ellipsoidal motion. The problem is that this ellipse always precesses, a motion that inevitably swamps the rotation caused by the Earth’s spin.

This is much less of a problem for long pendulums because the properties of the ellipsoidal motion are inversely related to the length of the wire.

If you have access to a 67 metre ceiling, you’re fine. But try it with a shorter pendulum and you’ll just never see the effect you want. That’s why Focault’s Pendulums are rather rare devices.

That may change thanks to some interesting work by Reinhard Schumacher and Brandon Tarbet at Carnegie Mellon University in Pittsburgh. What they’ve done is to work out how to drive a much shorter pendulum without allowing its ellipsoidal motion to precess.

They’ve done this with a motor that uses Faraday induction and magnetic repulsion to push a pendulum in a controlled fashion. The system is cleverly designed to cancel out any tendency to precess, whatever the size of the ellipse that the pendulum is describing.

But while the precession is suppressed, the rotation due to the Earth’s motion is not.

They’ve tested their idea on a 3 metre pendulum and say it works well.  They end their paper saying: “We plan to further test this method on even shorter pendula, since there is no lower limit at which the model given here should apply.”

Anybody want a desktop Focault Pendulum?

Ref: A Short Foucault Pendulum Free of Ellipsoidal Precession

Space Station simulator given emotions

Tuesday, February 3rd, 2009


Astronauts training to work on the International Space Station have to have mastered a mind-boggling amount of kit before they leave Earth. One of these devices is the Canadarm 2, a robotic arm used to manipulate experiments outside the station.

On Earth, astronauts train on a Canadarm 2 simulator connected to a virtual assistant that can spot potential errors, such as a move likely to smash the arm into the station. The assistant then offers hints and tips to the astronaut to help him or her make a correction or even issue a command to prevent damage.

The bad news for astronauts is that André Mayers and colleagues at Université de Sherbrooke in Canada who created the virtual assistant, have given it an unusual upgrade. In an attempt to help the simulator learn more about the astronauts who are using it, the team has programmed the assistant to experience the equivalent of an emotion when it records a memory of what has happened.

The problem is that the assistant receives a huge amount of data from each training session. It’s emotional response allows it to determine which of this data is most important, just as humans do. “This allows the agent to improve its behavior by remembering previously selected behaviors which are influenced by its emotional mechanism,” say the team.

The system is called the Conscious Tutoring System or CTS. It’s not clear from the paper how well the system works but how long before one unlucky astronaut hears the phrase: “I’m sorry Dave, I can’t do that.”

Ref: How Emotional Mechanism Helps Episodic Learning in a Cognitive Agent

Massive miscalculation makes LHC safety assurances invalid

Wednesday, January 28th, 2009


It just gets worse for CERN and its attempts to reassure us that the Large Hadron Collider won’t make mincemeat of the planet.

It’s beginning to look as if a massive miscalculation in the safety reckonings means that CERN scientists cannot offer any assurances about the work they’re doing.

In a truly frightening study, Toby Ord and pals at the University of Oxford say that “while the arguments for the safety of the LHC are commendable for their thoroughness, they are not infallible.”

When physicists give a risk assessment, their figure is only correct if their argument is valid. So an important questions is then: what are the chances that the reasoning is flawed?