Posts Tagged ‘University of Oxford’

Only for the truly obsessed: a movie featuring gold nanocrystal vibrations

Thursday, May 23rd, 2013

Folks at the London Centre for Nanotechnology (at the University College of London) have released a film made with a pioneering 3D imaging technique that shows how gold nanocrystals vibrate. From the May 23, 2013 news release on EurekAlert,

A billon-frames-per-second film has captured the vibrations of gold nanocrystals in stunning detail for the first time.

The film, which was made using 3D imaging pioneered at the London Centre for Nanotechnology (LCN) at UCL [University College of London], reveals important information about the composition of gold. The findings are published in the journal Science.

Jesse Clark, from the LCN and lead author of the paper said: “Just as the sound quality of a musical instrument can provide great detail about its construction, so too can the vibrations seen in materials provide important information about their composition and functions.”

“It is absolutely amazing that we are able to capture snapshots of these nanoscale motions and create movies of these processes. This information is crucial to understanding the response of materials after perturbation. “

Caption: The acoustic phonons can be visualized on the surface as regions of contraction (blue) and expansion (red). Also shown are two-dimensional images comparing the experimental results with theory and molecular dynamics simulation. The scale bar is 100 nanometers. Credit: Jesse Clark/UCL

Caption: The acoustic phonons can be visualized on the surface as regions of contraction (blue) and expansion (red). Also shown are two-dimensional images comparing the experimental results with theory and molecular dynamics simulation. The scale bar is 100 nanometers. Credit: Jesse Clark/UCL

Here are more details from the news release,

Scientists found that the vibrations were unusual because they start off at exactly the same moment everywhere inside the crystal. It was previously expected that the effects of the excitation would travel across the gold nanocrystal at the speed of sound, but they were found to be much faster, i.e., supersonic.

The new images support theoretical models for light interaction with metals, where energy is first transferred to electrons, which are able to short-circuit the much slower motion of the atoms.

The team carried out the experiments at the SLAC National Accelerator Laboratory using a revolutionary X-ray laser called the “Linac Coherent Light Source”. The pulses of X-rays are extremely short (measured in femtoseconds, or quadrillionths of a second), meaning they are able to freeze all motion of the atoms in any sample, leaving only the electrons still moving.

However, the X-ray pulses are intense enough that the team was able to take single snapshots of the vibrations of the gold nanocrystals they were examining. The vibration was started with a short pulse of infrared light.

The real keeners can watch the movie if they click on the link to the May 23, 2013 news release on EurekAlert.

The team developing this movie was international in scope (from the news release),

The research team included contributors from UCL, University of Oxford, SLAC, Argonne National Laboratory [US] and LaTrobe University, Australia.

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Are we and our world a computer simulation?

Tuesday, December 11th, 2012

There is a fascinating Dec. 10, 2012 news item on Nanowerk about a philosophical question that’s being researched by a team of physicists at the University of Washington (Note: I have removed a link),

The concept that current humanity could possibly be living in a computer simulation comes from a 2003 paper published in Philosophical Quarterly (“Are You Living In a Computer Simulation?“) by Nick Bostrom, a philosophy professor at the University of Oxford. In the paper, he argued that at least one of three possibilities is true:

The human species is likely to go extinct before reaching a “posthuman” stage.

Any posthuman civilization is very unlikely to run a significant number of simulations of its evolutionary history.

We are almost certainly living in a computer simulation.

He also held that “the belief that there is a significant chance that we will one day become posthumans who run ancestor simulations is false, unless we are currently living in a simulation.”

Here’s what the University of Washington physicists, from the Dec. 10, 2012 University of Washington news release by Vincent Stricherz, which originated the news item,

With current limitations and trends in computing, it will be decades before researchers will be able to run even primitive simulations of the universe. But the UW team has suggested tests that can be performed now, or in the near future, that are sensitive to constraints imposed on future simulations by limited resources.

Currently, supercomputers using a technique called lattice quantum chromodynamics and starting from the fundamental physical laws that govern the universe can simulate only a very small portion of the universe, on the scale of one 100-trillionth of a meter, a little larger than the nucleus of an atom, said Martin Savage, a UW physics professor.

…

However, Savage said, there are signatures of resource constraints in present-day simulations that are likely to exist as well in simulations in the distant future, including the imprint of an underlying lattice if one is used to model the space-time continuum.

The supercomputers performing lattice quantum chromodynamics calculations essentially divide space-time into a four-dimensional grid. That allows researchers to examine what is called the strong force, one of the four fundamental forces of nature and the one that binds subatomic particles called quarks and gluons together into neutrons and protons at the core of atoms.

“If you make the simulations big enough, something like our universe should emerge,” Savage said. Then it would be a matter of looking for a “signature” in our universe that has an analog in the current small-scale simulations.

Savage and colleagues Silas Beane of the University of New Hampshire, who collaborated while at the UW’s Institute for Nuclear Theory, and Zohreh Davoudi, a UW physics graduate student, suggest that the signature could show up as a limitation in the energy of cosmic rays.

In a paper they have posted on arXiv, an online archive for preprints of scientific papers in a number of fields, including physics, they say that the highest-energy cosmic rays would not travel along the edges of the lattice in the model but would travel diagonally, and they would not interact equally in all directions as they otherwise would be expected to do.

“This is the first testable signature of such an idea,” Savage said.

If such a concept turned out to be reality, it would raise other possibilities as well. For example, Davoudi suggests that if our universe is a simulation, then those running it could be running other simulations as well, essentially creating other universes parallel to our own.

“Then the question is, ‘Can you communicate with those other universes if they are running on the same platform?’” she said. [emphasis mine]

Here’s the citation for and a link to the arXiv.org paper by Beane, Davoudi, and Savage,

Constraints on the Universe as a Numerical Simulation by Silas R. Beane, Zohreh Davoudi, Martin J. Savage (Submitted on 4 Oct 2012 (v1), last revised 9 Nov 2012 (this version, v2))

Fascinating, yes?

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Rail system and choreography metaphors in a couple of science articles

Wednesday, January 25th, 2012

If you are going to use a metaphor/analogy when you’re writing about a science topic  because you want to reach beyond an audience that’s expert on the topic you’re covering or you want to grab attention from an audience that’s inundated with material, or you want to play (for writers, this can be a form of play [for this writer, anyway]), I think you need to remain true to your metaphor. I realize that’s a lot tougher than it sounds.

I’ve got examples of the use of metaphors/analogies in two recent pieces of science writing.

First, here’s the title for a Jan. 23, 2012 article by Samantha Chan for The Asian Scientist,

Scientists Build DNA Rail System For Nanomotors, Complete With Tracks & Switches

Then, there’s the text where the analogy/metaphor of a railway system with tracks and switchers is developed further and abandoned for origami tiles,

Expanding on previous work with engines traveling on straight tracks, a team of researchers at Kyoto University and the University of Oxford have used DNA building blocks to construct a motor capable of navigating a programmable network of tracks with multiple switches.

…

In this latest effort, the scientists built a network of tracks and switches atop DNA origami tiles, which made it possible for motor molecules to travel along these rail systems.

Sometimes, the material at hand is the issue. ‘DNA origami tiles’ is a term in this field so Chan can’t change it to ‘DNA origami ties’ which would fit with the railway analogy. By the way, the analogy itself comes from (or was influenced by) the title the scientists chose for their published paper in Nature Nanotechnology (it’s behind a paywall),

A DNA-based molecular motor that can navigate a network of tracks

All in all, this was a skillful attempt to get the most out of a metaphor/analogy.

For my second example, I’m using a Jan. 12, 2012 news release by John Sullivan for Princeton University which was published in Jan. 12, 2012 news item on Nanowerk. Here’s the headline from Princeton,

Ten-second dance of electrons is step toward exotic new computers

This sets up the text for the first few paragraphs (found in both the Princeton news release and the Nanowerk news item),

In the basement of Hoyt Laboratory at Princeton University, Alexei Tyryshkin clicked a computer mouse and sent a burst of microwaves washing across a silicon crystal suspended in a frozen cylinder of stainless steel.

The waves pulsed like distant music across the crystal and deep within its heart, billions of electrons started spinning to their beat.

Reaching into the silicon crystal and choreographing the dance of 100 billion infinitesimal particles is an impressive achievement on its own, but it is also a stride toward developing the technology for powerful machines known as quantum computers.

Sullivan has written some very appealing text for an audience who may or may not know about quantum computers.

Somebody on Nanowerk changed the headline to this,

Choreographing dance of electrons offers promise in pursuit of quantum computers

Here, the title has been skilfully reworded for an audience that knows more quantum computers while retaining the metaphor. Nicely done.

Sullivan’s text goes on to provide a fine explanation of an issue in quantum computing, maintaining coherence, for an audience not expert in quantum computing. The one niggle I do have is a shift in the metaphor,

To understand why it is so hard, imagine circus performers spinning plates on the top of sticks. Now imagine a strong wind blasting across the performance space, upending the plates and sending them crashing to the ground. In the subatomic realm, that wind is magnetism, and much of the effort in the experiment goes to minimizing its effect. By using a magnetically calm material like silicon-28, the researchers are able to keep the electrons spinning together for much longer.

Wasn’t there a way to stay with dance? You could have had dancers spinning props or perhaps the dancers themselves being blown off course and avoided the circus performers. Yes, the circus is more colourful and appealing but, in this instance, I would have worked to maintain the metaphor first introduced, assuming I’d noticed that I’d switched metaphors.

So, I think I can safely say that using metaphors is tougher than it looks.

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Entangling diamonds

Tuesday, December 6th, 2011

Usually when you hear about entanglement, they’re talking about quantum particles or kittens. On Dec. 2, 2011, Science magazine published a paper by scientists who had entangled diamonds (that can be touched and held in human hands). From the Dec. 1, 2011 CBC (Canadian Broadcasting Corporation) news article by Emily Chung,

Quantum physics is known for bizarre phenomena that are very different from the behaviour we are familiar with through our interaction with objects on the human scale, which follow the laws of classical physics. For example, quantum “entanglement” connects two objects so that no matter how far away they are from one another, each object is affected by what happens to the other.

Now, scientists from the U.K., Canada and Singapore have managed to demonstrate entanglement in ordinary diamonds under conditions found in any ordinary room or laboratory.

Philip Ball in his Dec. 1, 2011 article for Nature magazine describes precisely what entanglement means when applied to the diamond crystals that were entangled,

A pair of diamond crystals has been linked by quantum entanglement. This means that a vibration in the crystals could not be meaningfully assigned to one or other of them: both crystals were simultaneously vibrating and not vibrating.

Quantum entanglement — interdependence of quantum states between particles not in physical contact — has been well established between quantum particles such as atoms at ultra-cold temperatures. But like most quantum effects, it doesn’t tend to survive either at room temperature or in objects large enough to see with the naked eye.

Entanglement, until now, has been demonstrated at very small scales due to an issue with coherence and under extreme conditions. Entangled objects are coherent with each other but other objects such as atoms can cause the entangled objects to lose their coherence and their entangled state. In order to entangle the diamonds, the scientists had to find a way of dealing with the loss of coherence as the objects are scaled up and they were able to achieve this at room temperature. From the Emily Chung article,

Walmsley [Ian Walmsley, professor of experimental physics at the University of Oxford] said it’s easier to maintain coherence in smaller objects because they can be isolated practically from disturbances. Things are trickier in larger systems that contain lots of interacting, moving parts.

Two things helped the researchers get around this in their experiment, Sussman [Ben Sussman, a quantum physicist at the National Research Council of Canada and adjunct professor at the University of Ottawa] said:

  • The hardness of the diamonds meant it was more resistant to disturbances that could destroy the coherence.
  • The extreme speed of the experiment — the researchers used laser pulses just 60 femtoseconds long, about 6/100,000ths of a nanosecond (a nanosecond is a billionth of a second) — meant there was no time for disturbances to destroy the quantum effects.

Laser pulses were used to put the two diamonds into a state where they were entangled with one another through a shared vibration known as a phonon. By measuring particles of light called photons subsequently scattered from the diamonds, the researchers confirmed that the states of the two diamonds were linked with each other — evidence that they were entangled.

If you are interested in the team’s research and can get past Science magazine’s paywall, here’s the citation,

“Entangling Macroscopic Diamonds at Room Temperature,” by K.C. Lee; M.R. Sprague; J. Nunn; N.K. Langford; X.-M. Jin; T. Champion; P. Michelberger; K.F. Reim; D. England; D. Jaksch; I.A. Walmsley at University of Oxford in Oxford, UK; B.J. Sussman at National Research Council of Canada in Ottawa, ON, Canada; X.-M. Jin; D. Jaksch at National University of Singapore in Singapore. Science 2 December 2011: Vol. 334 no. 6060 pp. 1253-1256 DOI: 10.1126/science.1211914

All of the media reports I’ve seen to date focus on the UK and Canadian researchers and I cannot find anything about the contribution of the researcher based in Singapore.

I do wish I could read more languages as I’d be more likely to find information about work which is not necessarily going to be covered in English language media.

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