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Home » Page 1419

Distant galaxy helped relight the universe

The discovery of a small but distant galaxy 12.8 billion light years from Earth is providing important clues about the earliest years of the universe’s life. By measuring the age of the galaxy’s stars, astronomers in Europe and the US say the galaxy began to shine when the universe was just 150–300 million years old. The work suggests that such galaxies were responsible for dispersing the atomic fog that once cloaked the cosmos, during a period in the history of the universe that astronomers know very little about.

Following the Big Bang, 13.7 billion years ago, the universe was hot and ionized. But as the universe expanded, it cooled, and 380,000 years after the Big Bang, protons joined electrons to make neutral hydrogen atoms, which block light. Then, stars and galaxies eventually arose whose radiation ionized the universe anew, allowing light to speed through space unimpeded – a time called the epoch of reionization.

Our understanding of this ancient era is very limited because the light from galaxies that were around at the time has travelled great distances and is therefore extremely faint when it reaches Earth. As a result the study of such galaxies can only offer tantalizing clues to what happened in the early universe. But now Johan Richard of the University of Lyon in France and his colleagues have spotted a distant galaxy that appears much brighter. “What makes this object very special is that we can really get a very strong signal on a very faint object,” says Richard.

Galaxy cluster boost brightness

The galaxy appears bright thanks to gravitational lensing. The galaxy happens to lie far behind a galaxy cluster in the constellation Eridanus named Abell 383. The cluster’s gravity splits the distant galaxy’s light into three images and boosts its brightness by a factor of eleven, making it much easier to study.

The galaxy’s redshift is 6.027, which means it is so distant that the universe’s expansion stretches the galaxy’s light waves by 602.7% as they travel to Earth. Thus, all of the galaxy’s visible and most of its ultraviolet light appears to us at infrared wavelengths.

To make the discovery, Richard’s team used optical and infrared data from two NASA observatories, the Hubble Space Telescope and the Spitzer Space Telescope. Because the galaxy – which we see as it was when the universe was 950 million years old – looks so bright, the astronomers easily determined the age of its stars: most are older than 640 million years old.

“That means that the galaxy formed these old stars very early – like only a couple of hundred million years after the Big Bang,” says Richard. His team estimates that the galaxy’s stars began shining between redshift 14 and 22, when the universe was just 150–300 million years old. For comparison, last October astronomers reported the farthest known galaxy, at redshift 8.6, but that redshift is uncertain.

‘Data is of excellent quality’

Richard Ellis, an astronomer at the California Institute of Technology in Pasadena who is not involved with the discovery, calls the implications exciting. “Because of the magnification, the data is of excellent quality,” he says, noting that earlier claims of old stars in distant galaxies were tentative. “It gives strength to the fact that there are old galaxies at redshift 6, and that means that these galaxies have been around for a long time. The implication is that there are many galaxies out there waiting to be discovered that are at redshifts of 10 and beyond.” The Hubble Space Telescope may find them, he says, if it takes deeper exposures.

The newly discovered galaxy is small, measuring only a few thousand light-years across, compared with the Milky Way’s diameter of 120,000 light years. Yet it’s spawning stars as fast as the Milky Way. Richard and his colleagues estimate that the mass of the galaxy’s stars is 6 billion times that of the Sun, a far cry from the Milky Way, whose stars weigh in at about a hundred billion solar masses.

Small galaxies such as this one may have cleared the fog that pervaded the early universe. Says Richard, “That’s why we’re using gravitational lensing to look for fainter objects, because if they’re very numerous, then they would have reionized the intergalactic medium.”

Richard and his colleagues have submitted their work to Monthly Notices of the Royal Astronomical Society Letters; a preprint is available on arXiv.

On the role of snail slime

snail1.jpg

By James Dacey

At first they may seem painfully slow and innocuous but give them an afternoon or so in your garden and they will have gobbled up your lilies before moving on to your prize-winning cabbages.

The way slugs and snails move around has captured the interest of researchers in Spain and the US, who are interested in how these slimy gastropods manage to effectively drag themselves through glue using just one foot.

Bioscientists already know that slugs and snails move by expanding and contracting their body in a series of muscular wave motions passing from the tail through to their head. What is less clear, however, is the role in locomotion played by the sticky mucus secreted from glands on the underside of the foot. This fluid is non-Newtonian, which basically means it does not deform in simple, predictable ways, like water for instance.

To investigate these slimy movements, Javier Rodríguez, a fluid dynamics researcher at the University of Carlos III in Madrid, working with colleagues at Stanford University and the University of California at San Diego, studied the gastropods in confined conditions. They captured a range images and other data of slugs and snails as they glided over transparent surfaces, which they then combined into 3D reconstructions.

To measure the speed of the body waves, for instance, they illuminated the snail’s foot from underneath using lights. Then to measure the vertical deformation of the body they shone a laser on the foot from a range of different angles (we’re informed it was a low-power laser so as not to harm the snails…)

Publishing their findings in the Journal of Experimental Biology, Rodríguez and co found is that the motion of slugs and snails has everything to do with the muscle movements of the slugs and snails and very little to do with the fact that the mucus is non-Newtonian.

Now, this may not sound like a particularly exciting result but it is good news for engineers who are trying to build robots that can drag themselves over surfaces in the same way as snails. The latest findings mean that machines could be rolled out in any old mucus and they would not need to fitted with personal supplies of special fluids.

One such idea, being proposed by a separate research group based in Japan, is to use the snail propulsion mechanism in biomedical applications to transport devices around the body. They envisage an endoscope being passed through the digestive system, taking advantage of the mucus film that lines the gastric tracts.

And if you have been left wondering why slugs and snails may have evolved to secrete complex non-Newtonian fluids, well it could be to serve other biological functions. “Without a doubt, it could have other uses, such as climbing walls, moving upside-down, or preserving moisture in the body when on a dry surface,” says Rodríguez.

How to build a cloud chamber at home

By Hamish Johnston

Olivia Donovan of Halifax, Nova Scotia sent us a link to this video she made about how to make a diffusion cloud chamber from simple household items.

My favourite bit is when Olivia (age 15) demonstrates how to remove a radioactive piece of americium from a smoke detector. “Try not to point it directly at you,” she advises.

The americium provides the charged particles, which are detected in the chamber when they cause droplets to condense out of a super-saturated vapour of isopropyl alcohol. The chamber is cooled using an “air duster” – a can of compressed difluoroethane – and in the video Donovan shows how a few blasts of difluoroethane can cool a thermocouple to –45 °C.

It’s a lovely little experiment, and amazing to think that it can be done at home.

Simon van der Meer: 1925–2011

Simon van der Meer, who shared the 1984 Nobel Prize for Physics with Carlo Rubbia, died on 4 March at the age of 85. The pair were awarded the prize for their roles in discovering the W and Z bosons – the particles that carry the weak force – at the Super Proton Synchrotron (SPS) at the CERN particle-physics lab near Geneva. Van der Meer pioneered the technique of “stochastic cooling”, which helped to ensure that sufficient antiprotons entered the collider to allow W and Z to be discovered.

Van der Meer was born on 24 November 1925 in the Hague, the Netherlands, before going on to study technical physics at the University of Technology in Delft. Graduating in 1952, he then joined the Philips Research Laboratory in Eindhoven, developing high-voltage equipment and electroncis for electron microsocopes. He joined CERN in 1956, where he was to spend the rest of his career before retiring in 1990.

Working under the leadership of John Adams – a future CERN director-general – Van der Meer made his name in the early 1960s developing a device known as a “horn” that could increase the intensity of neutrino beams. These devices are still used today as they allow focused beams of neutrinos to be sent through the Earth for hundreds of kilometres to huge, ultrasensitive underground detectors. Van der Meer then worked on an experiment at CERN for measuring the anomalous magnetic moment of the muon, which taught him the principles of accelerator design.

In 1967 Van der Meer started developing magnet power supplies for CERN’s accelerators, including the SPS and the Intersecting Storage Rings (ISR). It was while working on the ISR that Van der Meer developed the idea of stochastic cooling to increase the intensity of the collider’s proton beams. Although the technique was not used on the ISR, it was put to the test on the Initial Cooling Experiment, persuading Rubbia and others in 1976 to deploy it on the SPS. Van der Meer subsequently joined the SPS, where he helped to lead the Antiproton Accumulator project, which used stochastic cooling to accumulate enough antiprotrons for the collider.

The technique uses sensitive electrodes to pick up small “stochastic” electromagnetic signals that register that the average condition of a particle beam, such as its density. These stochastic signals – and hence the properties of the beam itself – can then be controlled using a high-frequency “kicker” that sends out rapidly varying electric and magnetic fields. The technique can therefore shrink the size of a beam in all three spatial dimensions, thereby boosting the collision rate. The beam is said to have been “cooled” because the particles occupy a smaller volume, just as gas molecules would in a cooled balloon.

Researchers at the SPS eventually discovered the W and Z bosons in an experimental run that began in late 1982 and continued into January 1983. Van der Meer also proposed a method known as “stochastic extraction” that was used at CERN on the Low-Energy Antiproton Ring (LEAR) and on its successor machine – the Antiproton Decelerator (AD). Physicists working in the ASACUSA collaboration recently used the AD to create a beam of antihydrogen atoms that is suitable for spectroscopic studies, for which the team shared the 2010 Physics World Breakthrough of the Year.

In a statement, current CERN boss Rolf-Dieter Heuer and the lab’s director of accelerators Steve Myers described Van der Meer as “a true giant of modern particle physics, though a gentle one [whose] contributions to accelerator science remain vital for the operation of accelerators such as the LHC today”. He was, they say, “an incredibly inventive man [who] when confronted with a problem would sink into deep reflection, rarely emerging until he had a solution”, adding that “stochastic cooling was typical of a Simon van der Meer invention: deceptively simple at first sight, but to anyone who truly understands accelerators it was nothing less than a stroke of genius”.

Speaking to physicsworld.com, Rubbia paid tribute to Van der Meer, calling him “one of the most extraordinary people” he had ever met. “He was able to make everybody feel at ease by the clarity of his thinking and his enormous kindness,” Rubbia added. “His ideas were extremely original and he was able to make everyone understand them.”

Rubbia first worked with Van der Meer at the CERN Proton Synchrotron (PS) where he invented the neutrino horn. “We were then together at the ISR, where he developed a very ingenious way to determine the beam luminosity and invented stochastic cooling, which has become a tremendous opportunity for proton–antiproton collisions. Comparable to his great competence was his legendary modesty. It has been a great honour for me to share the Nobel prize with him.”

A Nobel for communism

Zhores Ivanovich Alferov’s share of the 2000 Nobel Prize for Physics for the invention of heterotransistors was long overdue. Since their first appearance in 1967, these devices have revolutionized the handling of light signals in electronics in much the same way that the transistor had earlier revolutionized the technology of handling electric currents. The heterotransistor, or heterojunction, allowed the development of affordable miniaturized semiconductor appliances that have transformed daily life, underpinning a whole range of gadgets, including CD players, fibre-optic-cable networks, environmentally friendly LED lamps and more efficient solar cells.

But other aspects of Alferov’s career are less well known, as they run counter to widely held stereotypes. The title of Paul Josephson’s biography, Lenin’s Laureate, reflects the fact that Alferov is an outspoken communist, who at the age of 80 remains a leading member of the parliamentary opposition in Russia. Moreover, his prize-winning work took place in the Soviet Union during the 1960s – a period when, according to conventional wisdom, Soviet science lost its competitive edge in electronics after the shift from vacuum tubes to semiconductors. Computers serve as the key case in point, in the wake of decisions by Soviet ministerial commissions in 1967–1969 to abandon an original line of BESM-6 computers in favour of reverse-engineering the IBM-360 system. Yet as Alferov’s Nobel indicates, Soviet scientists played an often-overlooked role in the development of other crucial components of modern-day information technology.

Alferov’s research career started in 1953 at the Leningrad Physico-Technical Institute, where he helped to develop the first generation of Soviet semiconductor electronics. After completing his thesis in 1961, he embarked on an independent, forward-looking research programme on heterojunctions. At the time, labs in different countries were proudly getting ready to announce their first semiconductor lasers. However, these early devices were still inefficient, and they only worked at extremely low temperatures. In theory, lasers based on heterojunctions promised huge improvements, but almost everyone – including Vladimir Tuchkevich, Alferov’s academic adviser and the director of the Leningrad Institute – thought that, in practice, the chances of making suitable materials were nil. Two different semiconductors had to match not only in several electric properties, but also in their lattice structure.

Working with a small group of young colleagues and students, Alferov persisted, and in 1967 they accomplished the crucial breakthrough with the first ideal pair of semiconductors, gallium arsenide (GaAs) and aluminium gallium arsenide (AlGaAs). The following year, they built the first double-heterostructure laser, and in 1970 the team made it work continuously at room temperatures – an improvement for which we should feel thankful whenever we play or record a CD or DVD. The team’s accomplishment was recognized in the Soviet Union by the highest award – a Lenin Prize – in 1972.

Not every Nobel-prize winner garners a book-length biography, especially so quickly. Historians are notoriously slow to address recent and complex topics, and Josephson, a professor of history at Colby College, Maine, should be commended for his brave effort. He is uniquely qualified for the task, having previously researched the history of Leningrad physics and having known Alferov personally for years. But although he is unmatched in the speed of his research and writing, Josephson pays some price in occasional sloppiness, ranging from some trivial oversights to more serious inconsistency of thought. For example, Natalia Sonina, whom Alferov describes warmly as his first teacher in semiconductors, becomes “Nina” in Josephson’s translation. He reconstructs Alferov’s scientific trajectory on the basis of the Nobel lectures and various commentaries about the prize, but only cites, without seriously analysing, the original scientific papers by Alferov’s research team.

Josephson’s characterization of the Soviet academic system also follows some existing stereotypes that do not necessarily hold true. He describes as a disadvantage the fact that Soviet academic institutes often had to manufacture some basic instruments and materials in-house, rather than purchasing them as their Western counterparts were able to do. Yet this very feature apparently helped Alferov’s collaborator Dmitry Tretiakov to discover the right kind of semiconductor synthesized in the laboratory next door. Josephson often recites the mantra that the Soviet system did not respect the autonomy of researchers and pushed them too strongly towards applied results. But at least in Alferov’s case, the blame is misdirected. “The system” trusted Alferov enough to support his research despite his supervisor’s doubts. Meanwhile, in the US, Herbert Kroemer filed a patent for the double-heterostructure laser simultaneously with Alferov in 1963, but was refused support by his employer, Varian Associates in California’s Silicon Valley, as “the device could not possibly have any practical applications”. In the end, Kroemer shared half of the 2000 Nobel prize with Alferov.

For the biographical part of his narrative, Josephson relies mostly on Alferov’s own account Nauka i Obshchestvo, a collection of autobiographical essays and popular talks published in Russian in 2005. The book has also appeared in Italian but, as far as I know, it has not been translated into English – probably because of its strongly communist content. Alferov became a communist in the same manner in which others become Catholics or Baptists: by way of his family and cultural upbringing. His father, a worker and a soldier, joined the Bolshevik party in 1917 because of its anti-First World War stance. An atheist and communist internationalist, he married a Jewish girl despite protestations from their religious families. The couple named their sons Marks, after Karl Marx, and Zhores, after Jean Jaurès, a French socialist assassinated in 1914 for his opposition to the imperialist war.

The older son Marks turned 18 in 1942 and volunteered to defend his socialist homeland against fascism. After fighting heroically at Stalingrad and Kursk, he died in another major battle at Korsun, Ukraine, in 1944. To his younger brother, Marks Alferov has remained a life-long role model. Like him, Zhores joined the communist youth league, the Komsomol, and in 1965 the Communist Party. During the era of perestroika, he sympathized with the reformist line of Mikhail Gorbachev. For Alferov, communism now means primarily the defence of social welfare, public education and healthcare, and last, but not least, the revival of Russian science and hi-tech industry. As an internationalist, Alferov regards the dissolution of the Soviet Union as a terrible mistake, and the rise of post/anti-Soviet nationalism as a tragedy for its peoples.

Such views are not welcomed by today’s mainstream media, and to make them publishable, Josephson softens Alferov’s story and punctuates it with a general narrative about Soviet history and science. This narrative is not always relevant, but it is sufficiently anti-communist and thus more familiar to its intended readers. However, I think a better strategy would have been to not downplay Alferov’s communism, but to explain it as a modern variety, which has evolved about as far from its original version as modern global capitalism has from its origins in racist, slaveholding colonialism.

To do this, one needs to overcome the wishful blindness that wants to believe communism is just a thing of the past. Such blindness prevents the public from coming to terms with the continuing international persistence and popular appeal of communism, or even from admitting that if elections in post-Soviet Russia had been more democratic and fair, then communists would have won them on more than one occasion. For the foreseeable future, the prospects for a democratic transfer of power between political parties in Russia continue to be linked with the new communist movement as a key player. To comprehend this political situation, we need to start hearing, rather than turning a deaf ear to, the political voices of Alferov and his comrades.

  • See also “From heterostructures to nanostructures”, a special issue of the journal Semiconductor Science and Technology to mark Zhores Alferov’s 80th birthday. The issue is free to read online until the end of June 2011.

‘Jumping’ artificial atom is tracked in real time

Researchers in the US say they are first to watch a macroscopic “artificial atom” jumping between energy levels in real time. The new capability to continuously monitor the energy states of a superconducting quantum bit, or qubit, could help to correct errors in quantum computations, tightening the race between these solid-state systems and quantum computers based on trapped atoms.

An optimal measurement system for quantum computations must meet three tough conditions. For one, it must rarely misidentify states. Second, the measurement can’t scramble the qubit’s state, which is tricky because quantum states are easy to destroy. And finally, it must be fast – on the timescale of nanoseconds. This is essential for seeing quantum jumps, since many measurements must be made before the qubit changes state.

While these conditions were met 25 years ago for trapped atoms, Rajamani Vijay, Daniel Slichter and Irfan Siddiqi at the University of California, Berkeley are the first to score the hat trick using superconducting qubits – sometimes referred to as artificial atoms because of their discrete energy states.

The team did the experiment inside a cryogenic helium refrigerator cooled to 30 mK. The superconducting qubit is an aluminium circuit, a few hundred microns across but considered macroscopic, and the low temperatures brought out its quantum properties. As a nonlinear electrical oscillator, its energy levels were unevenly spaced. This allows the team to use microwaves at a frequency of 4.753 GHz to drive it only between its ground and first excited states – the qubit’s 0 and 1 states.

Revealing and protecting

The researchers connect the qubit to the superconducting microwave cavity, an ordinary harmonic oscillator, through small capacitors. Because of this link, the cavity’s preferred photon frequency changes based on the state of the qubit. The cavity could reveal information about the qubit while at the same time protecting it from noise.

To measure the qubit’s state, the team generates higher-frequency microwave photons and admits them, no more than about 30 at a time, into the superconducting cavity. There, the photons interact with the qubit and acquire a phase shift depending on the qubit’s state – 180° if the qubit is in its excited state, or 0° if it is in the ground state.

Now bearing the qubit’s mark, the photons reflect out of the cavity toward the amplifier. Like the qubit, the amplifier is a nonlinear oscillator, this time designed to behave classically. Its superconductivity means low noise since it loses no energy as heat.

The amplifier is finely tuned to accept a particular power, or rate of incoming photons, without changing their phase as they reflect back out. This is precisely the power it receives from a microwave source, which generated frequencies matching that of the signal photons.

Minuscule but important

However, in joining this stream of photons on the way to the amplifier, the signal photons exert a minuscule but important influence – adding a tiny bit more power if their phases haven’t been shifted, or interfering destructively and slightly reducing the power if they have. The amplifier is so carefully balanced that it senses even this small difference and reacts dramatically. If the power is not what the amplifier expects, it imposes a phase shift of up to 90° in either direction on the photons it reflects. This shift is one way if the qubit is excited and the other way if it is in its ground state.

The amplifier magnifies the original signal from a few photons to hundreds of photons, making it large enough to withstand the noise introduced by common methods for increasing a signal. It also rapidly changes the phase of the photons, speeding up detection. “The combination of low noise and speed was crucial in observing quantum jumps for the first time,” says Vijay.

The team extracts the qubit’s state every 10 nanoseconds – plenty often enough to monitor the qubit’s 320 nanosecond long excited state and notice when it jumped to the ground state. And now that close surveillance on a qubit has been achieved, the method can be set to work correcting errors in quantum computations.

Correcting errors

To do this, a piece of quantum information is stored across multiple qubits. If one of these qubits falls out of its state, the others can still maintain the shared quantum information, as long as the wayward qubit is brought back into line quickly. But up until now, there was no way to continuously monitor a superconducting qubit and catch it making the transition from one state to another.

“Superconducting quantum bits are without doubt one of the hot candidates in the ongoing race towards a full-scale quantum computer,” says Jens Koch of Northwestern University in Evanston, Illinois. He calls the new monitoring system “a key step forward”.

A paper describing the work will be published next week in Physical Review Letters and a preprint is available on arXiv.

Bilingualism key to the survival of a language

 

Physicists in Spain are challenging the idea that two languages cannot continue to exist side-by-side within a society. But while the findings may spell good news for some languages, it still leaves doubts over the long-term survival of more isolated languages such as Welsh and Quechua.

Jorge Mira Pérez, who led the research, became interested in the issue of language survival because of the situation in his own region of Galicia in north-west Spain where the population contains speakers of both Spanish and the local language, Galician. Teaming up with his colleagues at the University of Santiago de Compostela, Mira Pérez used a mathematical model to investigate whether these two languages could continue to coexist in the years to come.

Their approach built on an earlier study carried out at Cornell University in the US, which had modelled a two-language society by dividing a fixed population into two distinct language groups. In the Cornell model, speakers are free to switch between language groups driven by factors such as economic incentives, and the weaker language always dies out eventually.

Accounting for bilingualism

Mira Pérez’s team realized, however, that this model does not take account of bilingualism and the impact this could have on the stability of each language. So they have developed a more advanced model to include three distinct groups – the two monolinguists and the bilingual – where people can shift between all three groups.

In Mira Pérez’s model, the chance of each language group losing speakers is related to the “status” of each language, a parameter that takes into account the social and economic advantages of that language. It is also related to the number of speakers in each population to start with and the similarity of the languages in question.

To test against a real-world situation, the researchers compared their model with historical data for Spanish and Galician spanning the 19th century to 1975, and found that the fit was quite good. After varying the parameters with more than 400 different values, in order to span all the possible combinations of status and similarity, they concluded that it is possible for two languages to coexist indefinitely.

The key to survival

The key to survival is that two languages must be spoken by enough people to begin with and they must be sufficiently similar. “If the statuses of both languages were well balanced, a similarity of around 40% might be enough for the two languages to coexist,” says Mira Pérez . “If they were not balanced, a higher degree of similarity – above 75%, depending on the values of status – would be necessary for the weaker tongue to persist.”

The findings are good news for languages such as Galician and Catalan, spoken in autonomous communities in Spain, which have relatively steady numbers of speakers and share many similarities with Spanish, the dominant national language. It could spell bad news however, for more distinctive languages such as Quechua in South America, which is very different from Spanish and it is already being marginalized to rural communities.

Mira Pérez acknowledges that his model is based on an “ideal” society with static populations. It does not take into account of many other factors that could influence the balance between languages, including migration and the unpredictability of social dynamics.

Political factors

This is a view shared by David Crystal, a linguistics expert at Bangor University and author of the book Language Death. “They seem to be using a crude notion of lexicostatistics to define similarity, which is not a measure everyone respects, and they haven’t taken important social variables into account,” he says. Crystal also points out that political factors can also determine the fate of a language, as in the case of Welsh, which has seen a resurgence in recent years fuelled by two Language Acts and significant activism.

Andrea Baronchelli, a physicist at the Polytechnic University of Catalonia who has also developed an interest in the mathematical modelling of language, agrees that politics does mediate the number of speakers of a language. But Baronchelli argues that, so long as there is no pretension that mathematical studies of language can provide a complete picture, then they can still offer useful insights. “Simplification is however not automatically a problem. The role of modelling is in this case that of testing different hypothesis to show their consequences.”

Mira Pérez tells physicsworld.com that he would now like to develop his research by applying his model to other language pairings in different countries. He says he is particularly interested in the case of Belgium whose population speaks French and Dutch along with a number of minority languages. “It will be fascinating to see how similar French and Dutch although the geographical and political situation in Belgium is complex,” he says.

This research is described in a paper in New Journal of Physics. See this video abstract from the paper:

PAMELA data challenge cosmic-ray theory

Scientists in the European collaboration PAMELA say they have evidence that challenges the current theory of how cosmic rays are accelerated through the universe.

According to the team, the spectra of protons and helium nuclei passing through the cosmos are not only different from each other, but do not fit a simple “power law” trend thought to describe the relationship between the particles’ abundance and energy. The differences might mean physicists have to search for new explanations of cosmic-ray acceleration.

Cosmic rays are charged particles that rush through space, often at higher energies than those generated by particle accelerators on Earth. The vast majority of cosmic rays are protons and helium nuclei, and are thought to be catapulted forwards by the explosive shock waves of supernovae.

Shock waves

In this mechanism, the shockwaves should accelerate all cosmic rays in the same way, ultimately producing similar spectra that show how the abundance (flux) of the particles decreases with their speed (energy). For a long time, astrophysicists believed this relationship should be described by a simple power law, with flux starting high at low energies and then falling off as the energies get larger – at least up to around 1015 eV (106 GeV), when a “knee” in the spectra brings the flux down more rapidly.

Yet in recent years there have been hints that a single power law is not enough to describe the flux of cosmic rays before the knee. Last year, for example, the balloon-borne experiment CREAM indicated that the proton and helium spectra harden or curve upwards above 200 GeV. ATIC, another balloon experiment, also seemed to find deviations from a power law, although its results weren’t consistent on successive flights.

Now PAMELA has reinforced these findings. A collaboration among scientists in Italy, Germany, Russia and Sweden, PAMELA operates in space where there is little noise from the Earth’s atmosphere, and can detect cosmic rays with energies between 1 GeV and 1 TeV, which other experiments have been unable to do accurately. “What in the other experiments could only be considered a hypothesis, or one possible interpretation, now is a verified fact,” says Piergiogio Picozza of the University of Rome Tor Vergata, a spokesperson for PAMELA.

Different shapes

The PAMELA results reveal two important features. One is that the shape of the proton and helium spectra are different. To quantify this, the researchers fitted a power law to both spectra, and found that the slope of the fit was greater for protons than helium by about 0.1. The other feature is that, for each spectrum, the fit of a power law is generally poor. Between 30 and 230 GeV, the spectra curve downwards (“soften”), away from the fit line, while above 230 GeV they curve upwards (“harden”).

Most experts in cosmic rays contacted by physicsworld.com thought the difference in spectra between protons and helium would not be hard to explain. Mischa Malkov of the University of California in San Diego, for example, suggests that the helium nuclei and protons could just be accelerated in different shock waves. “Stronger shocks would produce harder spectra,” he says. “If the stronger shocks pick up and accelerate more helium than protons, the mixed spectrum will be harder in the helium component.”

However, the deviation of each spectrum from a single power law might prove more tricky for physicists. “The most intriguing evidence in the PAMELA data is the change in the spectral slope around [230 GeV], which breaks the age-old and solid idea that the cosmic-ray spectrum is a straight power law from 1 to around a million GeV,” says Damiano Caprioli of the Arcetri Astrophysical Observatory in Firenze, Italy.

The PAMELA collaboration itself is reluctant suggest explanations. In the meantime, astrophysicists hoping for a clearer picture will have to wait for the Alpha Magnetic Spectrometer, a cosmic-ray experiment that is expected to be fitted to the International Space Station later this year.

The research is published in Science DOI:10.1126/science.1199172.

Optical tweezers on your iPad

By Hamish Johnston

Imagine if you could reach out with your hands and grab a microscopic object – and watch as you move it about with micron precision or even spin it round. You could, for example, assemble a machine out of tiny components or poke and probe a bacterium or two.

Well, now all you need is an iPad – and a connection to a holographic optical tweezers system – thanks to a new software application created by researchers at the University of Glasgow and University of Bristol.

Holographic optical tweezers use a spatial light modulator to split and steer a laser beam so that it can be used to manipulate multiple microscopic objects in 3D.

The challenge, however, is how to interface such an instrument with a human operator.

In December I saw a fantastic lecture by Mervyn Miles of the University of Bristol that offered one solution – a custom-built “multi-touch table” with a screen that displays a live microscope image from holographic optical tweezers. If you pinch your fingers round a micron-sized glass ball, you can grab it with the tweezers and move it to another location.

Now Miles and colleagues have transferred this technology to an Apple iPad – perhaps not the cheapest electronic gadget, but much less expensive than their bespoke table.

You can watch a demonstration in the above video and read all about the iPad app in this paper in the Journal of Optics.

NASA’s Glory mission fails after take-off

 

A NASA mission to study how the Sun and aerosols in our atmosphere affect the Earth’s climate has failed shortly after take-off. Officials said that the $424m Glory satellite did not reach orbit and possibly landed near Antarctica, although this has yet to be confirmed.

The 545 kg craft took off on a Taurus rocket at 10.11 a.m. GMT from the Vandenberg Air Force Base in California after technical issues delayed the original 23 February attempt. However, six minutes into the launch NASA declared that the Taurus XL rocket malfunctioned and the “fairing” – the part of the rocket that covers the satellite on top of the rocket – had failed to separate properly so the satellite could not drift away in orbit. “We know that the fairing did not separate,” says George Diller, NASA’s launch commentator.

This is not the first time a NASA satellite has failed in this manner. In 2009 NASA’s $270m Orbiting Carbon Observatory did not properly separate from its Taurus XL rocket after launch. The probe later landed in the Pacific Ocean near Antarctica.

Glory was meant to operate at an altitude of 700 km carrying two main instruments: the Aerosol Polarimetry Sensor (APS) and the Total Irradiance Monitor (TIM). APS, operating from the visible to short-wave infrared, would have studied the distribution of small particles in the atmosphere – including their size, quantity, refractive index, and shape – and how they can influence the climate by reflecting and absorbing solar radiation.

The APS would have been the first space-based instrument to be able to identify different aerosol types, which will help researchers to distinguish the effect that natural and manmade aerosols have on the climate. The TIM instrument would have extended the three-decade-long record of the amount of solar energy striking the top of the Earth’s atmosphere. The accuracy of Glory’s TIM instrument was expected to be better than that of any other solar irradiance instruments currently in space.

Glory was to be the fifth instalment of NASA’s “A-Train”, which when complete will be a set of eight satellites that study changes in Earth’s climate system. It is unclear whether NASA will now finance a replacement for Glory as it has done with OCO, dubbed OCO-2, which will launch in 2013.

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