Archive for February, 2008

Dark matter: we’ve been staring at it all along

Friday, February 29th, 2008

Dark nuggets

Astrobods have been searching for dark matter for a decade or so now. And despite it filling the known Universe, there’s been no sign of the stuff .

But could it be that we’ve been staring at it all along without knowing what we’ve been looking at?

That’s the claim of a couple of theorists in North America. They say that dark matter is in the form of large nuggets of dense quark matter or quark anti-matter and that this could explain a number of mysterious observations that astronomers have been making in recent years.

Michael Forbes of University of Washington, in Seattle and Ariel Zhitnitsky from the University of British Columbia in Vancouver say these nuggets float around in the form of tiny 10 ton lumps and would emit thermal radiation that should be straightforward to measure.

And sure enough, astronomers have been puzzling over a number of unexplained bands of radiation coming from the center of our galaxy that have been picked up by orbiting telescopes in recent years. The gamma ray observatory Integral has spotted a mysterious 511 KeV glow, the Compton gamma ray observatory has found an unexplained signal between 1- 20 MeV, the Chandra x-ray telescope sees a diffuse keV x-ray emission all over the place and WMAP has detected an excess of GHz microwave radiation from the inner core of the galaxy called the WMAP haze.

All this can be explained by quark nuggets, say the pair of astronomers. Interestingly, they also make a number of predictions about the nature and distrbution of the radiation emitted by nuggets that should be straightforward to test. So unlike most dark matter theories, this one will stand or fall relatively quickly.

The theory also explains why none of the detectors on Earth have spotted these nuggets–the nuggets are distributed too sparsely to have been seen yet.

But when one of these ten ton beauties does come floating by, we’re not likely to miss its impact.

Ref: arxiv.org/abs/0802.3830: WMAP Haze: Directly Observing Dark Matter?

First 3D image of a streamer

Thursday, February 28th, 2008

3d-streamer



Streamers are the whispy electronic filaments that feel their way towards the ground in the fraction of a second before a lightning strike. They differ from the main strike in that they do not significantly increase the gas temperature.

They are also seen in nature as sprites, giant electronic discharges that sit 100 kilometres or so above active thunderstorms.

A number of groups have captured ordinary 2D images of streamers, which have a complex, fragmented shape. But nobody has determined their 3D structure.

Now Sanders Nijdam and pals at Eindhoven University of Technology in the Netherlands have captured the first 3D image of a streamer.

Their set up is pretty straigthforward. A stereo camera photographing a discharge in air. They then digitised the images to create a model of the streamer.

That’s handy because streamers may be useful in various applications such as ozone generation, bio fuel processing and plasma assisted combustion, say the group.

Cool huh?

Ref: arxiv.org/abs/0802.3639: Stereo-photography of Point-Plane Streamers in Air

The vibration harvest

Wednesday, February 27th, 2008

Vibration harvester

All them turbines, drills and shakers in our modern factories make one almighty din.

We’re talking about a substantial amount of a-jumpin and a-jiggling which generally goes to waste. Couldn’t there be a way of harvesting this energy so that it can be re-used?

Turns out Tom Sterken and pals at IMEC, an independent nanostuff research lab in Belgium, have thought of a way to do it and have built a device that can do it.

It’s a MEMs gadget that consists of a tiny mass on a spring connected to a capacitor. As the mass bounces around, it generates a voltage which is stored by the capacitor.

When attached to an (unspecified) piece of industrial equipment, Sterken says his device generates 90 nanowatts of power. That doesn’t seem much: it’s not going to recharge your mobile phone or ipod.

But it might power the sensors needed to monitor this and other devices. And these harvesters can only get better.

Ref: arxiv.org/abs/0802.3060: Characterisation of an Electronic Vibration Harvester

How plankton blooms are born

Tuesday, February 26th, 2008

Plankton bloom

Massive plankton blooms are the plague of the oceans. They starve local species by exhausting an ocean of its food and oxygen, they turn vast areas of sea to the colour of milk and have a profound effect on the ocean food web.

But where do they come from? Nobody knows. At least they didn’t until Mathias Sandulescu and buddies from Carl-von-Ossietzky Universitat in Oldenburg Germany, started hunting for the origin. And they reckon they’ve found it.

Plankton blooms, it turns out, are born in the wake vortices that form downstream of islands. But there’s a caveat: the blooms only form in certain circumstances.

Sandulescu says that the essential extra factor is an upwelling of nutrient rich waters upstream of the islands and has tested the idea using mathematical models of the ocean currents around the Canary Islands off the coast of Africa.

The model shows how nutrients become trapped in the downstream vortices and provide a steady source food on which the plankton feast as they bloom. When the bloom gets large enough, it escapes from the vortex and heads out into open water.

Of course, this is a perfectly normal process. Most blooms never get to the size of small countries and never wipe out entire ecosystems of ocean life.But now we know where they come from, it may be possible to monitor their production and the way in which they grow after their birth.

Ref: arxiv.org/abs/0802.3532: Biological Activity in the Wake of an Island Close to a Coastal Upwelling

The physics of human body weight changes

Monday, February 25th, 2008

Body Mass

If you put on a few pounds over the holiday season, this may interest you.
Weight changes are the result of an imbalance between the energy you derive from the food you’ve eaten and the energy you’ve been expending to maintain life and perform physical work. At first glance, you’d think this would be a pretty easy relationship to quanitfy.

Not so. If the question is how does an imbalance affect the the distribution of fat and lean tissues within your body, the answer turns out to be surprisingly hard to get a handle on.

Tha thasn’t stopped Carson Chow and Kevin Hall at the Laboratory of Biological Modeling in Bethesda, Maryland, from having a go. They’ve have created a mathematical model that describes what is going on when this energy balance changes.

They say there are essentially two answers to the problem.

In the first case, the composition of fat and lean tissue within your body and its overall mass are uniquely determined. So whatever you do, your body heads to a uniquely determined mass.

In the second case, the body composition can vary over an infinite number of states. So for example, when your overall mass increases, the amount of lean tissue may go up while the amount of fat goes down. Or the other way around is. Or the amount of both types of tissue may increase. So your body could respond to a particular change in eating habits in an infinite number of ways.

Curiously, it’s hard to distinguish between these two cases by simply changing diet and monitoring body weight. Chow and Hall say there simply isn’t enough evidence to determine whether the human body operates in the first regime or the second.

But they think they know how they can find out. The trick, they say, will be to create diets that change either the amount of lean tissue or the amount of fat tissue but not both. And then see what happens. In this way, you can hold one of the variables steady to see how the mechanism works. Just what this diet might be, they don’t say.

The whole area is of more than academic interest because it could have a direct bearing on the efficacy of treatments such as lioposuction and the way in which serious eating disorders are handled. Not to mention us ordinary snackers who want to control our weights more effectively.

So you might want to hang fire if you are hoping to get the holiday love handles removed surgically.

Ref: arxiv.org/abs/0802.3234: The Dynamics of Human Body Weight Change

In case ya missed ‘em…

Sunday, February 24th, 2008

This week’s pearls from the physics arXiv blog:

Saving Earth from the Sun’s expansion

Read it and beep

The quantum graphity question

They came from Mercury…

Ball’s ‘n’ fire

Saturday, February 23rd, 2008

The best of the rest from the arXiv this week:

Plasma Treatment Advantages for Textiles

Electron Mass Shift in Nonthermal Systems

How Efficient is Towing a Cargo by a Micro-swimmer?

Movie Recommendation Systems Using An Artificial Immune System

They came from Mercury…

Thursday, February 21st, 2008

Mercurian meteorite

Astrobods have found several dozen meteorites from Mars and the Moon that have made their way to Earth over the years. These rocks were launched during major impacts there.

It’s unlikely that we’ll ever see a meteorite from Venus arrive on Earth: the Venusian atmosphere is just too thick. But what of Mercury?

According to Brett Gladman from the University of British Columbia in Vancouver, Mercurian meteorites may be an order of magnitude more common on Earth than we thought.

He and a pal say Mercury is the only planet where impact speeds are routinely 5 to 20 times greater than the escape speed.

So they calculated the percentage of rock likely to escape from Mercury towards Earth after an impact. It turns out that up to 5% of rocks leaving Mercury with speeds greater than 9 km per second could reach Earth within 30 million years.

So Mercurian meteorites probably arrive here at about half the rate of rocks from Mars.

That means that somewhere on Earth, in somebody’s meteorite collection there lies a little bit of Mercury. Get looking!

Ref: arxiv.org/abs/0801.4038: Mercurian Impact Ejecta: Meteorites and Mantle

The quantum graphity question

Wednesday, February 20th, 2008

Emergent gravity

Physicists have been searching for a quantum theory of gravity some time. Most believe that the new theory will require some kind of modification to general relativity or quantum theory.

One of the ideas in vogue at the moment is that general relativity is actually an emergent phenomenon from some deeper physics.

Now Tomasz Konopka from Utrecht University in the Netherlands and others are developing an idea called quantum graphity that could prove it.

The thinking is that on a fundamental level the universe is like a dynamic graph with vertices and nodes. At high energies, this graph is highly connected and symmetric. But at low energies, it condenses into a system that has properties such as a geometry, thermodynamics and locality (the property that distant objects cannot influence each other).

That sounds suspiciously like the universe we live in, which is manna to theoretical physicists.

Could this so-called “quantum graphity” be the deeper physics from which general relativity emerges?

Who knows but a few physicists think it’s worth exploring further. The idea raises various interesting questions. What is the nature of the temperature at which the condensation occurs? Is it a real physical temperature or something else? How exactly do the familiar properties of geometry and gravity behave in this model?

And, most important of all, what evidence might we look for to confirm the idea that a condensation took place earlier in the history of the cosmos? If these guys can make some kind of testable prediction, then quantum graphity will alreayd be one giant step ahead of every other attempt to create a quantum theory of gravity.

Ref: arxiv.org/abs/0801.0861: Quantum Graphity: a Model of Eemergent Locality

Read it and beep

Tuesday, February 19th, 2008

Reading text is a simple enough task for humans. But unless it’s cleaned up and served on a plate computers just can’t do it.

At least they couldn’t until Mireille Boutin and pals from Purdue University took a shot at the problem.

These guys have built an impressive algorithm that looks for and finds text in real-life cluttered images.

And it works well. In their, albeit limited, tests on  65 real-life images, the algorithm correctly identified the text 97 per cent of the time.

Cars that can read signposts, anyone?

Ref: arxiv.org/abs/0801.4807: Automatic Text Area Segmentation in Natural Images