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Saturday, August 02, 2008
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Here’s an interesting chain of thought…
Imagine a black hole sucking in protons and electrons. With their higher mass, protons are likely to be preferentially sucked, giving the black hole a positive charge. (That’s not so unusual in space: a similar mechanism can give planets a charge because electrons escape their gravity more easily.)
But black holes also create such strong electrostatic fields at the horizon that positrons and electrons simply appear out of the vacuum.
In those circumstances, it’ll look as if the protons being sucked into the black hole are being converted into positrons.
So these kinds of black holes will look and behave like antimatter factories, say Cosimo Bambi from Wayne State University in Detroit and pals.
How might we we spot these exotic objects? Bambi and friends say a sure signature would be an excess of positrons in cosmic rays with an energy between 1 and 100 MeV coming from a black hole.
Anybody seen any of these?
Ref: arxiv.org/abs/0806.3440: Black Holes as Antimatter Factories
X-ray crystallography has been a workhorse technique for chemists since the 1940s and 50s. For many years, it was the only way to determine the 3D structure of complex biological molecules such haemoglobin, DNA and insulin. Many a Nobel prize has been won poring over diffraction images with a magnifying glass.
But x-ray crystallography has a severe limitation: it only works with molecules that form into crystals and that turns out to be a tiny fraction of the proteins that make up living things.
So for many years scientists have searched in vain for a technique that can image single molecules in 3D with the resolution, utility and cost-effectiveness of x-ray diffraction.
That search might now be over. Today, John Miao at the University of California, Los Angeles, makes the claim that he and his team have taken the first picture of a single unstained virus using a technique called x-ray diffraction microscopy. Until now this kind of imaging has only been done with micrometre-sized objects.
Miao’s improvement comes from taking a diffraction pattern of the virus and then subtracting the diffraction pattern of its surroundings. The resolution of his images is a mere 22 nanometres, that’s an improvement of three orders of magnitude.
If confirmed, that’s an extraordinary breakthrough. With brighter x-ray sources, the team says higher resolution images will be possible and that it’s just a matter of time before they start teasing apart the 3D structures of the many proteins that have eluded biologists to date.
But best of all, x-ray diffraction gear is so cheap that this kind of technique should be within reach of almost any university lab in the world.
Ref: arxiv.org/abs/0806.2875: Quantitative Imaging of Single, Unstained Viruses with Coherent X-rays
“It does, however, seem difficult to believe that our species, that has dominated the planet for a relatively short period of time, could have such a huge impact on our planet’s climate, whilst the Sun, the most massive body in the solar system whose influence dominates our planet, could have such little impact.”
So concludes Jeremy Dunning-Davies at the University of Hull in the UK in a paper discussing the various possible causes of climate change, including the influence of the Sun.
Dunning-Davies also says that a climate of fear has descended over the global warming issue that makes it hard to debate the science behind it in a reasonable way.
That’s a sorry state of affairs. Partly because the alternative hypothesis must alway be given the oxygen of open discussion. But not least because it means we’re going to miss something important when somebody, somewhere is afraid to speak up at the right time.
Some Comments on the Possible Causes of Climate Change
You could be forgiven for thinking that a quantum version of the internet is a couple of-afternoons-in-the-lab away from being plumbed into your living room. In reality, there are significant engineering challenges to overcome, says Jeff Kimble from the California Institute of Technology in Pasadena and one of the leading thinkers on the links between the quantum and information sciences.
If you want to know about some of the bigger hurdles that physicists face in wanting to build a quantum internet, you could do worse than look at his account of this field on the arXiv today.
Some of the challenges are particularly daunting such as the unambiguous creation and verification of entanglement.
But, ever the optimist, he concludes:
“I have every confidence that extending entanglement across quantum networks will create wonderful scientific opportunities for the exploration of physical systems that have not heretofore existed in the natural world”.
Ref: arxiv.org/abs/0806.4195: The Quantum Internet
The French start up Aldebaran-Robotics based in Paris has high hopes for its humanoid robot called NAO. The device is 57 cm high and weighs 4.5 kilograms (about the size of a 6 month old baby) and you may be about to see a lot more of it. The company has sent a simplified version to 16 teams playing in the Robocup humanoid football league this year.
NAO looks an impressive device, judging by the design, which the company has posted on the arXiv today. And others clearly agree. Earlier this year, the company picked up Euros 5 million in venture capital funding to help commercialise the device. The target market is university research labs involved in developing the next generation of software and hardware for robotics.
That’s a smart move because it could make NAO a de facto standard.
NAO doesn’t come cheap, however. A single robot will set you back Euros 10K but that is significantly cheaper than most other humanoids. Fujitsu’s HOAP costs $50K, for instance, and Honda hasn’t been able to put price on Asimo.
The company hopes that economies of scale will bring down the price as production scales up. Eventually it hopes to sell NAO to the public for Euros 4K each.
Better start saving.
Ref: arxiv.org/abs/0807.3223: The NAO Humanoid: A Combination of Performance and Affordability
Here’s a neat idea for a concert that’s going to blow a few minds if it ever takes to the stage.
A combination of three or more notes played together is called a chord. We know that certain musical chords sound happy while others sound sad (although nobody knows why). The mood of a piece of music then depends on the combination of chords being played. More than a few weighty tomes have been written about the way one chord can be transformed into another and the effect this has on the mood of the music.
But Kaca Bradonjic, a physicist at Boston University, says that musicians appear to have ignored one of the fundamental ways of changing the pitch of a note: the Doppler shift. He points out that it ought to be possible for an observer moving at a specific velocity to hear a sad sounding note as a happy one and vice versa.
Which means that the mood of a piece of music depends on the relative velocities of the audience and performers.
He calculates for example that to hear a C major chord as a C minor, the listener would need to be travelling at about 43 miles per hour, directly away from the source. That’s a fair speed. And the accelerations necessary to vary this effect from one note to another during a concert would make this one helluva roller coaster ride.
Talking of which, a (very quiet) roller coaster might be the perfect venue for the first concert of this type.
Ref: arxiv.org/abs/0807.2493: Relativity of musical mood
Liquid mirror telescopes are amazing contraptions. They start life as a puddle of mercury in a bowl. Set the whole thing spinning and the mercury spreads out in a thin film up the sides of the bowl.
The result is a fabulously cheap mirror that can be used for a variety of astronomical surveys. If we ever put a telescope on the moon, many astronomers have suggested that it should be one of this type.
It won’t have escaped your attention that liquid mirrors have important limitations. First, they can only point straight up. One or two people have played with fluids that have a higher viscosity than mercury and so can be tilted a few degrees this way or that but with limited success. And second, they cannot be made adaptive to correct for blurring introduced by the Earth’s atmosphere.
But that may change thanks to some interesting work being done by Denis Brousseau at Université Laval in Quebec et amis. Their machine controls the shape of the surface of a liquid mirror using a magnetic field. Mercury cannot be used, however, because it is too dense and changing its shape requires impractically powerful fields.
Instead the team have used a suspension of ferromagnetic nanoparticles in oil. A thin highly reflectivity layer of silver particles can then be spread across the surface of the ferrofluid to create a mirror.
Brousseau and co use an array of tiny coils behind the liquid to create a field that deforms the fluid surface as required. Their tests show this can be done fast and furiously enough to cope with the usual array of optical aberrations that the atmosphere throws up.
However, it may also be possible to use this technique to tilt liquid mirrors further than ever before. Ferrofluids can easily be made much more viscous than mercury and so combat the deforming pull of gravity. But they can also be deformed in a way that opposes gravity during each rotation of the supporting bowl. That could make them much more tiltable than mercury mirrors.
Of course, such a mirror would be mechanically more complex than the spinning bowls we have today and correspondingly more expensive. And sending one to the moon seems an unnecessary extravagance given the absence of an atmosphere there.
But here on Earth they could be made much more useful. It’s a combination of new-found utility and value for money that many astronomy projects on a budget will find irresistible.
Ref: arxiv.org/abs/0807.2397: Wavefront Correction with a Ferrofluid Deformable Mirror: Experimental Results and Recent Developments