Archive for February, 2008

Saving Earth from the Sun’s expansion

Monday, February 18th, 2008

Sun’s expansion

About 7 billion years from now the Sun will have swelled into a red giant with a radius larger than Earth’s orbit. We’re doomed. Or so we thought.

A ray of hope has been thrown our way by astronomers who say that as the Sun expands it will lose a significant portion of its mass (perhaps almost a third) in the form of a solar wind that is blown away. And as the mass drops, the radius of Earth’s orbit should increase.

That complicates things so Robert Connon Smith from the University of Sussex and a pal took on the task of determining whether this new thinking means Earth will survive or not.

And the answer is…cue drum roll.. that the planet will still be engulfed.

But they offer another ray of hope. Earth’s angular momentum around the smaller Sun need only be increased by 8 per cent to avoid engulfment and that, says Smith, could be achieved by engineering a series of asteroid swingbys that gradually lift us into a wider orbit.

If we start planning now, there’s hope for Mother Earth yet.

Ref: arxiv.org/abs/0801.4031: Distant Future of the Sun and Earth Revisited

In case ya missed ‘em…

Sunday, February 17th, 2008

This week’s gems from the physics arXiv blog:

Quantum computers and the death of chemistry

Inflatable mountains

The world’s first quantum ratchet

Who’s that on the runway?


Grids ‘n’ graphs

Saturday, February 16th, 2008

The best of the rest from the arXiv this week:

Stopping Supersonic Beams with an Atomic Coilgun

Artificial Immune Systems (AIS) – A New Paradigm for Heuristic Decision Making

Geometrically controllable electric fields

Extinction of an Infectious Disease: a Large Fluctuation in a Non-equilibrium System

Efficiency of Molecular Motors at Maximum Power

Who’s that on the runway?

Thursday, February 14th, 2008

Super dense landings

As an air traffic controller, the last thing you want is the catastrophic failure of your technology infrastructure.

And thankfully  it doesn’t usually happen like that. More often, there is a gradual degradation as one part of the system or another collapses.  Perhaps the communications die, the radar falls over or the computers crash, or maybe some of the ground structure becomes unavailable as airports have to close.

Obviously, air traffic controllers are trained to deal with these situations but could the air traffic itself be made more robust. Maxime Gariel and Eric Feron, from the Georgia Institute of technology in Atlanta, argue that it could and have even come up with a way of evaluating it.

They’ve studied various types of high-density, highly structured aircraft traffic and worked out how difficult it becomes to handle as information about it begins to fail. It turns out, they say, that certain types of traffic structure are easier to handle than others as the infrastructure degrades.

So if you’re at all worried about the introduction of Free Flight (where aircraft essentially manage their own traffic control in most areas), you needn’t be.   Gariel and Feron say it ain’t any worse than the current system should the air traffic control system go tits up.

Ref:  arxiv.org/abs/0801.4750: Graceful Degradation of Air Traffic Operations

The world’s first quantum ratchet

Wednesday, February 13th, 2008

Quantum ratchet

A quantum ratchet sounds like a handy device. The idea is to push a quantum particle in a specific direction by periodically kicking it with an unbiased force. But why would an unbiased force push it in a specific direction? It sounds as if you’re more likely to end up with a random walk/brownian-type motion.

The trick is to set up some kind of asymmetry in the system so that the particle “wants” to go in a particular direction. That’s how macroscopic ratchets work.

Now Itzhack Dana from Bar-Ilan University in Israel and some pals have set up the first quantum ratchet with a Bose Einstein Condensate (BEC).

They started with a symmetric pulsed optical standing wave. This periodically nudges the BEC, which has a momentum distribution that is symmetric when the particle is stationary.

Now this system looks symmetric because both the standing wave and the momentum are symmetric. The asymmetry arises when these two systems have different centers of symmetry. The BEC then migrates along the line between them.

Neat, huh! And a world first, according to the team (although that claim requires a coupla extra caveats).

Ref: arxiv.org/abs/0706.0871: Experimental Realization of Quantum-Resonance Ratchets at Arbitrary Quasimomenta

Inflatable mountains

Tuesday, February 12th, 2008

Artificial mountains

It’s best to ignore the crazier ideas on the physics arXiv. But every now and again something comes out of left field that is just too extraordinary to pass on.

Today, it’s a cheap way of changing the entire climate over relatively small regions of the Earth. Alexander Bolonkin (unaffiliated) suggests that inflatable mountains could do the trick. I’ll let Bolonkin take up the tale:

The mountains are inflatable semi-cylindrical constructions from thin film (gas bags) having heights of up to 3 – 5 km. They are located perpendicular to the main wind direction. Encountering these artificial mountains, humid air (wind) rises to crest altitude, is cooled and produces rain (or rain clouds).

“Many natural mountains are sources of rivers, and other forms of water and power production – and artificial mountains may provide these services for entire nations in the future. The film of these gasbags is supported at altitude by small additional atmospheric overpressure and may be connected to the ground by thin cables.

“This is a realistic and cheap method of economical irrigation, getting energy and virtual weather control on Earth at the current time.”

It couldn’t possibly go wrong.

Ref: arxiv.org/abs/0801.4212: Cheap Artificial AB-Mountains, Extraction of Water and Energy from Atmosphere and Change of Regional Climate

Quantum computers and the death of chemistry

Monday, February 11th, 2008

Quantum chemistry

When it comes to chemistry, computer simulations suck. The best they can do is simulate the electron dynamics of a helium atom, which is almost as simple as it gets. Never mind the rest of the periodic table and how the elements interact with each other.

But that’s gonna change when we get quantum computers, says Ivan Kassal, a chemist at Harvard University. He and a few buddies have worked out that a relatively simple quantum computer could generate an “exact, polynomial-time simulation of chemical reactions”.

It might not be long before we see the fruits of this kinda computation. Kassal calculates that a quantum computer with only 100 qubits could simulate the entire quantum dynamics of a lithium atom, a feat that is beyond all the conventional computer power on the planet right now.That’s impressive and destined to make chemistry even more unpopular than it already is. Who’ll want to mess around with test tubes and bunsen burners when a quantum computer can work out the answer while ya put ya feet up?

So how long before the quantum death of chemistry? That’s hard to say. Physicists are already messing around with quantum comuters that work with 10 quibits, not nearly enough to do anything interesting with yet. So we’ll need an order of magnitude improvement.

Sticking my neck out, I’d say we’ll have 100 quibit quantum computers within 7 years, based on nonlinear optical technology (gulp).

Ref: arxiv.org/abs/0801.2986: Quantum Algorithms for the Simulation of Chemical Dynamics

In case ya missed ‘em…

Sunday, February 10th, 2008

This week’s gems from the physics arXiv blog:

How cricketers get their eye in

First light from Keck’s null mode

Danger Theory and artificial immune systems

Model successfully predicts brain structure


Bats ‘n’ balls

Saturday, February 9th, 2008

The best of the rest from the arXiv this week:

Global Disease Spread: Statistics and Estimation of Arrival Times

Predictability and Epidemic Pathways in Global Outbreaks of Infectious Diseases: the SARS Case Study

A Comparison of Natural (English) and Artificial (Esperanto) Languages. A Multifractal Method based Analysis

Determination of the Newtonian Gravitational Constant Using Atom Interferometry

A Calendar Quipu of the Early 17th Century and its Relationship with the Inca Astronomy

Model successfully predicts brain structure

Thursday, February 7th, 2008

Pinwheels

The neuronal circuits in the part of your brain called the cerebral cortex are amongst the most complex structures in nature. Nobody knows how they form but it seems likely that self organisation plays a critical role.

Researchers have studied various models of self organisation that might explain how these circuits form but have come up against a problme. None of the models make experimentally testable predictions so ther is no way of choosing between them. Until now.

Matthias Kaschube at the Max Planck Institute for Dynamics and Self-Organization in Germany and a few pals have developed a model of self organisation within the brain that makes a specific prediction about a type of feature in the visual cortex called a pinwheel. These are topological defects in the arrangement of neurons that can easily be spotted in the brain.

Nobody is quite sure how pinwheels form but Kaschube says that in his model they form natrually if thenetwork allows for lang range interactiosn between neurons (which is what appears ot happen int eh visual cortex).

Their prediction is this: that the average density of pinwheels within the brain should be equal to pi, 3.141….

That’s pretty specific. They say there is not enough data to confirm their prediction but that a prelimanru study indicates that the value is somewhere close to 3, which is promising.

This is the first experimentally testable prediction ever made about brain structure, sys the group.
It looks like good work but I’d wanna know about the uniqueness of this solution. Can they show that no other model predicts a pinwheel density equal to pi?

Ref: arxiv.org/abs/0801.3651: Self-Organization and the Selection of Pinwheel Density in Visual Cortical Development