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Home » Page 1565

Governing science

Many scientists see US President George W Bush as being bad for science, as has been made clear in numerous books, editorials and Congressional testimony. Although these scientists say that federal funding for science is at a reasonable level, they claim that his administration has rejected the advice of its own scientists, suppressed unfavourable reports, allowed ideologies to damage the infrastructure, and used celebrities as consultants. Apart from three of the 10 Republican presidential candidates – Sam Brownback, Mike Huckabee and Tom Tancredo – who do not believe in evolution, any replacement might seem preferable.

Be careful what you wish for. Consider the record of Bill Richardson, one of eight or so Democrats seeking their party’s nomination, to be decided next August. Richardson, 59, currently the governor of New Mexico, served in the Clinton administration between 1998 and 2001 as secretary of the Department of Energy (DOE), which oversees 10 national labs. While Richardson is lower in the polls than his Democratic rivals Hillary Clinton and Barak Obama, his administrative experience and Hispanic roots earn him a following. Yet during Richardson’s tenure at the DOE, two episodes are disturbing.

Troubled times

One episode is the case of Wen Ho Lee – a nuclear engineer at the Los Alamos National Laboratory. In 1999 media reports charged that Lee was spying for the Chinese government. Although the charges were based on information known to be false, Richardson had Lee fired and was later cited as having leaked Lee’s name to reporters (although Richardson denies this). Lee was arrested, chained in solitary confinement and threatened with execution. He eventually won a case against the DOE and other agencies for violation of privacy. Richardson has declared that he acted responsibly, but others saw him as pandering to the media crusade and being guilty of targetting members of specific ethnic groups – and the Federal judge who oversaw the case publicly apologized to Lee.

The second episode concerns the High Flux Beam Reactor (HFBR) at the Brookhaven National Laboratory (BNL) – one of most important neutron sources in the world. Its innovative design was partly devised by its senior user, Julius Hastings, and its research ranged from cancer cures to superconductivity. The HFBR was closed when Richardson took over. While the reactor was performing safely, its spent-fuel pool was leaking a small amount of tritium-containing water. A decision procedure for a restart had been worked out that included a new Environmental Impact Statement (EIS). Although the leak was confined to lab grounds and posed no threat to employees or the local community, it fostered an outcry among the media and anti-nuclear activists (2001 Hist. Stud. Phys. Bio. Sci. 32 41).

An antinuclear group, members of which included celebrities and Democratic party fundraisers such as supermodel Christie Brinkley, publicly campaigned against the restart in ways that Democrats would now call “Swiftboating” – the term means an unfair attack and derives from an episode during the 2004 presidential campaign. The attacks used material that BNL scientists found distorted and even dishonest, including the circulation of false rumours of the incidence of cancer clusters around the lab.

Richardson met with the antinuclear group and agreed to its demands to extend the comment period for the EIS. Hearing of this, Hastings called Richardson’s office to ask for a meeting. Hastings was refused. Meanwhile, the completed EIS draft concluded that “the environment and public health and safety would be protected” in an HFBR restart – but the DOE refused to release the document.

Instead, Richardson met again with Brinkley’s group. According to a report in George magazine, a then-popular political periodical, Brinkley “reminded Richardson that his aspiration to be Al Gore’s running mate [in the 2000 Presidential election] – a job he hadn’t been coy about lobbying for – would be seriously compromised if he didn’t acquiesce”. According to the article, Richardson was left speechless.

Richardson then terminated the HFBR, thus aborting the carefully arranged restart procedure. He did not bother to tell the lab; officials only learned of his action through the media. Scientists were outraged – not just by the decision and the lame reasons Richardson offered for it, but also for treating eminent scientists as bumpkins who need not be consulted or even informed.

Richardson denies Brinkley had influenced his decision. Brinkley did not think so, and appeared on talk shows claiming responsibility for the HFBR’s demise. Richardson then came to Long Island to accept an award from Brinkley’s group, which was handed out at a pop concert given by Brinkley’s ex-husband Billy Joel.

“Remember the HFBR!” is unlikely to become a popular rallying cry. Richardson is surely banking that the public has forgotten his handling of the HFBR and in any event would not care much about the closure of a research reactor. Yet to those who do remember, the episode raises troubling questions. Would a Richardson administration be better for science than the current one? Would activism and ideology rule science policy? Would experts be consulted, or would fundraisers and celebrities lead officials by the nose?

The critical point

In the upcoming US presidential election, such questions will be important. For the Bush administration, inadvertently, has done a wonderful thing for science. It has shown the importance of political leaders who respect science: its infrastructure, its instruments, its experts and its data. It has shown the need to let facts dictate policies rather than vice versa. It has shown that robust science is essential to the safety and welfare of democracy, and of the planet.

When word surfaced that George W Bush had consulted blockbuster author Michael Crichton about global warming, scientists saw it as a cruel joke. We must therefore be equally critical of other potential presidents. The abuse of science by the left is as dangerous and despicable as that by the right. Politicians who damage our carefully assembled and precious scientific infrastructure for political gain cannot be taken seriously.

Life in the line of fire

For the past 10 years I have been working as an instrument scientist at the Institut Laue-Langevin (ILL) in Grenoble, France. Life in the French Alps is certainly a far cry from my origins in the flatlands of Victoria in Australia, although the quality of the wine is comparable. I came to Europe after completing a physics degree at the University of Melbourne and a doctorate in condensed-matter physics at Monash University. Initially I worked in the UK at Oxford University on neutron and X-ray scattering experiments, but then, just before my contract ended, I was offered a job at the ILL. Although I have now spent more time working here than on both my degrees and my postdoc put together, it feels much shorter!

The ILL is a high-neutron-flux research facility and is arguably the most powerful source of neutrons in the world. More than 40 instruments for experimental science are attached to the nuclear reactor that produces the neutrons. Most of the instruments are used for neutron scattering, in addition to four for nuclear physics, one for radiography and one for interferometry. All the instruments are different, although there is some overlap between the science that can be done with them. I like to think of the institute as a giant toolbox where scientists can choose the right tool to solve each problem that comes along.

Three jobs in one

The ILL employs about 60 full-time scientists, and our work is roughly divided in to three parts. First, we each have responsibility for maintaining and developing one of the instruments. I work on D17, which is a neutron reflectometer that is designed to measure the properties of surfaces and subsurface interfaces buried inside a sample. The instrument is always changing as we think of ways to improve it – from boosting the neutron intensity to developing the software used to run it. The science done with D17 is very broad in scope, ranging from studies of biological membranes to chemical catalysis and magnetism, so careful thought and lateral thinking are required to optimize each experiment.

Second, instrument scientists have “local contact” duties, which means helping visiting academics to carry out and interpret their experiments. The ILL welcomes about 2000 scientists each year who, between them, perform about 750 experiments during that time. Anyone can propose an experiment at the ILL, but they must be approved through competitive scientific evaluation. Once a proposal is accepted, the researchers are assigned “beam time” to carry out the experiment. Neutron-scattering experiments typically take between two days and two weeks, depending on the instrument and the type of experiment, and the visitors want to get the best use out of every available neutron.

This aspect of the work can be very rewarding, as my colleagues and I are exposed to new and exciting ideas, and get to meet many people. We can act as local contact on any of the instruments at the ILL. As well as D17, I often act as the local contact for the “three-axis spectrometers”, which are instruments particularly suited for measuring structural and magnetic vibrations in crystals. Being able to work on other instruments means that I can collaborate closely with visitors as they move around the facilities at the ILL – far more satisfying than being confined to “one-off” experiments on a single instrument.

Finally, all instrument scientists have their own research programmes. Ultimately, the ILL is judged on the science that it produces, and we are encouraged to publish our work regularly. My research is in the measurement of magnetic structures and dynamics. A neutron has no electrical charge, but it does have a magnetic moment that will interact with any magnetic induction in a sample, which makes neutron scattering a sensitive probe for experiments in magnetism. One of my research programmes looks at the magnetic structures of iron-based metallic glasses, which are poorly understood but are used widely in industry for everything from transformer parts to magnetic read-heads. Another programme looks at magnetic structures and vibrations in low-dimensional materials, such as thin magnetic films. Research is probably the most challenging and the most fun part of my work, as I am free to use my imagination and pursue the science that I find the most interesting.

A career with neutrons

While the job of instrument scientist has three parts, the division of time between them can fluctuate enormously. You must fight to make time for all three, and sometimes it feels like you do, in fact, have three jobs! In particular, when there are problems on the instrument or visitors needing help, it can be very difficult to find time for your own research. The reactor runs for four cycles of 50 days each year, and during these cycles it can be very busy indeed. Between cycles, there is more time to concentrate on analysing data, writing journal articles and attending conferences, although any major modifications to the instrument must also be made while the reactor is shut down. Finding time for holidays during all this can lead to friction, particularly when trying to negotiate with one’s family.

Nevertheless, being an instrument scientist means having a great job, tremendous fun and plenty of career opportunities. A few years ago, neutron scattering was considered to be in decline, with many of the older neutron sources being closed down. However, there is a new wave of investment with the building of many new and powerful neutron sources all over the world, and also with new instrumentation at established sources like the ILL. Instrument scientists are in great demand, so it is an excellent time to be starting a career with neutrons.

A good way to begin is to try neutron experiments during doctoral work. I used neutron scattering during my PhD for magnetic- structure determination, which taught me the basics and introduced me to many other people who use neutrons, some of whom I now work with on a regular basis. A background in physics is useful for an instrument scientist, as the techniques are all physics-based, but centres like the ILL have excellent opportunities for multidisciplinary science and also employ instrument scientists who are trained in chemistry or biology.

Am I still enjoying working at the ILL after 10 years? In Nick Hornby’s novel How To Be Good, the main character compares science and the arts, saying one is “all empathy and imagination and exploration and the shock of the new, and the outcome is uncertain”. That is how I feel about my job, every day. In fact, Hornby’s character was actually talking about the arts, going on to say that science “presses this button, then that one, and bingo! Things happen. It’s like operating a lift”. Believe me, this is nothing like what we do, and just goes to show that Hornby should spend more time in a physics lab.

Once a physicist: Chandrika Nath


How did you first get interested in physics?

It was mainly through Patrick Moore and the Open University TV programmes. Even when I was seven, I would sit in front of Open University for the whole of Saturday morning watching really dire programmes about physics and finding them fascinating. Then, when I was 10, my dad got me a telescope and I started looking at the sky and wondering about the size of the universe. And finally, I didn’t want to become a medical doctor like every other Indian daughter I knew.

Where did you study physics and how much did you enjoy it?

I went to Imperial College London as an undergraduate and the course was really good – loads of variety and well taught – but I didn’t enjoy the university itself that much. At the time only one in 20 students were women and being a student in central London isn’t that much fun because no-one can afford to go out and everyone lives miles apart. After graduating, I decided to take a gap year and somehow got from Mexico to Alaska in the space of one summer, mainly by hitchhiking. Then I went to teach in a school for blind children in India. I also worked at Texas Tech University in Lubbock on calorimeter design for the Superconducting Super Collider – hopefully I wasn’t responsible for its demise!

What did you do next?

I went to Oxford University to do a doctorate in particle physics and I enjoyed that university experience much more. Originally, I hadn’t wanted to go to Oxford because someone told me it was like an extension of a girls’ private school, but by that time I was 23 so it was easy enough to escape that side of things. I was based in Hamburg for a couple of years, working at the HERA accelerator and studying theoretical physics in German, which was quite an experience. I’ve completely forgotten the title of my thesis – it was something to do with instantons, though I don’t even remember what those are now.

How did your career develop from there?

In my gap year I ended up in Alaska and I decided then that one day I wanted to study ice. I had a grand plan to make my own way across the Bering Strait. Then one day I was flicking through New Scientist magazine and came across an advert for a job with the British Antarctic Survey (BAS). I didn’t expect to get it, but I did, and decided that it was an acceptable alternative to the Bering Strait. I spent four years with the BAS studying how crevasses form, including five months in the Antarctic living in a tent with three blokes. Having gone from relativistic quantum mechanics back to Newton’s laws of motion, I was intrigued to find that the macroscopic world holds as many mysteries as quarks and gluons.

How did you make the move into science communication?

At the end of my time at the BAS I did a media fellowship with Roger Highfield at the Daily Telegraph. I was vaguely thinking about becoming a journalist and then a job came up at the Parliamentary Office of Science and Technology (POST). I was intrigued by the idea of working within parliament, and it satisfied my need to not have to turn things around on really short timescales. POST’s job is to provide MPs and peers (members of the House of Lords) with balanced information on policy issues that relate to science and technology. Very few parliamentarians have a science background so they need an objective, understandable source of information to help them scrutinize government policy. My biggest piece of work to date has been a 200-page report “Assessing the risk of terrorist attacks on nuclear facilities” but I’ve also worked on reports covering military satellites, digital forensics and online privacy.

What are the main differences between working in policy and in research?

They’re completely different – I don’t think there are any similarities. But if you’ve been a researcher, you apply a lot of the skills you already have, so in a way you make the similarities. All the years of training as a scientist, documenting my work thoroughly and thinking logically are really useful. When you’re doing science, you are always wondering what else there is that you haven’t thought of. You never see something as an answer, just something that raises more questions. I think that pedantry is what makes me good at what I do now.

Reflecting symmetry

Why Beauty is Truth by Ian Stewart, a mathematician at the University of Warwick in the UK, is a historical account of the evolution of mathematics into modern physics right up to the era of superstrings. It traces the development of the mathematical conceptualization of symmetry and even provides some new and intriguing interpretations of historical events, such as the death of French mathematician Evariste Galois in a duel in 1832.

Stewart begins with the ancients: the Babylonian development of a modern (base six) number system; and early treatments of the algebraic problem of solving quadratic equations. As the historical tour unfolds, we see both the bizarre cult of Pythagoras and the Persian mathematician Omar Khayyam’s development of the solution of a cubic equation. Then we move on to the Renaissance and the Enlightenment, as we trace the quest for mathematical solutions to higher-order algebraic equations, before arriving at the problem of solving quintic (i.e. fifth-order) equations.

Thus begins the tale of the young Frenchman Galois. He was a radical, revolutionary and energetic man – one can visualize Tom Hulse’s portrayal of Mozart in the film Amadeus to capture a glimpse of what might have been Galois’ energized persona. Galois evolved sophisticated new methods for solving quintic equations by “thinking outside the box” and for the first time introducing symmetry to analyse an algebraic problem. Stewart gives a succinct account of who Galois was before going on to speculate about how he came to meet his tragic end at the age of just 21.

According to folklore, the radical Republican Galois was shot by Pescheux d’Herbinville, who may have been an assassin hired by the French Crown. Allegedly, Galois had been entrapped into a love triangle with d’Herbinville’s wife, which led to the duel. However, Stewart largely debunks this interpretation. While a romantic impetus for the event persists, he suggest that the opponent in the duel may in fact have been an old friend of Galois’, perhaps Vincent Duchatelet, a young compatriot in love with the same woman. The event was gruesome – a single bullet to the stomach, usually fatal in those days. Contrary to the legend, Galois did not succumb on the field of honour in a matter of hours, but instead died the next day in a Paris hospital due to peritonitis, and refusing the last rites.

Galois left behind notes on his solutions to the quintic equations, incorporating symmetry, which spawned a revolution in mathematics. The material made its way to the great Joseph Liouville and was presented to the French Academy of Sciences. Thus emerged the conceptual foundation of symmetry as an algebraic system: the codification of symmetry into what mathematicians call group theory, which now envelops almost all branches of mathematics, from number theory to topology. The book then tracks the further expansion of modern mathematical thought through William Rowan Hamilton, Niels Abel, Sophus Lie and Elie Cartan. Finally, at the dawn of the 20th century, symmetry and group theory became part of modern physics.

Albert Einstein was the first physicist to think in the modern style of symmetry, and Stewart covers the development and implications of special and general relativity through their underlying symmetry principles. Today, group theory underlies the Standard Model of particle physics through the concept of local gauge invariance. However, the book underplays the famous theorem of the German mathematician Emmy Noether that connects symmetry to conservation laws, and which Einstein and David Hilbert so championed. The author handles well a vignette of quantum theory and the first proposal of hidden extra dimensions of space–time by Theodor Kaluza and Oscar Klein.

Finally we are brought up to date with today’s speculative ideas of supersymmetry and superstring theory. Stewart gives us a personal view of the towering figure of modern theoretical physics, Edward Witten. Interestingly, Stewart hints that George McGovern’s failed US presidential campaign and the subsequent election of Richard Nixon in 1972 led Witten to abandon a career as a political journalist and instead to go to Princeton University to obtain a doctorate in physics. Witten has been the clear leader of theoretical physics for 25 years (often compared to Einstein) and is a recipient of the Fields Medal for his contributions to knot theory.

String theory awaits definitive test by experiment. Such a test will come soon with the discovery of (or failure to discover) supersymmetry at the Large Hadron Collider at CERN, due to switch on next year, although some will dissent with that view. It is disappointing that Stewart fails to connect to this timely enterprise by which physicists will take their next step into the depths of physical reality. Indeed, the book loses its focus somewhat at the end.

The format of history intermeshed with mathematical concepts is a popular approach nowadays. Why Beauty is Truth requires some prior interest in the subject, and it lacks the edge of Simon Singh’s Fermat’s Last Theorem. However, it will be a satisfying read for anyone who wants to delve into the historical development and conceptual foundations of modern mathematics and physics.

Superlens avoids absorption

Superlenses — lenses that in theory can have unlimited resolution — avoid the diffraction-related limits on the resolution of normal lenses by capturing the special “evanescent” waves that exist close to a sample’s surface. To do this they must be made of a material with a negative refractive index, but so far physicists have struggled to find such a material that works for visible light but doesn’t absorb too much light.

Ronald Walsworth from Harvard University and colleagues from University of Connecticut and the Technische Universität Kaiserslautern say that absorption can be almost eliminated using a new technique called electromagnetically-induced chirality (EIC) — a variation on an established technique called electromagnetically induced transparency (EIT).

In EIT, the transmission of a “probe” laser pulse through a medium is controlled by a second “pump” laser pulse. With the pump pulse off, the probe momentarily excites atoms to a higher energy state before they fall down again and re-emit the light in random directions. But turn the pump pulse on and the atoms are pre-excited to a different energy state, leaving the probe pulse to pass through that atoms as if they were transparent.

To achieve EIC, Walsworth and colleagues propose a more complicated arrangement of energy levels that would not only make a medium transparent, and hence non-absorbent, but would also make the electric and magnetic light fields interact. Such “chirality” would make a negative refractive index practically achievable by reducing the density of material required.

The other advantage of the proposal is that, by changing the intensity of the pulses, the strength of the negative refraction can be precisely tuned. According to Walsworth, this would be important for making lenses that do not distort images.

Walsworth told physicsworld.com that experimental versions of his idea are being pursued by colleagues of his at Harvard.

Chinese law to promote honest research

China’s current law on science and technology progress, which has been effective since 1993, states that institutions can “enjoy decision-making power in their conduct of research and development” and that the government should “protect their legal rights and interests against any encroachment.” It also notes that there should be sanctions for funding bodies that make deliberate attempts to falsely appraise research.

However, there is no specific statement in the law to protect scientists from having their funding withdrawn if they fail to make any breakthroughs with their research. For this reason, some scientists in China worry that this encourages researchers to fabricate results rather than report failures. Earlier this month, Chinese state media reported that 13 scientists had been blacklisted for falsifying scientific data.

According to the Xinhua news agency in China, legislators are suggesting that an amendment to the 1993 law should state: “Scientists and technicians, who have initiated research with a high risk of failure, will still have their expenses covered if they can provide evidence that they have tried their best when they failed to achieve their goals.”

Chen Nanxian, a member of the National People’s Congress standing committee in China, said that it should also be amended to encourage scientists to report all failures so that others can learn from the experience.

Xinhua reported that Bai Chunli, the vice-president of the Chinese Academy of Sciences, was concerned about the “atmosphere of fear” surrounding failure in scientific field. “It’s difficult to make achievements in independent innovation if the scientific research departments and scientists don’t tolerate failures,” Chunli told the agency.

Most scientific research in China is funded by the government through bodies such as the Ministry of Science and Technology or the National Natural Science Foundation of China, and compared with the US or the UK there is less funding from the private sector.

IBM targets single-atom data storage

Hard disk drives work by storing data in small magnetic domains on a thin film but their capacity is limited by how small the domains can be made. Indeed, when domains become smaller than several tens of nanometres across, thermal fluctuations cause the direction of magnetization to change in a random fashion. The resulting “superparamagnetism” makes it impossible to store data.

Some physicists believe this “superparamagnetic limit” could be beaten by storing data on tiny nano-particles comprising as few as one magnetic atom surrounded by non-magnetic atoms. Now, Andreas Heinrich and colleagues at IBM’s Almaden Research Center in California have made an important step in this direction by placing a single atom on the surface of a copper-nitride film so that its magnetic moment points along one direction. According to Heinrich, the team are the first to see this magnetic anisotropy in just one atom.

By using the STM to study the atom and its surroundings, the researchers concluded that the anisotropy was caused by interactions between the magnetic atom and its neighbours.

Heinrich told physicsworld.com that the effect could someday be used to create a device with a storage density 1000 times greater than the hard drives of today.

However, he cautions that much more research will needed before such a device could be built. For example, team has yet to show that data could actually be stored and retrieved using a single atom. They are currently studying a number of different magnetic atoms and substrates to find a system in which data could be read and written using the tip of a STM.

Another problem is that the measurements were made at very low temperatures of about 0.5 K, which would be impractical for commercial data storage systems. Heinrich said that the team would continue to work at very low temperatures while perfecting their read and write techniques.

Molecular logic
In the same issue of Science another team at IBM report a breakthrough in the use of single molecules as logic devices, which could someday be used to make extremely small and powerful computer chips. Peter Liljeroth and colleagues at IBM’s Zurich Research Laboratory showed that a single molecule of naphthalocyanine can be switched between “on” and “off” states without affecting its shape. While researchers at IBM and elsewhere have already switched single molecules, those molecules changed their shape and would therefore be unsuitable for building logic gates for computer chips or memory elements. The team is now trying combine a number of the molecules to create a logic device (Science 317 1203).

Warm ice could improve medical implants

Thanks to their resistance to wear, thin diamond coatings are being used in a growing number of medical implants such as artificial heart valves, prosthetics and joint replacements. However, diamond is limited in its potential because it is more likely to cause blood clotting and tissue abrasion compared with other materials.

Wissner-Gross and Kaxiras think these problems could be solved if a layer of sodium atoms were covalently bonded to the surface carbon atoms in diamond beforehand. By encouraging dipole interactions with the surface, this sodium layer would allow a layer of water over 2 nm thick to stay frozen on the surface, thus providing a biologically-compatible shield from the diamond beneath. Although experiments have produced nanoscale ice at room temperature before, this theoretical result shows that it could have a practical application.

The Harvard team came to this conclusion after simulating the attractive and repulsive interactions between atoms at the surface of the film. From this simulation they could extract the Lindemann parameter, which shows — at a certain temperature — how the size of the relative motion of water atoms changes over time. If the Lindemann parameter steadily increases after the simulation is started, it shows that the order in water’s structure is reducing, and therefore that the water is melting. If on the other hand it tails off to a steady value, the water stays frozen.

Wissner-Gross and Kaxiras found that the unusual amount of dipole interaction between the water molecules and the diamond-sodium surface meant that an ice film 2.6 nm thick could be sustained at 25°C, and that at 37°C — that is, at humans’ body temperature — the thickness could be 2.2 nm.

According to the American Physical Society, which publishes the journal in which the researchers’ study appears, a short film of their simulations won them the 2007 Materials Research Film Festival.

Physicist models Spiderman suit

The stickiness of geckos and spiders comes from thousands of tiny fibres on their feet that grab hold using a combination of three effects – capillary forces arising from a thin layer of liquid water between the fibres and the surface; van der Waals attraction between the fibres’ molecules and those on the surface; and Velcro-like interlocking of the fibres with tiny structures on the surface. Unlike glue, these effects still allow the feet to easily detach from the surface and thus allow the creatures to walk, and they also seem to prevent the feet from accumulating dirt.

Pugno claims that gloves and boots for humans employing the same effects could be made by weaving millions of carbon nanotubes – which are each only about 10 nm thick – into threads about 1 cm thick. The thickness of the individual nanotubes and their spacing could be chosen to make the thread transparent to visible light, which Pugno claims would make them invisible.

The nanotubes at the end of a thread would be splayed in a fan-like structure, which would ensure that there were millions of contact points between the thread and a surface in order to maximize its stickiness. Pugno claims that a combination of capillary, van der Waals and mechanical forces would allow one such thread to support the weight of a man (70 kg) and that a pair of gloves covered in them could support over 1000 kg.

Pugno says that the material would be self-cleaning because carbon nanotubes are hydrophobic and therefore shed water, which takes dirt with it. Because adhesion involves million of tiny sticking points – each of which is relatively weak on its own – Pugno believes that the material could be peeled off the surface with a minimum of effort, provided the user was specially trained in the required hand motions.

Pugno even goes so far as to suggest that the material could be made into a sticky and invisible web that could be used to capture villains. Strains on the material caused by a struggling victim would change the material’s optical properties, rendering it visible to an aspiring Spiderman.

Although the idea of a Spiderman suit may seem far fetched, several research groups have already made sticky materials inspired by geckos – using polymer fibres rather than nanotubes. Also, researchers in the US have made fan-like structures from carbon nanotubes, which Pugno believes could be used in his suit.

Polaron melting heralds colossal resistance

Nearly 15 years ago, two groups working independently discovered that the electrical resistance of manganese oxides called manganites dropped by several orders of magnitude when the materials were exposed to a magnetic field. Dubbed colossal magnetoresistance (CMR), the effect is much different than giant magnetoresistance, which is relatively well understood and involves changes in resistance of several tens of percent. However, very little progress has been made in understanding CMR and the related effect of colossal electroresistance (CER), which occurs when some manganites are exposed to external electric fields.

Physicists had suspected that CMR and CER are related to polarons, which are charged quasiparticles that arise when conduction electrons and vibrating atoms (phonons) in a solid interact. In the absence of an external electric or magnetic field, electron-phonon interactions are thought to be strong enough to localize the polarons in an ordered “solid” that gives the material a high resistance.

However, an applied field is thought to weaken the electron-phonon interaction, allowing the polarons to move around much like a liquid. In some cases, the polarons strongly delocalize and move so freely that resemble the conduction electrons in a metal, explaining the 1010 drop in resistance seen in some manganites.

Now, a team including Christian Jooss at the University of Goettingen in Germany and Yimei Zhu from the Brookhaven National Laboratory in the US has confirmed the role of polaron “melting” in colossal resistance by watching the resistance of a manganite sample drop as its polarons transformed from solid to liquid.

The team used the tip of a scanning tunnelling microscope (STM) to apply an electric field to a small region of the sample and also to measure the resistance in that region. The tip was brought into contact with the sample and several volts was applied to create an electric field. The resistance of the sample could be determined by measuring the current flowing between the tip and the sample. At the same time a transmission electron microscope (TEM) was used to perform electron-diffraction measurements which confirmed that solid polarons in that region turned to liquid when a sufficiently large field was applied.

Although their experiments focussed on CER, the team are confident that their findings with help further the understanding of CMR as well. The researchers also believe that their work could make it possible for CER to be used to create resistive -random access memory (RRAM) devices, which are currently being developed by several chip makers. In a RRAM, data are stored in bits that can be switched between a very high resistance state and a very low resistance state. This simplifies the circuit design, shrinking the size of individual memory bits and allowing the data to be read and written hundreds of times faster than conventional memories.

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