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Home » Page 1319

Extraterrestrial life could be extremely rare

Just because life emerged early on Earth does not mean that this is likely to occur on other Earth-like planets, says a pair of US astrophysicists. The researchers’ new mathematical model says that life could just as easily be rare – putting a damper on the excitement surrounding the recent discovery of Earth-like planets orbiting stars other than the Sun.

Estimates of the prevalence of life in the universe suffer from a severe lack of data. Indeed, they only have one data point – Earth – to support them. We are not even certain about whether our nearest neighbour, Mars, ever hosted colonies of microbes. Still, going on the Earth alone, it appears that life arose within a few hundred million years after the seething magma settled into a habitable planet. That seems early, considering that life then evolved for something like 3.8 billion years and looks likely to continue until the Sun balloons into a red giant about around five billion years from now.

“The rapid appearance of life on Earth is probably the best data we have to constrain the probability of life existing elsewhere in the universe, so it deserves to be squeezed as much as possible,” says Charley Lineweaver, an astrophysicist at the Australian National University.

Built-in ignorance

Scientists take this one piece of information from the Earth and try to say something about the probability that living organisms will appear elsewhere in a certain amount of time, provided that conditions are favourable. Previous models did not explicitly consider the effect of researchers’ prior beliefs on the outcome of these statistical studies. For example, some previous work tried to express ignorance by giving equal weight to every rate at which life could arise. But David Spiegel and Edwin Turner of Princeton University in New Jersey have now shown that this assumption actually dictates the outcome of the analysis.

They used a Bayesian method to reveal the effect of data on models that predict the probability that life arises. The theorem, developed by the 18th-century mathematician Thomas Bayes, combines a theoretical model with “prior” assumptions and data in order to draw conclusions about the probability of certain outcomes.

Because of our ignorance about what conditions are important to spark life, Spiegel and Turner modelled its origin as a “black box”. The probability that life arose on a given planet is represented by a Poisson distribution – the same type used to describe radioactive decay – and it depends on the constant probability per unit time that life will arise, and for how long life has had the opportunity to get started.

Thinking about biases

Without at least 3.8 billion years for evolution, humans would not have been around to pose the question of whether life is common in the universe. This biases sentient creatures such as humans towards existing on a planet where life started earlier. The researchers expressed this in the probability that life emerges, adding a dependence on the longest possible delay, that still leaves enough time for humans to appear, between the beginning of habitability and the advent of life.

The key to the prior term in the Bayesian analysis is the rate at which life arises. Giving each rate an equal probability in the prior, the model concluded that life is likely to emerge even without considering the Earth’s data. Conversely, by giving each possible delay period between the habitability of a planet and the onset of life the same probability, the model concluded that life rarely arose. Although both priors seem to represent ignorance, they determine the outcome of the calculation, say the researchers. Indeed, the priors build in an unwanted scale, making large rates – or large delay periods – seem more likely.

To get rid of the scale problem, Spiegel and Turner instead gave the logarithm of each rate an equal probability, and they found that the model was much more responsive to data. They considered a variety of possible scenarios for the Earth. For instance, life could have appeared 10 million years after the planet first became habitable, or 800 million years later. If life emerged in less than about 200 million years, then it seems more likely that the rate at which life arises is high. In general, however, the pair’s analysis suggests that life is “arbitrarily rare in the universe”.

Better fossil data needed

Lineweaver calls the work an “important advance”, agreeing that giving all emergence rates an equal probability is “probably too prescriptive on the result”. Still, he believes that the approach would benefit from a more sophisticated prior and alternative data. “The result is very sensitive to exactly how rapidly life formed on Earth once it could,” he says. He notes that the sparse fossil record gives only the latest limit for when life arose, not an estimate of when life emerged.

Searches for biomarkers, chemicals only known to be produced by living things, in the atmospheres of planets around distant suns could provide more data for these analyses. “The abundance of life in the universe is one of greatest questions of our time,” says Don Brownlee, an astrophysicist at the University of Washington in Seattle. “People have probably always pondered this question, but at the present time we actually have tools in hand to gain great insight into its answer.”

This research has been submitted to Proceedings of the National Academy of Sciences USA and a preprint is available at arXiv:1107.3835.

Starry Starry Night

NGC5394 and NGC5395.jpg



By Tushna Commissariat

It is commonly thought that astronomy and astrophotography are rather exclusive hobbies and that you require a lot of specialist equipment and training to pursue them. But an amateur astrophotographer, using only his ordinary digital SLR camera, a tripod and his love for the skies, has won the major astrophotography prize at the inaugural STARMUS festival.

Not only did Alex Cherney win the opportunity to attend and mingle with the who’s who of astronomy at the STARMUS festival – an astronomy and space-science festival held in the Canary Islands this June – but the Australian amateur astronomer also won an hour using one of the largest optical telescope on the planet – the 10.4 m Gran Telescopio Canarias (GranTeCan), in the Canary Islands in Spain.

Cherney’s prize-winning collection of time-lapse sequences of the Milky Way, seen over the Southern Ocean, beat a bevy of global participants for the best entry as judges felt his scenes were “chosen with the eye of an artist” and that his “subtle panning and excellent control of colour and contrast revealed technical skills of the highest order”. Cherney uses only his Nikon D700 DSLR camera and produced a compilation of images taken over 31 hours of exposure time.

This is notably the first time an amateur astronomer has been allowed access to the GranTeCan and Cherney was keen to make the most of the opportunity. After much deliberation, he decided to use his hour to observe and photograph Arp84, a pair of interacting galaxies – NGC5394 and NGC5395. (Image above courtesy: Alex Cherney)

“I wanted an object that would look nice given the parameters of the telescope and has not been photographed in colour and great detail by a professional telescope,” he said. Noel Carboni, an astro-image-processing expert, met Cherney at the festival and helped to produce a colour image. Carboni feels this is the clearest image of Arp84 ever made. Cherney felt the experience of using the telescope was “incredible”, akin to taking a space flight. “It is very hard to describe what it is like to observe space with an instrument that is helping scientists seek answers to the origin of the universe.”

Cherney put his opportunity of being at the La Palma observatory to good use, producing another time-lapse video featuring GranTeCan and MAGIC (Major Atmospheric Gamma-ray Imaging Cherenkov Telescopes) as the backdrop for the night skies. Take a look at the stunning video below.

Funding shortfall hits European X-ray laser facility

The €1.08bn European X-ray Free Electron Laser (European XFEL), which is being built at the DESY lab in Hamburg, Germany, has been left with a €150m funding shortfall after a number of member countries reduced their contributions to its construction. The Russian government has subsequently pledged to plug that gap with €50m, with Germany expected to foot the bill for most of the remaining €100m.

The European XFEL is expected to be complete by 2014, with the first users on site a year later. The 3.4 km-long underground facility will produce X-rays with wavelengths as short as 0.1 nm by accelerating bunches of electrons in a 2.1 km linear accelerator to 17.5 GeV. The facility will generate X-ray beams 30,000 times per second, with each pulse lasting less than 100 fs (10–13 s), which will allow researchers to create “movies” of processes such as chemical bonding and vibrational energy flow across materials.

Difficult economic conditions

The German government is providing most – about 54% – of the funding for the European XFEL, with 23% coming from Russia and the rest coming from 12 international partners including France, Hungary and Spain. However, the facility has recently been hit by a number of funding problems. In late 2009 the UK’s Science and Technology Facilities Council announced that the country was pulling out of the project, leaving a €30m hole in its wake (about 2.8% of the total cost). Spain and Italy have also had to reduce their contributions because of difficult economic conditions, while other issues such as boring of the underground tunnels, which is now about 70% complete, have cost more than anticipated.

The €150m shortfall has now been partly plugged by the Russian science ministry, which has pledged an additional €50m, taking Russia’s total contribution to about €300m. “Participation in mega-science projects such as European XFEL is of extreme importance to Russian scientists,” says Gennady Kulipanov, deputy director of the Institute of Nuclear Physics in Novosibirsk, Russia. “European XFEL will allow researchers to work at the bleeding edge of modern science.”

Who will fund the remaining €100m has not yet been announced officially. However, Beatrix Vierkorn-Rudolph from the German Research Ministry, who represents the country on the European XFEL’s council, says that Germany is likely to fund most of the €100m with other countries asked to make a contribution to the shortfall.

Success at SLAC

Massimo Altarelli, chairman of European XFEL’s management board, adds that the budget shortfall has not yet had an impact on the construction of the facility. Indeed, because of the success of the Linac Coherent Light Source (LCLS) based at the SLAC National Accelerator Laboratory in the US, which switched on at the end of 2009, DESY researchers have been able to improve the design of the European XFEL to produce X-rays with a wavelength as short as 0.04 nm.

“The LCLS has shown us there are more possibilities so we wanted to increase our wavelength range,” Altarelli told physicsworld.com. “Reducing the wavelength will greatly increase the resolution we can achieve.”

Do the media cover science impartially?

By James Dacey

A recently published review of the BBC’s science coverage concluded that, for the large part, its content is accurate and impartial. The review, published by the BBC Trust, consisted of an independent report from geneticist and popular-science author Steve Jones and a content analysis carried out by Imperial College London.

“[The BBC] is widely praised for its breadth and depth, its professionalism, and its clear, accurate and impartial manner,” writes Jones. “Science is well embedded into programming, on a diversity of platforms.”

Jones does, however, warn of instances where scientific debates have been misrepresented in an attempt to create balance or conflict. “Equality of voice calls for a match of scientists not with politicians or activists, but with those qualified to take a knowledgeable, albeit perhaps divergent, view of research,” Jones asserts.”Attempts to give a place to anyone, however unqualified, who claims interest can make for false balance: to give free publicity to marginal opinions and not to impartiality but its opposite.”

hands smll.jpg

But, while Jones’ report refers exclusively to the BBC, I am sure that similar conclusions could apply to other sections of the media. We want to know your opinion on this issue. On the whole, how do you find the media’s coverage of science? Please visit our Facebook page where you can take part in a poll. If you can participate, I would also encourage you to add a comment to tell us which topics you feel are covered particularly well, or particularly badly.

Earth's silent hitchhiker seen at last

Artist image of the first Earth Trojan asteroid
This artist’s concept illustrates the first known Earth Trojan asteroid (Credit: Paul Wiegert, University of Western Ontario, Canada)

By Tushna Commissarat

Looks as if the Earth has a cohort – one that has been hitching a ride with our planet’s orbit for a while now. Astronomers sifting through data from NASA’s Wide-field Infrared Survey Explorer (WISE) mission have discovered the first known “Trojan” asteroid orbiting the Sun along with the Earth. It has been known since 1772 that stable small bodies can share the same orbit with a planet or a moon – as long as they remain at stable points in front of or behind the main body. Such Trojan asteroids have been found orbiting Jupiter, Mars, two of Saturn’s moons and Neptune, but had not been seen for the Earth until now. This is because they are difficult to detect, being relatively small and appearing near the Sun from the Earth’s point of view.

Trojans circle around “Lagrange points” – gravity wells where small objects can be relatively stable compared with two larger objects, in this case the Sun and the Earth. The points that the Earth’s Trojan – called 2010 TK7 – orbits around are known as the L4 and L5 points, and are 60° in front of and behind the Earth, respectively. As they constantly lead or follow in the same orbit as the planet, they can never collide with it; so you can breathe a sigh of relief if you were worried about a possible armageddon.

“These asteroids dwell mostly in the daylight, making them very hard to see,” says Martin Connors of Athabasca University, Canada, lead author of a paper about the discovery published in Nature. “But we finally found one, because the object has an unusual orbit that takes it farther away from the Sun than is typical for Trojans. WISE was a game-changer, giving us a point of view difficult to have at the Earth’s surface.”

The WISE telescope scanned the entire sky in the infrared from January 2010 to February this year. The researchers began looking for data for an Earth-bound Trojan using data from NEOWISE – a WISE mission that focused in part on near-Earth objects (NEOs), such as asteroids and comets. NEOs are bodies that pass within 45 million kilometres of Earth’s path around the Sun. The NEOWISE project observed more than 155,000 asteroids in the main belt between Mars and Jupiter, and more than 500 NEOs, discovering 132 that were previously unknown. The team found two Trojan candidates – of these, 2010 TK7 was confirmed as an Earth Trojan after follow-up observations were made using the Canada–France–Hawaii Telescope in Hawaii.

2010 TK7 is roughly 300 metres in diameter, at a distance of about 80 million kilometres from Earth. It has an unusual orbit that traces a complex motion near the Lagrange points in the plane of the Earth’s orbit, although it also moves above and below the plane. The asteroid’s orbit is well defined and remains stable for at least 10,000 years. For the next 100 years, it will not come closer to the Earth than 24 million kilometres (by angela). An animation, with a Star Wars worthy soundtrack, showing the orbit can be found below. (Image and video credit: Paul Wiegert, University of Western Ontario, Canada.)

A handful of other asteroids also have orbits similar to Earth. Such objects could make excellent candidates for future robotic or human exploration. Unfortunately, asteroid 2010 TK7 has not been deemed worthy of exploration because it travels too far above and below the plane of Earth’s orbit, and so would require a large amount of fuel to reach it.

Elusive Sun waves come into focus

A new study sheds fresh light on the Sun, potentially explaining how vast amounts of energy are transferred from its surface to its outer atmosphere, the corona. The findings could also help to explain the origins of the solar wind, which bombards the rest of the solar system with streams of charged particles.

The corona is a region of ionized gas that extends millions of kilometres from the surface of the Sun into space. Physicists have known for more than half a century that it has a temperature of several million kelvin, while the solar surface is a relatively mild 6000 K. This surprising feature of the Sun has challenged astrophysicists, who are yet to observe directly the mechanism by which the corona is heated.

One favoured candidate for coronal heating is a phenomenon known as Alfvénic waves. These torsional transverse magnetic oscillations are believed to propagate at very high speeds. They pass along the magnetic field lines that run out of the surface of the Sun and into the corona. The phenomenon was proposed by Hannes Alfvén who won the 1970 Nobel Prize for Physics for his pioneering work on magnetohydrodynamics.

Difficult to spot

But Alfvénic waves have proved very difficult to observe. It was not until 2007 that data from Japan’s Hinode mission led to the first detection of Alfvénic waves in the corona. However, the waves that were observed were sporadic and not of sufficient energy to account for the coronal heating.

Now, four years later, a group of researchers based in the US and Europe is reporting that it has finally seen an abundance of Alfvénic waves in the corona. The new results emerged from the analysis of images collected by NASA’s Solar Dynamics Observatory (SDO), which was launched in 2007. The research team, led by Scott McIntosh of the National Center for Atmospheric Research in Boulder, Colorado, used the Atmospheric Imaging Assembly (AIA) aboard the SDO.

Black and white image of active region in the solar corona
Examining Alfvénic motion

McIntosh’s team was looking for fluctuations in features known as “spicules”, which are short-lived jets of hot gas that shoot into the corona at more than 100,000 km per hour from the chromosphere below. The researchers spotted waves at extreme ultraviolet (EUV) and X-ray wavelengths that are more than 100 times more intense than those previously measured. This, the researchers claim, is enough to heat the Sun’s outer atmosphere by millions of degrees and drive the solar wind.

Like “twanging a string”

“I would describe an Alfvén wave as simply the twanging of a string, where the motion of the gas provides the tweak and the magnetic field line is the string,” McIntosh told physicsworld.com. He said that the “incredible” spatial and temporal resolutions of the AIA instrument have enabled his group to make this breakthrough now.

McIntosh, who was involved in both the 2007 study and the recent work, will now develop the research by considering how these Alfvénic waves transfer their energy to gas in the corona. To do this, his group will need to develop computer models that are detailed enough to capture the interactions between waves and spicules.

Peter Cargill, a space and atmospheric physics researcher at Imperial College, London, welcomes the new results. “Potentially, this is a huge change into how researchers tackle the heating of the corona,” he says. Cargill believes that models will need to consider how Alfvénic waves are damped within the corona. “That needs people to get away from simple models and deal with the complexity that you see in every movie of the corona from SDO,” he adds.

This latest research is described in a paper in this week’s Nature.

Beyond the eureka moment

Scientists who invent something practical face an immediate dilemma: should they continue their research, or try to commercialize their invention? Although it is very satisfying to see an invention become a commercial success (and the monetary rewards are also nice!), this process usually takes a long time and much perseverance. Continuing research is often more fun, and may even lead to more inventions.

Yet academic scientists cannot ignore the commercial implications of their research altogether. The image of academic research as an “ivory tower” activity is currently undergoing rapid and not always voluntary changes, as universities increasingly judge scientists by the amount of funds they bring in via external contracts. Furthermore, such external financing – from government agencies as well as industrial sponsors – has penetrated academia to such a degree that if it suddenly dried up, university research would in some cases come to a grinding halt. So, rather than complaining about commercialization, individual scientist-inventors should focus on turning inventions into a rewarding part of their careers.

Novel, profitable, owned by you

If you decide to pursue commercialization, the first thing to consider is whether your invention is novel – and by novel, I mean “patentable”. The patenting process allows you to eliminate competitors for a while, giving you the freedom and time to perfect your invention without somebody stepping on your toes. Although official confirmation of your invention’s novelty must come from the relevant Patent Office authority, it is perfectly possible to do the initial estimation yourself. Open-access databases such as those on the websites of Google Patent, the US Patent Office and the European Patent Office (see links below) are all good choices for an initial search for “prior art”, which is any public disclosure of material (especially patents) relevant to your invention. However, my overall impression is that performing a patent search is a kind of witchcraft that requires the searcher to combine logical steps with the stardust of intuition. It is definitely an art, not a science and, like any art, it takes time to master.

The next question is whether your invention could turn a profit. This is a complicated question with many unknown parameters, and practical schemes for addressing it fill an entire chapter of a new book on patents that I have edited (Intellectual Property in Academia: a Practical Guide for Scientists and Engineers, CRS Press). But the short answer is that if your valuation shows that your estimated total income from your invention is less than about $100 000, then it is not reasonable to bother with patenting and commercialization.

Once you have decided that your invention is novel and profitable, the next step is to clarify whether you actually own it. For university employees, the answer can probably be found in your employment agreement (for students, it is a little more complicated – see box). Typically, these agreements state that the university owns all inventions that were made in the course of your “job for hire” (meaning that inventing is considered part of your duties), and also any inventions that were developed using university facilities. However, in certain cases the agreement may also include “everything you invent during the time of employment”. For example, if you are a theoretical physicist but you invent a mechanical component that improves the operation of your garden hose, then it is possible that the university could still own your invention. Obviously, it is important to read the intellectual property (IP) section of your employment agreement carefully.

Invention ownership may be negotiable. For example, if your university is not interested in pursuing patent protection for your innovation, it may release it and give all rights to you. Alternatively, you may be able to negotiate joint ownership of your invention. Under US law, joint ownership means that each owner possesses 100% of the invention and may do as they wish with the patent without asking another owner and without sharing the profit if the patent is sold or licensed. Under UK and EU law, in contrast, such actions are subject to consent by all co-owners.

Possible pitfalls

Commercialization is a team effort, with contributions required from not just the inventor, but legal and business professionals and university officials too. Working with such a team can have some pitfalls. One possible problem is that universities have limited funding for patenting inventions, and unfortunately most research grants do not allow recipients to spend grant funds on patenting. A change here in practice or legislation would be very beneficial, because universities would be less reluctant to patent inventions if at least some of the money required came out of scientist-inventors’ grants. Another pitfall is that university officials usually outsource patent work to accredited law firms. Typically, payment for this work is based on the number of billable hours the lawyers spend on the task, rather than on the outcome.

The most important obstacle to commercializing an invention, however, is the lack of expertise among would-be scientific inventors. A patent’s prospects for success depend largely on how thoroughly the patent search was performed, and how clearly the inventor formulated the difference between their invention and the prior art. Unfortunately, many scientists are not familiar with these IP issues, because science students seldom receive even basic IP education as part of their coursework.

To address this problem, many universities have set up special departments to help researchers commercialize their inventions. These Offices of Technology Transfer (OTT) can help shield academic inventors from the troubles associated with patenting and commercialization. However, this type of separation is not always beneficial. Typically, OTTs will only proceed with a patent application if the inventor brings them a potential licenser and can guarantee industry interest – but inventors are not allowed to share information about their invention with anyone before they file the patent application, because such disclosure prevents patenting. This catch-22 situation is particularly bad in Europe; the US is slightly better because of differences in patent legislation. So although OTTs can be helpful partners in the commercialization process, there is still a need for trained, well-informed scientist-inventors to facilitate the whole process.

Some pioneers in IP education include the Massachusetts Institute of Technology and Stanford University, both of which have offered undergraduate lectures and seminars on intellectual property for a number of years. Another leader has been the Inventor’s Studio at Rensselaer Polytechnic Institute, which offers an IP course where the goal is that each student should finish the class with a patented invention. Courses of this type can benefit both students and the university: for example, in 2007 at Stanford, a class of 75 students created smartphone and social-networking apps that collectively had 16 million users after just 10 weeks, generating about $1 m in advertising revenue during the term.

For more experienced researchers, some large conferences offer short courses and workshops on invention patenting and commercialization as part of their programme. For example, I co-chaired such a workshop in May at an SPIE conference on optical metrology (http://spie.org/x47301.xml). This “industry meets academia” workshop was dedicated to exchanging experiences among industrial and academic partners, and it was followed by specific courses that addressed important subjects such as intellectual property, technology evaluation, contracting and negotiation strategies. But in my view, we need many more such workshops, short courses at conferences, online courses and university classes to help scientist-inventors make the most of their discoveries.

Student inventions

Who owns student inventions is a complicated issue. On the one hand, students are generally paying for their education, so if they invent something, that invention cannot be classed as part of a “job for hire” at their university. On the other hand, student inventions are typically made with support from university staff, and such help can be crucial in an invention’s success.

Problems with ownership of student inventions have become more acute thanks to the current outburst of developing “apps” for smartphones or social-networking sites such as Facebook. These apps can be worth big money, and the legal questions that arise from them are now being debated across academia. One recent example is the case of Tony Brown, an undergraduate student at the University of Missouri (MU) who created an app that made it easier to track local apartment rentals on his iPhone. His app, called NearBuy, became a huge success, with hundreds of thousands of downloads.

So far, so good for Brown – until MU’s lawyers abruptly demanded a 25% ownership stake and two-thirds of any profits. In the end, MU officials relented, in the hope that by giving students more rights over their inventions, along with other incentives, the institution will become attractive to young entrepreneurs. However, MU’s (belatedly) enlightened attitude is more of an exception than the rule. The usual practice is that student inventions are considered part of the department’s research, and therefore belong to the university.

Useful links

www.google.com/patents
http://patft.uspto.gov
http://worldwide.espacenet.com

Spinons take the heat

An international group of researchers has measured, for the first time, the phenomenon of spin–charge separation in bulk in a solid. They also found that the material violates the empirical Wiedemann–Franz law that has held true for more than 150 years.

The Wiedemann–Franz law says that the ratio of thermal to electrical conductivity for a metal is approximately the same for different metals at the same temperature. It has been known indirectly, for some time, that 1D metals – chains just one atom thick – are very different from metals in 2D or 3D.The researchers, led by Nigel Hussey at the University of Bristol, UK, were looking to test a prediction made by physicists Charles Kane and Matthew Fisher in 1996, which suggested a violation of the Wiedemann–Franz law if electrons are confined to individual atomic chains.

On the 1D scale, the electrons split into two distinct components or quasiparticles – a “spinon” that carries the spin but not charge and a “holon” that carries charge but not spin. This effect – known as spin–charge separation – is derived from the study of Fermi liquids and Tomonaga–Luttinger liquids. The electrons in a 3D metal can be described as a Fermi liquid which includes the effects of electrostatic – or Coulomb – interactions between the electrons, but where the effects of the interaction have a negligible effect. But confining the electrons to 1D “quantum wires” gives a Tomonaga–Luttinger liquid, in which Coulomb interactions are much more important. In this case, spin–charge separation occurs, causing the spin and charge to propagate in different directions with different velocities. One of the surprising but key results of Kane and Fisher’s prediction is that the ratio of thermal to electrical conductivity can be sensitive to this spin–charge separation.

Purple haze

Hussey explains that while the unusual behaviour of spin–charge separation is expected in a purely 1D substance, in a 3D complex solid there is always residual coupling between individual chains of atoms. This is one reason why, since the 1996 prediction, it is only now that an appropriate solid – the quasi-one-dimensional Li0.9Mo6O17, known as purple bronze – has been found. Within the bulk of the purple bronze, there are metallic conducting wires or atom chains running through an insulating matrix. The coupling within the atom chains is limited to such an extent that the electrons are effectively confined to individual chains – thus creating a 1D world inside the 3D complex.

How spinons and holons react to an impurity
Spinons and fermions

The researchers measured the conductivity through the material by applying a current. “The chains are a few angstroms apart and many chains will have overlapping electronic orbitals. The coupling between chains and is weak, so electrons may only very occasionally hop across them.” explains Hussey.

The dramatic departure from the Wiedemann–Franz law occurs in purple bronze because when a holon comes across an impurity in the chain of atoms its motion is reflected – that is, it cannot navigate around or through the impurity. But the spinon can tunnel through the impurity and then continue along the chain. Because the spinons carry heat and the holons carry charge, the heat is conducted easily along the chain but charge is not. A similar effect occurs when the spinons or holons collide with each other. Both give rise to a violation of the Wiedemann–Franz law that grows with decreasing temperature. Interestingly, Hussey says that they were using the violation of the Wiedemann–Franz law in purple bronze “as a litmus test” to check the effective dimensionality of thier quasi 1D system. “We were surprised when the law was so spectacularly violated in this case.”

Dimensional Crossover

“There have been maybe a dozen reports of spin–charge separation before, but most of those are in completely 1D wires or nanowires or on the surface of bulk systems,” says Hussey. “This is arguably the first time it has been established deep inside the bulk of a 3D solid. But this crossover from an essentially 1D to a 3D state is not really understood and that is what we are looking at now.”

The researchers also found that when they placed the purple bronze in a magnetic field, it conducted heat as well as copper. “We were really surprised to see this as you would expect a 1D material to be a very poor conductor. But when placed in a magnetic field, the purple bronze conducted heat 100,000 times better than expected. We don’t really know why the heat is conducted so efficiently in a magnetic field and this is another aspect that we will be looking at,” says Hussey. He also points out that this surprising find could have potential technological applications.

Joel Moore, a physicist from the University of California, Berkeley in the US is impressed by the work. “There is growing application interest in various one-dimensional systems such as carbon nanotubes, and the results in this paper are confirmation that unusual 1D-specific effects appear even in ordinary transport phenomena. So I’d regard this as a model system that teaches us about other potentially useful systems.” he said.

Hussey and the team are now be investigating the high heat conduction effect in purple bronze, as well as looking at some organic conductors that are also bulk materials acting like 1D solids.

The research is published in Nature Communications.

Antiprotons pass latest symmetry test

AD at CERN
The Antiprotonic Decelerator at CERN (Courtesy: CERN)

By Hamish Johnston

For something that is rare in the universe, antimatter has certainly been in the news a lot lately.

The latest breakthrough involves antiprotonic helium and is published in Nature today. This exotic “atom” is formed when one electron in a helium atom is replaced with an antiproton, which is negatively charged.

For two decades physicists have known that antiprotonic helium is formed in a metastable state that sticks around for a few milliseconds before decaying. This should make it to possible to study its energy levels and measure the ratio of the antiproton mass to the electron mass. This could then be compared with the well-known proton-to-electron mass ratio to see if the proton and antiproton have different masses. Such an asymmetry goes against the Standard Model of particle physics and its discovery could help physicists understand why the universe is dominated by matter.

Now, physicists working on the Antiprotonic Decelerator at CERN have done just that. Masaki Hori of the Max Planck Institute of Quantum Optics in Garching, Germany, and an international team made laser-spectroscopy measurements and worked out the mass ratio to a remarkable degree of precision.

The experiment begins with pulses of antiprotons being injected into helium gas to create the exotic atoms. The team then fires laser pulses at the atoms to knock the antiproton from its metastable state to an unstable state, causing it to annihilate with the helium nucleus. This produces pions, which are easily detected. By varying the wavelength of the lasers to find the maximum rate of pion production, the team found the exact energy of the transition.

The big challenge for the researchers was that the atoms are moving about, which causes a Doppler broadening of the transition wavelength. Scientists get around this with normal atoms by firing two identical lasers in opposite directions at the target. The atom absorbs one photon from each beam – which is only likely to occur if the atom has no relative motion in the direction of the lasers, eliminating the Doppler broadening.

This is trickier to do with antiprotonic helium, and Hori and colleagues instead used lasers at two different frequencies to eliminate much of the Doppler broadening.

So after all that hard work, did they discover any new physics? I’m afraid not. The antiproton-to-electron mass ratio is the same as the proton-to-electron ratio to an impressive nine significant figures.

The work is described in Nature 475 484.

Magnetic Mecca is coming to London

Magnetism 1
Magnetism 1 by Ahmed Mater al Ziad. (Copyright: Trustees of the British Museum)

By Hamish Johnston

One of the world’s most famous scenes is of hundreds of thousands of hajj pilgrims circling the Ka’bah – the giant granite cube draped in black silk that is the most sacred site in Islam.

The photograph above is not of that swirling scene in Mecca, Saudi Arabia, but of a bar magnet surrounded by iron filings. While familiar to anyone who has studied magnetism at school, the picture also does a remarkable job of capturing the essence of the Ka’bah circumambulatory.

The image is called Magnetism 1 and is by the Saudi artist Ahmed Mater. You can see the photograph and other historical and modern objects associated with the pilgrimage to Mecca in an upcoming exhibition at the British Museum in London. The exhibition is called “Hajj journey to the heart of Islam” and runs from 26 January to 15 April 2012.

While Mater is not a physicist, he does have a strong connection to the sciences because he is a medical doctor. Indeed, some of his other works have a distinctly medical theme – including works based on medical X-rays.

You can see Mater working on his magnetic creations here.

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