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Stamping your mark on science

One of 10 Royal Mail stamps celebrating 350 years of the Royal Society

By Michael Banks

Physicist Ernest Rutherford – famous for his model of the atom in 1911 — once said that “All science is either physics or stamp collecting.”

But for all you stamp-collecting physicists out there you can now get your hands on 10 stamps launched today by the Royal Mail to celebrate 350 years of the Royal Society.

Featuring luminaries such as Isaac Newton, Benjamin Franklin and Robert Boyle, the first-class stamps are apparently the first to contain a “split-stamp” design (could it be a reference to Rutherford’s “splitting the atom” experiments in 1917?) — the portraits of the 10 fellows are each paired with a colourful image representing their achievements.

Royal Mail selected the 10 pioneering scientists with the help of the Royal Society and you can get your hands on the stamps by visiting any Post Office in the UK or online at www.royalmail.com/stamps

Crystal control moves towards 3D displays

In a step towards futuristic 3D-display screens, researchers in Singapore have found a simple way to control the growth of tiny crystals that have useful optical properties. By careful doping with lanthanide elements, the researchers found that they could adjust the crystal structure, size and emission spectra of sodium yttrium flouride (NaYF₄).

Known as “upconversion nanocrystals”, NaYF₄ crystals could play a critical role in the development of 3D-display technology, as they absorb near-infrared light and emit visible light. One promising application is dispersing them in transparent silicone displays, where infrared lasers can be used to generate images in 3D by scanning the silicone with invisible light causing the appropriate nanocrystals to emit visible light.

In addition, because NaYF₄ is nontoxic and biocompatible, there is great potential for advanced bioimaging or luminescent biological labelling. Using near-infrared radiation for these applications is safer and more accurate than using ultraviolet light.

But to be effective at upconversion, the crystals need to be less than 20 nm in size and have a hexagonal crystal structure. Achieving this has proven challenging, because small NaYF₄ crystals naturally favour the cubic crystal structure. Conversion to the hexagonal form typically requires harsh chemical reagents or prolonged heat treatments – conditions that can lead to other problems, such as the crystals sticking together or changing in size.

Doping decision

Now, Xiaogang Liu and colleagues at the National University of Singapore have found a much simpler way to control the growth of these crystals: by introducing carefully controlled quantities of lanthanide ions into the structure. Adding small amounts of heavy elements in this way is usually referred to as “doping” and is commonly used to make hybrid materials with unusual or desirable properties.

“We have discovered a new nanocrystal growth phenomenon induced by lanthanide doping,” Liu told physicsworld.com. ‘This allows us to control which phase the crystals grow in, but also adjust other properties. We can control the size of the nanocrystals – from several hundred nanometres to ten nanometres – but also fine tune the colour of their emissions from green to white and blue.’

The team first discovered that adding small amounts of gadolinium during crystal formation encouraged the crystals to form in the desired hexagonal phase. This takes place as some gadolinium ions take the place of yttrium ions, producing crystals of NaGdF₄ mixed in with NaYF₄. The presence of these crystals is thought to direct the rest to form in the hexagonal phase.

Lanthanide hunt

The team then explored other lanthanides, identifying that samarium and neodymium doping produced smaller crystals, while erbium, ytterbium and thulium doping changed the colour of the visible light that was emitted. Liu hopes that, with further research, optimized combinations can be found that will lead to other nanocrystals with different desirable properties.

This research is very interesting and can potentially open up new ideas in controlling nanomaterial growth Song Jin, University of Wisconsin

“This is a new concept in materials science, and a fundamental discovery rather than simply a synthesis technology – although it is a more efficient way to make small nanocrystals than conventional methods,” Liu says. “We will continue to explore the technological applications of these nanocrystals in photodynamic therapy, bioimaging, and animated 3D colour displays.”

Song Jin, a nanocrystals expert at the University of Wisconsin in Madison first heard about the work during a visit to Singapore in January. “This research is very interesting and can potentially open up new ideas in controlling nanomaterial growth. What intrigues me personally the most is that how the addition of dopants changes so much of the crystalline phase and morphology of the nanostructures.”

The study is described in Nature 463 1061.

Making sculptures that move

Why did you choose to study physics?

My interest in science started very early, probably with science-fiction books like the Tom Swift series, which are aimed at children. After brief stints in chemistry and engineering, I chose to study physics at Boston University because I found it the most challenging. I also had dreams of being an “inventor” and thought physics would give me an understanding of how things worked.

How did you become interested in sculpture?

Towards the end of my degree, I started spending time at the Rhode Island School of Design, where my future (and present!) wife Marji was studying sculpture and art education. The world of art was new to me, and I was particularly fascinated by some static wooden machine sculptures she had constructed. I kept suggesting that she make them move but she was not interested and suggested I try instead. After I graduated in 1974, I started working as a computer programmer for an insurance company. It was a tedious job that involved long periods of waiting, so during those downtimes I started sketching ideas for small kinetic toys. I left the programming job after nine months and started Wood That Works by selling these toys at local craft fairs. The toy designs evolved into the first kinetic wall sculptures. I had found a way to invent, but it was in an area I had never dreamed of.

How are your sculptures constructed?

All of my work is driven by constant-force springs, which use a two-spool set-up where a stainless-steel spring band is wound from one spool back against its natural coil direction onto a second spool. As the spring fights to return to its original form, it provides a fairly even torque over the full length of the band. This mimics the torque provided by a traditional clock-weight drive, but in a more compact form. The concept of a constant-force spring confuses many people, because they think of it as a constant-velocity spring motor – something that will turn a wheel at a constant rotational speed. That is not the case: the torque or force is constant, but the unregulated rotating wheel will just keep accelerating until the spring is fully unwound – often creating quite a mess!

So from a purely mechanical view, my sculptures are devices that regulate the unwinding of a spring. Over the years, I have invented quite a few different mechanisms to do this, starting with the concept of clock escapements and extending it to create longer, more active action cycles and random motion. I have two major advantages over clock designers: my works do not have to run for days and they do not have to keep time. Instead, my goal is to create interesting patterns of motion that keep moving (and entertaining) for hours.

How does your training in physics help?

It is essential to my career as a kinetic sculptor. Knowledge of basic mechanics is a necessity, but the analytical study and problem-solving skills that I developed as a physics student have been, if anything, far more important. The intense initial design period when I was visualizing the concept of spring-driven kinetic sculptures felt very much like the long days and nights at university when I tried to get my head round advanced physics concepts.

• www.woodthatworks.com

'Subtle defect' worry at LHC

By Hamish Johnston

Something to worry about: brown bars are the copper stabilizers

A few weeks ago Matthew Chalmers reported that Higgs-hunting particle physicists will have to wait until 2013 before the LHC reaches its maximum energy.

The nuts and bolts of why are described nicely in a new paper called Superconductivity: its role, its success and its setbacks in the Large Hadron Collider of CERN, which has just been published in Superconductor Science and Technology.

The paper — by CERN’s Lucio Rossi — includes a section called “Incident in sector 3-4” that describes in great detail the accident that took down the LHC in 2008. You can read exactly how an electrical connector failed — vaporizing a length of superconducting cable, heating the surrounding helium, which surged along the beam line wreaking havoc.

Could a similar disaster strike again? Rossi appears to say yes — “…a more subtle defect, related to a lack of continuity in the copper stabilizer, is now evident and is worrying since it is diffused around the machine”.

These copper stabilizers are part of an electrical circuit used to divert current from the superconducting cable if a fault occurs. Rossi is worried because at some connectors there is insufficient electrical contact between the cable and stabilizers — and between adjacent stabilizers. In the diagram above this trouble spot is labelled “Gaps with lack of Sn-Ag filler”.

If such a splice between cables fails — as one did in 2008 — the adjacent cable is heated and is no longer superconducting. If the cable is bare and there is a gap between stabilizers, current is forced to flow through the cable causing it to melt in a matter of seconds.

While the LHC has implemented a new system for detecting bad splices before they can cause damage, Rossi says that the gaps at the connectors could themselves be a problem. Warm helium from a minor problem elsewhere could, for example, heat the connector — triggering a similar disaster as occurred in 2008.

LHC scientists have devised a way of finding such gaps — but it works best when the LHC is warm. Half the accelerator was warmed up in 2008 for repairs and gaps were found and fixed. Most of the other half, however, was kept at 80 K and could not be thoroughly tested and repaired. As a result, Rossi believes that several gap defects could remain in the accelerator.

The upshot is that CERN will run the LHC in 2010 at the lower energy of 7 TeV, hoping that the connectors will hold. Then the accelerator will be shut down in 2012 for a year so all 10,000 connectors can be replaced. Finally, in 2013 protons in the LHC will collide at 14 TeV.

But the paper is not all bad news — it also describes how the LHC is at the pinnacle of superconducting technology. Here are a few superlatives:

– The accelerator has nearly 10,000 superconducting magnets

– The magnets are cooled by 130 tonnes of helium held at 1.9 and 4.2 K

– The accelerator contains about 15,000 MJ of magnetic energy

– 1200 tonnes of Nb-Ti superconducting cables were used to wind the magnets

– There is a 0.01% variation in field quality among the 1232 main dipole magnets

Molecular attraction keeps asteroids together

The strange shapes and composition of small asteroids could have a surprising origin – the heavenly bodies are held together by the same van der Waals forces normally associated with atoms and molecules. This is the claim of scientists in the US and UK who made the first detailed comparison of all the forces that could be involved in sticking asteroids together.

Understanding these forces could help scientists to work out how asteroids form and evolve – and even suggest how to deflect objects that threaten Earth. “This approach may also yield useful insights into other solar system environments, such as planetary rings and proto-planetary disks,” explained Daniel Scheeres, who was involved in the research along with colleagues at the University of Colorado and Michael Swift at the University of Nottingham.

Images sent back from space missions suggest that smaller asteroids are not pristine chunks of rock, but are instead covered in rubble that ranges in size from metre-sized boulders to flour-like dust. Indeed some asteroids appear to be up to 50% empty space, suggesting that they could be collections of rubble with no solid core.

Clinging on

Asteroids tend to spin rapidly on their axes – and gravity at the surface of smaller bodies can be one thousandth or even one millionth of that on Earth. As a result scientists are left wondering how the rubble clings on to the surface. “The few images that we have of asteroid surfaces are a challenge to understand using traditional geophysics,” Scheeres explained.

To get to the bottom of this mystery, the team made a thorough study of the relevant forces involved in binding rubble to an asteroid. The formation of small bodies in space involves gravity and cohesion – the latter being the attraction between molecules at the surface of materials. While gravity is well understood, the nature of the cohesive forces at work in the rubble and their relative strengths is much less well known.

The team assumed that the cohesive forces between grains are similar to that found in “cohesive powders” – which include bread flour – because such powders resemble what has been seen on asteroid surfaces. To gauge the significance of these forces, the team considered their strength relative to the gravitational forces present on a small asteroid where gravity at the surface is about one millionth that on Earth. The team found that gravity is an ineffective binding force for rocks observed on smaller asteroids. Electrostatic attraction was also negligible, other than where a portion of the asteroid this is illuminated by the Sun comes into contact with a dark portion.

Smaller particles get a grip

By contrast van der Waals forces – weak electrostatic attractions between adjacent atoms or molecules that arise from fluctuations in the positions of their electrons – seem to do the trick for particles that are less than about one metre in size. The size of the van der Waals force is proportional to the contact surface area of a particle – unlike gravity, which is proportional to the mass (and therefore volume) of the particle. As a result, the relative strength of van der Waals compared with gravity increases as the particle gets smaller.

This could explain, for example, recent observations by Scheeres and colleagues that small asteroids are covered in fine dust – material that some scientists thought would be driven away by solar radiation. The research can also have implications on how asteroids respond to the “YORP effect” – the increase of the angular velocity of small asteroids by the absorption of solar radiation. As the bodies spin faster, this recent work suggests that they would expel larger rocks while retaining smaller ones. If such an asteroid were a collection of rubble, the result could be an aggregate of smaller particles held together by van der Waals forces.

Asteroid expert Keith Holsapple of the University of Washington is impressed that not only has Scheeres’ team estimated the forces in play on an asteroid, it has also looked at how these vary with asteroid and particle size. “This is a very important paper that addresses a key issue in the mechanics of the small bodies of the solar system and particle mechanics at low gravity,” he said.

Scheeres noted that testing this theory requires a space mission to determine the mechanical and strength properties of an asteroid’s surface. “We are developing such a proposal now,” he said.

The work is described at arXiv: 1002.2478 and has been submitted for publication in Icarus.

Physics and bullying

Gordon Brown has recently been accused of bullying staff members. Credit: Downing Street

By Margaret Harris

Workplace bullying has become a hot topic in the UK lately, following allegations that Prime Minister Gordon Brown bullied members of his staff at No. 10 Downing Street. Leaving aside the (substantial) politicking behind these particular claims and counterclaims, the debate seems to hinge on a question that is as relevant to career physicists as it is to career politicians: what, exactly, constitutes bullying?

The UK’s Advisory, Conciliation and Arbitration Service (ACAS lists several examples of bullying and harassing behaviour. Some of them seem pretty obvious. Any manager — be it a Prime Minister or a PhD supervisor — who makes unwelcome sexual advances or spreads malicious rumours about an employee is clearly bang out of order, and ought to be severely reprimanded or sacked.

But other examples are less clear. “Overbearing supervision” is on the list, as is “ridiculing or demeaning” someone. Neither of them sound like much fun, but different people react differently to criticism, and it’s at least arguable that one person’s “overbearing supervision” is another’s “making sure the job gets done right”.

There are some reasons to believe that academia is particularly prone to bullying, as one commenter on a recent BBC story suggested. The apprenticeship system for PhD students and early-career researchers gives senior academics a lot of power and influence over their junior colleagues. It also makes it difficult for victims of bullying to walk away from a bad situation, because chances are they’ll have to either start over or leave academia entirely.

But I wonder whether there’s something more subtle going on with physics in particular. The fact is that quite a few of history’s great physicists — the people many of us regard as our scientific heroes — weren’t exactly great managers. I enjoy stories about Feynman’s skirt-chasing as much as anyone, but I’d have thought twice about being his PhD student. Bohr frequently drove Heisenberg to tears. And there are plenty of horror stories out there about lesser scientists; my favourite (unconfirmed) one is of a Nobel laureate who allegedly went around urinating in other people’s experiments so that they wouldn’t work.

Can we separate these physicists’ great achievements from their personal flaws? Certainly. But perhaps we should think twice about relating these anecdotes with such gusto. After all, what was Pauli’s famous “not even wrong” jibe if not “ridiculing or demeaning” to the hapless lecturer on the receiving end?

You stay classy, San Diego

Just north of the border

By James Dacey

Well, here at the San Diego Convention Center people are starting to dismantle things around me so looks like the AAAS conference is well and truly over for this year. It’s been a fun five days and I hope this blog has given you a reasonable flavour of the theme Bridging Science and Society.

Next year’s meeting will be in Washington D.C. where the focus will be Science Without Borders – a celebration of all things multidisciplinary. If you’re interested in taking part then they’re already taking submissions for symposia.

Right, after all the big ideas and dashing around this huge convention centre, I’m off for some much needed relaxation. I leave you with a few snapshots of the hosting city.

For those of you haven’t seen the film Anchorman, I apologize but I just can’t resist it – You stay classy, San Diego.

San Diego Convention Center, a large host

Tribute to the US naval military

Waterfront, alongside San Diego Bay

Can anybody identify this bird?

The lively Gaslamp quarter

‘Physicists are modellers too, but lousy modellers’

No flies on Stephen Schneider

By James Dacey

This great quote came on the final morning here at the AAAS conference in San Diego. Stephen Schneider, an environmental scientist at Stanford University, was lashing out at all forms of climate change denial including those physicists who make a sport of pointing out uncertainties in climate models.

Schneider’s point is that when physicists make laws and theories by studying the relationships between pairs of data, they are still modelling – just with much less data.

The main thrust of Schneider’s talk – delivered with a relish that could have garnished the Mexican burger I had last night – was that climate scientists should not shy away from entering the public debate on climate change. “Because I have a Ph.D. is not a reason to “hang up my citizenship at the door” of a public meeting—we too are entitled to personal opinions,” he said.

Schneider believes that the media’s representation of climate science is being increasingly shaped by the scientifically unqualified and “old men” who overstretch their dwindling expertise.

Breathe easy, the LHC still won't swallow the Earth

The CMS experiment

By James Dacey

“Of the billions who tuned in for the switch-on, I suspect that many were only interested in seeing whether or not we would be blown to smithereens.”

The words there are those of John Ellis, a senior research scientist at CERN, talking just now at the AAAS conference in San Diego about why the Large Hadron Collider (LHC) was never really going to destroy the planet.

I was half expecting (rather, hoping) that the talk would be gate-crashed by a gang of doomsday mongers; or perhaps even Walter Wagner, the high-school physics teacher who filed a federal lawsuit in the US District Court in Honolulu in 2008 to prevent the LHC from starting up.

Alas, they all failed to show.

Ellis, who has worked on several LHC experiments, gave an eloquent description of how CERN responded to all the scaremongering. It was the usual stuff, but it was interesting to here of how Ellis’ colleagues had taken “months” out of their research to calculate the exact nature of the tiny black holes – the ones that almost certainly wouldn’t be produced, and even if they were, would possess the “energy of a fly”.

If you’ve never really trusted those CERN guys, or you’re just really bored, you can find extensive details of all the LHC’s safety precautions here.

Despite his sensible words, I’ve got to say I was a bit surprised by Ellis’ reply to my question over whether physicists, when talking with the media, should stop discussing doomsday scenarios in terms of statistics and just say “no – there is no chance”. “I’m a scientist,” he said. “We deal in probabilities.”

Ellis was speaking as part of a larger discussion entitled Organizer: Doomsday Versus Discovery, in which other speakers discussed how the media have reacted to the developments at CERN and the historical and philosophical issues surrounding the fear of big science.

Researchers! Join the Twitterati! Or perish!

The Cocktail Party, 1965. Alex Katz

By James Dacey

It’s been compared to a cocktail party where multiple conversations, all taking place at once, result in that familiar cacophony of chitchat. Some people thrive in this environment, while others feel jarred, but eventually we all drag ourselves along to one because we know that’s the real place to hear the interesting stuff for our careers.

Researchers need to get themselves onto Twitter pronto because it is fast becoming the place to find out the breakthroughs in your research field. That was the take-home message from Bora Zivkovic, the online community manager of the journal PLoS ONE, who was speaking today on the penultimate morning of the AAAS conference in San Diego.

Zivkovic, who was an entertaining speaker with a nice dry sense of humour, admits that the popular microblogging site does play host to a lot of inane chitter. He insists, however, that so long as you are selective about whom you “follow”, you can build up a very helpful bunch of online colleagues. He is a bioscientist by training, and described how he uses Twitter each day to catch up on how colleagues’ research is developing and to see what key publications and events are taking place that day.

One flabbergasted member of the audience took issue with Zivkovic, saying that with “only 24 hours in a day” there is simply not enough time to uphold a professional reputation online. Zivkovic conceded that not every every social networking site is right for everyone, but he is convinced that Twitter is different, arguing that its simplicity and benefits make it worth the investment of time. “It’s just like e-mail – in 10 years you won’t remember what it was like to have lived without Twitter,” he said.

At the end of the session, entitled Science 2.0: From Tweet Through Blog to Book, you could be forgiven for thinking that Zivkovic is being paid by Twitter to say all these nice things about their site. I don’t think he is, but he’s certainly infatuated with the online cocktail party. So join him there or be square, maybe.

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Stamping your mark on science