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Brazil and Spain top the table

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Ibero-America Courtesy: Wikimedia Commons

By James Dacey

Academic institutions in Spain and Brazil account for nearly 70% of all scientific papers from Ibero-America published during the period 2003–2008. This political region incorporates Spain, Portugal and countries in the Americas that are former colonies of these two European nations.

The study, carried out by the SCImago Research group, found that Spain and Brazil each produced around 200,000 papers during this period, while Portugal was lagging in third place with just 50,000.

There are nearly 670 higher-education institutions within Ibero-America, with nearly 50% of these in Brazil, Colombia and Spain. Colombia’s relatively modest scientific output – just 9792 papers – is attributed to the country’s high number of small academic institutions.

The study also ranked the nations on other factors, including quality of publications (based on citations) and extent of international collaboration.

The full report (in Spanish) is available here.

Jinxed isotope reactor could soon be running

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NRU could be up and running soon

By Hamish Johnston

The shortage of medical isotopes caused by the year-long shutdown of Canada’s NRU reactor could soon be over.

Atomic Energy of Canada (AECL) – which operates the 53-year-old facility in Chalk River, Ontario – will appear before the Canadian Nuclear Safety Commission on 28 June to ask permission to restart the reactor.

If it gets the thumbs up, AECL says that isotope production could resume by the end of July.

Over the past few years the supply of Mo-99, which is used to make the medical isotope Tc-99m, has been threatened by two safety-related shutdowns of the ageing reactor. Normally, NRU supplies North America with Tc-99m and accounts for a significant chunk of world production.

The first shutdown began in December 2007 and lasted one month. The second started in May 2009 and is ongoing.

You can read more about how AECL plans to restart NRU here .

‘Dark pulse laser’ could improve telecoms

A new type of laser that emits “dark” pulses could provide better signals for telecommunications, according to physicists in the US who have created the device. The dark pulses, which consist of intensity dips in an otherwise continuous beam of laser light, are effectively the opposite of the bright bursts in a normal pulsed laser.

“The laser emits a brief pulse of darkness, if you will,” explains one of the researchers Richard Mirin, who is at the National Institute of Standards and Technology (NIST) in Boulder, Colorado. “And so you can think of it as a continuous-wave laser that has a really fast shutter in front of it.”

Dark lasers are not entirely new. For some 20 years, physicists have been able to create so-called dark soliton lasers. Solitons are light pulses that propagate without spreading, and are often used in fibre optics. Their dark counterparts are simply gaps in a continuous beam that do not spread either. But dark solitons are difficult to create and, when they are created, it is done outside the laser using a combination of tricky pulse-shaping techniques.

The new dark pulse laser, on the other hand, forms the dark pulses inside the laser itself. “We believe ours is the first example of a direct generation of a dark pulse,” says Mirin.

Quantum-dot diode laser

We believe ours is the first example of a direct generation of a dark pulse Richard Mirin, NIST

Mirin, whose colleagues work at NIST and JILA, a joint institute of NIST and the University of Colorado at Boulder, based his dark pulse laser on a standard quantum-dot diode laser. This type of device contains a tiny junction between a positively doped semiconductor (p-type) region, which has holes in its normal electronic structure, and a negatively doped semiconductor (n-type) region, which has a surplus of electrons.

When an electric current is driven through the junction, electrons and holes recombine inside the quantum dot, releasing energy in the form of light. This light is amplified using an adjacent cavity, thereby generating a laser beam.

Negative solutions

Quantum-dot diode lasers can be made to produce pulsed or “mode-locked” light rather than continuous light by tailoring the cavity, and this is governed by the Haus equation, named after the late Slovene-American physicist Hermann Haus. Pulses are described by solutions to the equation, which includes terms that relate, for example, to current injection and efficiency. In the past, researchers have generated bright pulses by considering the positive solutions to the equation. But now, Mirin and colleagues have looked at the negative solutions to generate dark pulses.

For tests, the NIST/JILA team built a quantum dot from indium gallium arsenide and topped it with a 5 mm long semiconductor waveguide. Measuring the output with a fast photodetector, they recorded a train of dark pulses, each of which was 90 × 10–12 s (90 ps) wide and just 30% of the normal intensity.

“Mode-locked lasers, – that is, pulses of light on zero background – have been along for quite a while now and have very wide applications, both in science and technology,” says Andy Weiner, a researcher at Purdue University, US, who has done previous work on dark soliton lasers. “So there is some intrinsic interest if you discover a different operation mode for a mode-locked laser, such as dark pulse mode as in this paper.”

Will it catch on?

Mirin suggests that his group’s dark pulse laser could find applications in telecommunications, because the dark pulses are less prone to disperse than regular, bright pulses. But Weiner thinks it is unlikely to catch on. “Current practice and directions in lightwave communications are such that I don’t think it likely there will be practical interest in dark pulse lightwave communication systems.”

The research is published in Optics Express.

Stretched molecule puts a new spin on electrons

Physicists in the US have invented a way of measuring the magnetic properties of a single molecule as it is being stretched. The technique provides a new approach for studying quantum chemistry and how the spin of an electron affects its passage through tiny structures. The technique could one day even be adapted for use in spintronic devices, which use the spin of the electron to process and store information.

The technique explores an effect first explained in 1964 by the Japanese physicist Jun Kondo. He showed that, at very low temperatures, a conduction electron in a metal such as gold can pair up with an electron of opposite spin associated with a magnetic impurity (such as iron). This tie-up curtails the electron’s ability to conduct current, resulting in a drop in the conductivity of the metal in these chilly conditions.

Physicists have observed this low-temperature fall in conductivity – known as the “Kondo effect” – in a number of bulk materials. However, something very different can happen when electrons confront just a single magnetic impurity, such as a magnetic molecule or a magnetic quantum dot. Studies of electrons flowing from one metallic electrode to another via the magnetic impurity reveal a sharp peak in the conductance of the dot or molecule at zero voltage – dubbed a “Kondo resonance”.

Jumping the barrier

For non-magnetic molecules or quantum dots, conduction is governed by the repulsive electrostatic force between an electron in the metal and an electron in the molecule or dot. Any electron wishing to hop from an electrode and into a molecule or dot must overcome this barrier. In a magnetic system, however, the same pairing interaction described by Kondo lowers this barrier, allowing an electron to jump onto the molecule or dot – and then jump off the other side.

Although this effect has already been seen in dots and molecules with one magnetic electron (spin ½ systems), studying it in higher-spin systems could shed further light on how conduction electrons behave in magnetic materials. Now, a team led by Dan Ralph at Cornell University has studied a Kondo resonance for the first time in a spin 1 molecule. The researchers have also shown that the resonance can be modified by stretching the molecule along one direction.

Triplet state

In the experiment, the team used lithography to first create a gold bridge just 500 nm long and a few tens of nanometres thick and wide on a silicon substrate. A section in the middle of the bridge was removed and a single molecule, comprising one magnetic atom (cobalt) and six pyridine rings, was put in its place.

Cobalt has two magnetic electrons that arrange themselves into a triplet state – a set of three quantum states with identical energies. Both spins point in the same direction, giving cobalt a total spin of 1. When the sample was cooled to about 1.6 K, the team noticed a big drop in the electrical resistance of the molecule at zero applied voltage – the hallmark of a Kondo resonance.

Ralph and colleagues then stretched the molecule by as much as 0.08 nm by bending the silicon substrate. The Kondo resonance was seen to split into two peaks, one on either side of zero applied voltage. According to Ralph, this splitting occurs because stretching the molecule breaks the cubic symmetry of the molecule that is responsible for the triplet states all having the same energy. Instead, one state drops in energy and the size of the drop is related to the size of the splitting.

The team confirmed the magnetic nature of the splitting by repeating the experiment in an applied magnetic field. When the field was applied perpendicularly to the direction of stretch, the splitting gradually got bigger as the field strength was turned up. However, when the field was applied parallel to the stretch, the size of the splitting changed significantly as the field strength was varied. According to Ralph, this behaviour confirms that they are observing a Kondo resonance in a spin 1 molecule.

Ralph and colleagues also looked at how the conductance at zero voltage changes as the sample is warmed from 1.6 K to about 30 K. The drop in conductance was that expected for a spin 1 Kondo resonance.

‘Important experiment’

Pablo Jarillo-Herrero of the Massachusetts Institute of Technology describes the work as “an important experiment” that could lead to better quantum-chemistry calculations, which yield the spin states of a molecule. He also believes that the work could result in the development of tiny magnetic memories that store information in terms of the spin state of the molecule. The work could even lead to the development of new sources of spin-polarized electrons and switches that can turn spin currents on and off.

Ralph told physicsworld.com that the team is now trying to repeat the experiment using electrodes made from a magnetic metal rather than gold. This would allow spin-polarized electrons to be injected into the molecule – which could be an important first step towards the creation of “spintronic” devices.

A universe of particles

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Inside the science globe (credit: CERN)

By Michael Banks

If you live near or are travelling to the CERN particle-physics lab near Geneva then you may be tempted to pay a visit to the “Universe of Particles” exhibition, which begins at the lab on 1 July.

The exhibition will be housed at CERN’s Globe of Science and Innovation and will be free to enter.

The exhibition includes four main themes including “mysterious worlds” looking at the universe and its evolution and “the Large Hadron Collider” (LHC), which is all about the world’s largest accelerator at CERN, while “detecting particles” looks at the experiments at the LHC and “science without borders” is about international scientific collaborations and the spin-offs of particle-physics research.

The four zones each contain interactive games as well as audio and video “kiosks” inside “luminous spheres” that explain research done at CERN.

At certain times during the day the whole globe will become part of the exhibition and its walls will turn into a screen on which a six minute video runs recounting the history of the Big Bang.

The exhibition will run from 10 a.m. to 5 p.m. from Monday to Saturday, and being free there is really no excuse not to go.

Radioisotopes galore at RIKEN

The chart of the known nuclides has been extended significantly by physicists in Japan, who have discovered 45 new neutron-rich isotopes. The nuclei were spotted at the RIKEN laboratory by smashing a powerful beam of heavy ions into beryllium and lead targets.

The researchers say that the 45 are just a taste of what is to come, with technical improvements expected to lead to the production of thousands of new radioisotopes that should tell us more about the astrophysical processes responsible for the creation of atoms and also lead to advances in medical technology.

Radioisotopes are unstable chemical elements that have more or fewer neutrons than the stable forms of these elements. Physicists have been producing them using particle accelerators since the 1980s, but a new generation of radioactive beam facilities will hugely extend the number of known radioisotopes. Measurements of properties such as the lifetimes and masses of these nuclei will improve our understanding of the structure and origin of atomic nuclei.

Separated by BigRIPS

The $0.5bn Radioactive Isotope Beam Factory (RIBF) at the RIKEN Nishina Center for Accelerator-Based Science near Tokyo is the first such facility to start operating. It uses a series of cyclotrons to accelerate beams of nuclei of any element up to uranium and then collides these nuclei with the nuclei of beryllium or lead. Fission or fragmentation reactions lead to the production of a range of neutron-rich unstable nuclei, which are then collected, separated and analysed using a superconducting instrument known as BigRIPS.

Shortly after switching on the facility in 2007, Toshiyuki Kubo and colleagues from RIKEN and other labs around the world discovered two new isotopes of palladium using a beam of uranium-238. At that stage, however, the experiment was limited by the relatively low intensity of the beam, because more neutron-rich isotopes are harder to create and require a much greater collision rate. By fine-tuning the cyclotrons, the Nishina Center’s accelerator team was able to increase the intensity by a factor of 50, leading to a second experiment carried out over four days in November 2008.

For the last year and a half Kubo and co-workers have been carefully analysing the collision data from that experiment, sifting out the few events attributable to new exotic nuclei from the far larger numbers of more ordinary nuclei that were produced. Among the 45 new radioisotopes that they identified were palladium-128, which is of interest because it plays an important role in the astrophysical creation of chemical elements heavier than iron and because it has a “magic” number of neutrons (82), rendering it more stable than nuclei with slightly more or fewer neutrons. Likewise, nickel-79, which was also discovered, has a neutron number of 51, putting it just one above the neutron magic number of 50 and making it an important isotope for tests of the nuclear shell model.

Beam intensity boost needed

Similar heavy-ion facilities are also being developed in Europe and the US – the FAIR project at the GSI lab in Darmstadt, Germany, and the FRIB at Michigan State University. But these machines will not be completed for several years and so for the moment will leave the field open to the RIBF (even if FAIR, when it does start up, will probe a broader range of physics, including atomic physics, plasma physics and hadron physics). “The big advantage the Japanese have is that the machine is there now,” says Bill Gelletly, a nuclear physicist at the University of Surrey. “The drawback is that they are quite slow to get the beam intensities up to the advertised levels. This limits the experiments.”

Kubo acknowledges that he and his colleagues “have just started the research process”. He says that the next step is to measure the lifetimes (expected to be of the order of a few tenths or hundredths of a second), decay properties, reactions and masses of the newly-created isotopes as well as discovering vast numbers of other new species. In addition to improving our understanding of nuclear physics, astrophysics and materials science, Kubo points out that the development of the new accelerators, targets and ion sources will lead to improvements in the production of radioisotopes for medical use and should, he says, also enhance cancer therapy using ion beams.

The work is described in arXiv: 1006.0305.

Physicists receive Knight Bachelor and DBE

By Hamish Johnston

Apologies to Colin Humphreys and Julia Goodfellow, whose names I missed when I scanned the honours list on Saturday.

Humphreys, who is director of research, Department of Materials Science and Metallurgy, University of Cambridge is to become a Knight Bachelor, for his “services to science”.

Goodfellow is vice-chancellor of the University of Surrey and will become a Dame Commander of the British Empire (DBE) for her “services to science”. Goodfellow is a biophysicist who uses computational methods to study large biologically important molecules.

Physics trio bags birthday honours

By Hamish Johnston

Oldham’s answer to Carl Sagan, the particle physicist and TV presenter Brian Cox, will be made an Officer of the British Empire (OBE) by Britain’s Queen Elizabeth II.

Cox, who is professor of physics at Manchester University, shot to fame over the past few years as a presenter of television and radio programmes about science.

Cited for her “services to physics”, Cambridge physicist Athene Donald will become a Dame Commander of the British Empire (DBE). A polymer physicist, one of Donald’s lesser known achievements is getting Physics World editor Matin Durrani through his PhD.

Also named today in the Queen’s Birthday Honours list is IOP Publishing’s managing director Jerry Cowhig, who will be made Member of the British Empire (MBE).

Cowhig has been managing director of IOP Publishing for 15 years, presiding over a major expansion of the firm’s international activities.

Both Cox and Cowhig are honoured for their “services to science”.

You can see the full list of honours here.

AFM tip ‘writes’ graphene nanowires

A simple one-step process to create nanometre-sized circuits from graphene has been developed by researchers in the US and France. The new technique involves “writing” electrically conducting nanowires onto graphene oxide using a tiny heated tip and could be ideal for making flexible electronic devices.

Graphene is a honeycomb-like sheet of carbon just one atom thick with a number of unique physical properties. Because of these properties, many researchers believe that graphene could replace silicon as the electronic material of the future. For example, it could be used to make ultrafast transistors because electrons move through it at extremely high speeds.

Single sheets of graphene are also transparent to light, a property that could be exploited to make displays, touch-sensitive screens and solar cells. Graphene could allow for lower-cost components and greater screen flexibility than current materials.

But for graphene-based technologies to be commercially viable, researchers must first develop technologies to create graphene circuits on a large scale using reproducible and reliable techniques. For example, existing methods “cut” nanowires out from a sheet of graphene and re-assemble them to make circuits.

Thermochemical nanolithography

But things may be a lot simpler where graphene is concerned. Paul Sheehan of the Naval Research Laboratory in Washington, Elisa Riedo at Georgia Tech and colleagues have now exploited the fact that graphene oxide, which is an insulator, converts back to conducting graphene when heated. However, instead of heating the entire sample, the researchers used a hot atomic force microscope (AFM) tip to convert very narrow ribbons, measuring just 12 nm across, into reduced graphene.

The technique is precise, which means that the rest of the graphene oxide sample remains insulating. Writing with different tip temperatures, from 130 °C upwards, also allows the electronic properties of the nanowires to be tuned over four orders of magnitude, making the wires more or less conducting.

“The beauty of our technique is that we have devised a simple, robust and reproducible technique that enables us to change an insulating sample into a conducting nanowire,” said Sheehan, who heads the Surface Nanoscience and Technology Center at the NRL. “The flexibility of the technique also allows the nanowires to be written before or after transfer of the graphene to a receiving material,” he told our sister website nanotechweb.

‘Very promising’

“The process – called thermochemical nanolithography – of changing the chemistry of a material with a hot nanotip is very promising and we are able to write semiconducting or metal lines in an insulating matrix by using an array of tips heated at different temperatures,” added Riedo.

According to the team, which includes researchers from the University of Illinois and the Institut Néel in Grenoble, the nanowires conduct better than doped amorphous silicon and compare well to most doped polymer conductors. However, unlike these other materials, all of the conduction occurs in a single layer of atoms in the sample.

While the research is still in its early days, it is possible that the new technique could be extended so that arrays of AFM tips rapidly write circuits at high rates across graphene wafers. Graphene could be a sort of nanoscale “electronic breadboard”, says Sheehan.

‘Rich and surprising field’

“Graphene and chemically modified graphenes, like graphene oxide, are exceptionally promising materials,” he added. “So much is known about carbon chemistry and so much has been learnt recently about carbon nanotubes that yet has to be applied to graphene. I think this will be rich and surprising field for a while to come.”

The researchers are now extending their work to single graphene sheets that have been transferred onto silicon wafers.

The results are described in Science.

Sharks hunt via Lévy flights

They were menacing enough before, but how would you feel if you knew sharks were employing advanced mathematical concepts in their hunt for the kill? Well, this is the case, according to new research, which has tracked the movement of these marine predators along with a number of other species as they foraged for prey in the Pacific and Atlantic oceans. The results showed that these animals hunt for food by alternating between Brownian motion and Lévy flights, depending on the scarcity of prey.

Lévy flight is a special class of movement characterized by many small steps punctuated by longer relocations. As the patterns show little invariance over a range of different scales, the processes associated with these movements are closely linked with fractal geometry. For instance, it has been suggested that the colourful squiggles that characterize the work of Jackson Pollock, the celebrated abstract painter, were created as his brush took a number of Lévy flights.

For the past decade, several biologists have been claiming that certain animals may also be using Lévy flights to maximize their chances of encountering prey when there is not much choice on offer. The suggestion is that they revert to this from the more random, Brownian, motion that they follow when prey is available in abundance. This hypothesis, however, has never been tested on wild animals, and it is difficult to separate the movement of animals into its different phases, which also include resting and migration.

Over 12 million movements

In new research, David Sims at the Marine Biological Association Laboratory in Plymouth, UK, working with colleagues in Europe and the US, has carried out the first large-scale survey to track the movement of foraging marine predators. Sims’ team attached electronic tags to animals from 14 different species including silky sharks (Carcharhinus falciformis) and yellowfin tuna (Thunnus albacares). 55 individuals were tracked over 12 million movements in the north-east Atlantic and the eastern and northern Pacific.

By analysing the results as a time series, the researchers were able to break down the results into sections that showed more consistent behaviour than the whole. They found that found that the sharks, tuna, billfish and ocean sunfish showed movement patterns well approximated by a Lévy walk, but that they also showed Brownian-type motion. Closer analysis revealed that individuals were switching between Lévy and Brownian movements, consistent with the idea that predators adjust their movement depending on the abundance of prey.

“We used the most reliable and robust statistical analyses on the largest data set yet analysed in this way,” Sims told physicsworld.com.

Managing stocks more effectively

“The results show that to a certain degree the movements of animals are predictable in relation to habitat types they encounter. In the case of fish, we think this will help parameterize a new wave of spatially structured population models that will help us to manage stocks more effectively in the face of overfishing and climate change, for example,” says Sims.

But despite the scale of the research, not all researchers are convinced that the research provides a particularly complete picture of marine foraging. “In this study predators are considered as fully stupid, unable to process environmental information and to act accordingly,” says Simon Benhamou, a marine ecologist at the Center for Functional and Evolutionary Ecology in France. Benhamou feels that future studies should take a more integrated approach including neuroscience, ethology and behavioural ecology.

Sims and his team intend to develop their research by tracking the foraging paths of other marine species, lower down the food chain, including octopuses and marine snails.

This research is published in Nature.

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