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Physics of food – the November 2016 issue of Physics World is now out

By Matin Durrani

If you love crisps – and frankly who doesn’t? – you’ll relish the cover feature of the latest issue of Physics World, in which features editor Louise Mayor tours the world’s biggest crisp factory at Leicester in the UK to see how physics is improving production of this yummy salty snack. The issue is now live in the Physics World app for mobile and desktop and will also be made available on physicsworld.com later this month.

Elsewhere in this special issue on physics and food, you can find out how electric fields could help to cut the fact from chocolate and discover why sound holds the key to our appreciation of what we eat.

You can also see how physicists – being masters of data-gathering, modelling and simulation – are ideally placed to develop products that are healthier, more nutritious and make more of our resources. Find out too how soft-matter physicists are crafting “functional” foods that promote feelings of fullness and satisfaction.

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Flash Physics: Thirty Meter Telescope could go to Spain, artificial muscles flex, light switches light

Canary Islands chosen as alternative site for Thirty Meter Telescope

Originally planned for Mauna Kea mountain in Hawaii, the Thirty Meter Telescope (TMT) could be built at the Observatorio del Roque de los Muchachos in the Canary Islands. The TMT International Observatory (TIO) Board of Governors has chosen the observatory in Spain as the “primary alternative” to the controversial Hawaiian site, which is being opposed by native Hawaiians who see building the TMT on Mauna Kea as a desecration of their spiritual and cultural pinnacle. Chair of the board Henry Yang says: “Mauna Kea continues to be the preferred choice for the location of the Thirty Meter Telescope, and the TIO Board will continue intensive efforts to gain approval for TMT in Hawaii.” In July 2016, TMT deputy project-manager Fengchuan Liu said that the decision to build the TMT on an alternative site will be taken “by early 2017”. Construction of the TMT is planned to begin in April 2018, with completion in 2022.

Improving the flex of artificial muscles

A new type of artificial-muscle fibre that has high tensile strength and actuates – expands or contracts in response to a stimulus – at much cooler temperatures than previous fibres, has been developed by researchers at the Louisiana State University in the US. Guoqiang Li says the team was able to exceed the performance of other artificial muscles by focusing on the thermal properties as well as the molecular structure of their polymer fibre. According to Li, the team found that two factors are crucial for high performance – the untwisting nature of the fibre during actuation and its negative coefficient of thermal expansion. “The actuation temperature is very high in the polymer fibres used previously, for example they can go to 160 °C,” says Li. “For some applications, like medical devices, [the] actuation temperature is too high. So you need to find a way to lower it.” Li’s group managed to bring the maximum actuation temperatures down to 67 °C. This lower temperature is particularly significant when considering applications related to human body temperature. In addition to medical devices, such applications include breathable textiles and self-healing materials with structures that adapt to environmental changes. The research is described in Applied Physics Letters.

Dim light controls intense laser field

Image showing the design of the non-Hermitian photonic metamaterial — Light work: design of the non-Hermitian photonic metamaterial, which was created within a silicon waveguide. (Courtesy: H Zhao *et al./Phys. Rev. Lett.*)

A new way of switching a beam of light on and off using another light beam has been unveiled by physicists in the US. Unlike other “light–light” switching schemes, which employ intense light beams to control relatively dim beams, this latest technique uses a weak beam to control a much brighter beam. The switch makes use of a new type of optical material called a non-Hermitian photonic metamaterial, which is created within a silicon optical fibre. Tiny features in the silicon create a standing wave when infrared signal light is shone into one end of the fibre. When control light is shone into the opposite end of the fibre, destructive interference in the fibre prevents the signal light from being transmitted. Created by Liang Feng at the State University of New York at Buffalo and colleagues and described in Physical Review Letters, the new switch could – with further improvements – find use in high-speed, all-optical telecoms networks of the future.

You can find all our daily Flash Physics posts in the website’s news section, as well as on Twitter and Facebook using #FlashPhysics. Tune in to physicsworld.com later today to read today’s extensive news story on neutron holograms.

Why aye, astronomer lad

There are a lot of books out there about backyard astronomy. An Astronomer’s Tale is almost certainly the only one that will, in addition to introducing the constellations and offering tips about deep-sky observing, also teach you how to split a brick in half and describe what it feels like to fight in a Sunderland–Chelsea football gang war. The author, Gary Fildes, grew up in the north-east of England in the 1970s, when most adult men in the area worked down the mines, in the Sunderland shipyards or on a building site. After a chequered career at school, young Gary chose the third option, and trained as a bricklayer. “My future was Sunderland and I would do Sunderland things whether I liked them or not,” he writes. “More times than not, I liked them back then.”

He did have an interest in astronomy, sparked by a childhood Christmas when one of his brothers received a telescope, but after being beaten up as a teenager for talking about the Moon, it was a passion he kept to himself. Then, in his mid-30s, something changed; as Fildes puts it, “I came out. As an astronomer.” He began reading science books in the evening, bought his own telescope, and started going along to meetings of the Sunderland Astronomical Society, or SAS (motto: “Who Stares Wins”). Eventually, Fildes’ passion for astronomy completely transformed his life. Today, he is lead astronomer at Kielder Observatory, home to some of the darkest skies in the whole of the UK and a major attraction for people eager to reconnect with the night sky.

In An Astronomer’s Tale, Fildes intersperses stories from his upbringing with a series of monthly guides to the night sky. The observing tips are honed by years of experience, and Fildes excels at capturing the atmosphere at public observatories and star parties, where red light bulbs “create an atmosphere of secrecy, as if we are all children hiding beneath a duvet cover”. His book also offers a gentle reminder to professional astronomers – who spend most of their time glued to computer screens rather than telescope eyepieces – not to forget the simple pleasures of observing. “Is their inspiration, their ability to dream about our universe, getting lost in the technical jungle of scientific progression?” he wonders. If it is, places like Kielder – and books like this one – will surely help them find it again.

2016 Century £16.99hb 320pp

Science under duress

Black-and-white photo of Josef Stalin in military uniform — Triumph and tragedy: A new book looks at the science and the scientists in Russia and the Soviet Union, particularly the contrasting fates of biology and physics under Stalin.

The idea that all branches of scientific knowledge will someday unite to create a single, logical explanation of the universe has been captivating scientists and philosophers for generations. In the mid-19th century, Karl Marx made this “scientism” an important thread of his materialist philosophy, and the impulse behind it is still apparent today in efforts to develop a “theory of everything” in physics. In the first half of the 20th century, however, this dream bore bitter fruit thanks to Vladimir Lenin and Josef Stalin, whose devotion to Marx’s “one science” contributed to the deaths of millions of ordinary Russians.

How this happened is the subject of Stalin and the Scientists: a History of Triumph and Tragedy. In it, author Simon Ings, a science writer and arts editor at New Scientist magazine, sets out to cover “more or less the whole of scientific life” in Russia and the Soviet Union between 1905 and 1953. For much of the book, though, the tragic story of Soviet genetics takes centre stage. As Ings explains, the theories of Charles Darwin and Gregor Mendel dictate that change takes place over many generations and heritable characteristics are passed down more or less unaltered. However, these ideas were anathema to the Bolsheviks: the revolutionaries who overthrew the Russian tsar in 1917 wanted to change society overnight, while talk of inherited qualities smacked of support for the aristocracy. Naturally, they preferred an alternative theory in which organisms change in response to their environment and pass down these changes to the next generation.

In recent years, this “Lamarckian” theory (named after the early 19th-century French scientist Jean-Baptiste Lamarck) has been partially rehabilitated by the emerging science of epigenetics. However, the version promulgated by Stalin’s favourite geneticist, the charlatan Trofim Lysenko, had nothing at all to recommend it, and its widespread application worsened the famines that struck the Soviet Union during the 1930s and 1940s. Despite this, geneticists who persisted in Mendelian views were liable to be demoted, sent to the gulag or (at the height of Stalin’s purges in the mid-1930s) shot.

In comparison, Ings notes, Soviet physicists got off lightly. Although many of them also spent time in the gulag, there was never a physics equivalent of Lysenko, and the contrasting fates of Soviet biology and Soviet physics make interesting (and sometimes troubling) reading. Covering the entirety of Soviet science is an ambitious task, but Ings tears into it with gusto, ably recounting the careers of dozens of biologists, agronomists, physicists and Communist Party officials during one of the most tumultuous periods in world history.

2016 Faber and Faber £20.00hb 528pp

New Ising-machine computers are taken for a spin

Two independent teams of physicists in the US and Japan have each built versions of a new kind of computer called an “Ising machine”. The devices use physical systems to imitate a network of interacting magnetic spins with the aim of solving very complex optimization problems. Although the full potential of these Ising machines remains to be explored, the researchers say that their initial results show that their optical-fibre-based devices work just as expected. Furthermore, the research suggests that future Ising machines could outperform conventional, digital computers when it comes to discovering new drugs or optimizing the efficiency of factory production lines.

Ising machines are designed to find the best solution to problems that involve large numbers of competing alternatives. This involves performing “combinatorial optimizations” that are “NP-hard”, which means that the number of possible solutions increases exponentially with the number of components in a system. Examples of such problems include the “travelling-salesman problem” – which involves planning the shortest route linking a number of different cities – as well as the process of finding combinations of atoms and molecules that are good candidates for potential new drugs. Even the most powerful conventional computers are simply unable to provide practical solutions to these problems.

Ising machines are named after German physicist Ernst Ising, who studied the problem of how a set of spatially distributed magnetic moments arrange themselves in their lowest-energy state, given that each moment can assume one of two values: either spin-up or spin-down. For spins strung out along a line that only interact by pointing in the opposite direction as their two nearest neighbours, the answer is trivial: it is up, down, up, down, etc. But the problem becomes extremely difficult to solve when considering more general configurations in which each spin interacts arbitrarily with every other spin. The problem then is NP-hard.

Physical systems

The idea behind an Ising machine is to “map” a difficult optimization problem on to a specific Ising problem containing spins with certain couplings, and to find a physical system that will be able to solve a wide range of such problems. As Peter McMahon of Stanford University in the US points out, an Ising machine could be made simply by arranging bar magnets at certain nodes in a 2D grid and then looking to see how the magnets end up aligning with one another. One problem, he says, is that such a device would only be able to solve one specific Ising problem, dictated by the spacing – and hence coupling – between magnets.

Scientists have already worked on a number of more sophisticated alternatives. In the 1980s, John Hopfield and David Tank carried out work on neural networks in which each artificial neuron represented a spin. The firing or not-firing states of a neuron correspond to spin-up or spin-down and the weights of neural connections represent the coupling strengths. More recently, researchers at Canadian company D-Wave and elsewhere have looked to devices known as adiabatic quantum computers. These exploit the phenomenon of quantum tunnelling to place a set of quantum bits into their lowest energy state – in analogy with the Ising model.

When we constructed our machine there was no guarantee that we would get anything useful out of it so when we turned it on we got a pleasant surprise
Peter McMahon, Stanford University

According to McMahon, both of these options suffer from the fact that each spin usually only couples to nearby neighbours. That means that although such devices can still solve arbitrary problems, they must be made much bigger to do so. Typically, he says, to solve an n-spin Ising problem they need about n² physical spins.

Light pulses

The idea for the new Ising machines came from Stanford’s Yoshihisa Yamamoto as part of the Japan Science and Technology Agency’s ImPACT programme. Yamamoto and colleagues showed in 2014 that they could build a small Ising machine by feeding a sequence of light pulses into an optical cavity. Spins were represented by pulses’ phase and were made to interact by diverting a small part of each pulse along an optical component known as a delay line, such that the pulse fragment re-entered the cavity as the next pulse passed by. But the need for many delay lines makes the approach hard to scale up and indeed the researchers only managed to process four pulses.

Now, two separate efforts, spawned from that original research, have created very similar variations on the initial device by marrying optics and electronics. Rather than sending tapped pulses along delay lines, the researchers instead measure the pulses’ phases and send that information to an electronic circuit, which adjusts the strength of a laser beam shone into the cavity in such a way as to mimic the effect of the delay lines.

Yamamoto, McMahon and colleagues at Stanford have built an Ising machine with 100 spins, each of which couples to every other spin, and have used the device to solve or find good approximate solutions to some 4000 Ising problems. Meanwhile, a group led by Hiroki Takesue of NTT Corporation near Tokyo has managed to build a machine with 2000 spins, again with complete spin–spin coupling, but in this case testing the device against just three problems.

Wireless networks

Takesue says that he and his colleagues are now testing their machine against other Ising problems and are also investigating several candidate applications, including drug discovery and the optimization of frequency channels in wireless networks. He adds that they also plan to increase the number of spins to more than 20,000 over the next three years.

McMahon is confident, on the basis of theoretical extrapolations, that the NTT machine can, like his group’s device, solve a wide range of Ising problems. But he says it is unclear whether this machine, or an even larger version of it, will outperform classical computers. “When we constructed our machine there was no guarantee that we would get anything useful out of it so when we turned it on we got a pleasant surprise,” he says. “But it remains to be seen whether this particular approach can beat state-of-the-art classical machines in real-world applications, or whether we will need a new computing architecture.”

The Ising machines are described in separate papers in Science.

Flash Physics: Detector nears the quantum limit, why Saturn has rings, monolayer emits photon pairs

New microwave detector approaches the quantum limit

A new and extremely precise way of amplifying and measuring tiny microwave signals has been unveiled by physicists at Aalto University and the University of Jyväskylä in Finland. Mika Sillanpää, Tero Heikkilä and colleagues created their detector by combining a micron-sized mechanical resonator resembling a drum with two superconducting microwave cavities. The device is able to amplify a very weak microwave signal with a gain of 41 dB – a factor of about 12,500 – while only adding about four quanta of noise to the signal. This is close to the minimum amount of noise possible (the standard quantum limit), which is half a quanta of noise. As well as being able to amplify very weak signals so that they can be measured, the technique could be used in quantum-information systems in which quantum bits of information (qubits) are encoded into microwave signals. Another important feature of the new technology is that it can convert signals from one microwave frequency to another. Writing in Physical Review X, the team suggest that this could be useful for developing quantum-information systems that are based on several different qubit technologies.

Computer simulations shed light on planetary rings

A series of computer simulations done by scientists in Japan and France provide important insights into how the rings around Saturn and other planets formed – and why the composition of Saturn’s rings is different to that of the rings of Neptune and Uranus. Ryuki Hyodo and colleagues at Kobe University, the University of Paris Diderot and the Tokyo Institute of Technology focussed on the “late heavy bombardment” era of the solar system. This happened about four-billion years ago and is thought to have involved the inward migration of thousands of Pluto-sized objects from the outer solar system. The team first calculated the probability that some of these objects would pass close enough to Jupiter, Saturn, Uranus and Neptune such that they would be broken up by tidal forces. The researchers found that enough fragments would be created and then captured by the giant planets to account for the current rings of Saturn and Uranus. Simulations also revealed that these fragments – some of which would be several kilometres in size – would break up as they orbit the planets to become the circular rings of much smaller objects seen today. The simulations offer a suggestion as to why Saturn’s rings are made mostly of ice, whereas the rings of Uranus and Neptune contain much more rock. This, they write in Icarus, is because Saturn is less dense than Uranus and Neptune and therefore the tidal forces it exerted on the Pluto-like objects is weaker. As a result, Saturn’s gravity was only able to chip away at the ice on the surface of the passing objects whilst Uranus and Neptune were able to break up the underlying rock.

Transition-metal monolayer emits photon pairs

Artist's impression of the two-photon source — Red light, green light: the monolayer of tungsten diselenide (below in this artist’s impression) emits exactly two photons of different frequencies under suitable conditions. They are depicted in red and green. (Courtesy: Karol Winkler)

A 2D monolayer of transition metal dichalcogenides (TMDC) can be used to generate pairs of photons, say researchers at the Julius-Maximilians-Universität Würzburg in Germany. TMDCs behave like semiconductors and are often used to make ultra-small and energy-efficient chips. Christian Schneider, Sven Höfling and colleagues produced monolayers of tungsten diselenide by using a piece of tape to peel off thin layers from a multi-layer film of the TMDC. This involved repeatedly peeling the film so that thinner and thinner layers are made until the material on the tape is only one-atomic-layer thick. This layer is then cooled down to a temperature just above absolute zero and it is then excited with a laser, causing it to emit single protons under specific conditions. “We were now able to show that a specific type of excitement produces not one but exactly two photons,” says Schneider. “The light particles are generated in pairs so to speak.” Two-photon sources are of interest to those carrying out quantum cryptography and other such protocols that involve entanglement. The research is described in Nature Communications.

You can find all our daily Flash Physics posts in the website’s news section, as well as on Twitter and Facebook using #FlashPhysics. Tune in to physicsworld.com later today to read today’s extensive news story on Ising machines.

Computing in a chilly Beijing

By James Dacey

Today is my first day in Beijing and boy am I glad I packed my winter coat. Despite the clear blue skies, it was just above freezing point as I arrived at the Beijing Computational Science Research Center (CSRC) this morning, with an icy wind bringing an added chill factor. I was with my IOP Publishing colleague Tom Miller as we were delivering a presentation about scientific publishing and journalism and our taxi driver decided that 2 km from the venue was as far as he fancied going. So a brisk walk later we arrived with chattering teeth in need of a thorough thaw.

Located a few kilometres north-west of Beijing’s centre, the CSRC is within the Zhongguancun hi-tech zone. The majority of buildings within the technology hub are occupied by commercial firms, and our icy walk took us past the impressive modern offices of Baidu and Lenovo among other companies. The CSRC, however, is focused primarily on the application of computational modelling to fundamental science research. Its seven divisions include physical systems, quantum physics & quantum information, and materials & energy.

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3D cosmic-microwave background, iPhone paper and Dance Your PhD winner

https://youtu.be/3GSwl21-ZwI&rel=0

By Michael Banks

It might look like a kind of dumpling at first sight, but upon closer inspection the eagle eyed might spot that it is actually a 3D version of the cosmic microwave background (CMB) – the thermal remnant of the Big Bang that came into being when the universe was only 380 000 years old. The model was created by physicist Dave Clements from Imperial College London who says that detailed maps of the CMB – created by space telescopes such as the European Space Agency’s Planck satellite – are difficult to view in 2D. (more…)

Building-block metamaterials shape 3D acoustic holograms

Researchers in the US have created a printed array of metamaterials that can produce passive 3D acoustic holograms from a simple sound source, such as a single speaker. The device is made up of 3D-printed Lego-like blocks that can be put together in different configurations. The researchers say that their method is cheaper and simpler than other techniques and that they expect it to “open a new realm of holographic acoustic wave manipulation”.

A visual hologram manipulates electromagnetic waves in the visible part of the spectrum to create a 3D image. Because sound also travels in waves, it should be possible to create complex 3D fields of sound – acoustic holograms – in a similar way. While visual holograms can be made with physical structures that diffract light, it isn’t so easy with sound due to a lack of materials with the required acoustic properties. Generally, acoustic holograms use a transducer array controlled by complex phase shifting electronics.

Shifting sound

The new device created by Steve Cummer, an electrical and computer engineer at Duke University in North Carolina, US, and colleagues uses metamaterials to create a physical structure that can shift sound waves into the required 3D shapes. Metamaterials are engineered materials that have structural properties that don’t usually occur naturally. They are used to control and manipulate light, sound and other physical phenomena.

The device is made up of a range of 12 3D-printed plastic blocks, or “cells”. Each cell contains a different labyrinth pattern that is designed to modulate the phase of an acoustic wave. They work at a frequency of 4000 Hz and the 12 cells cover 180° of relative phase delay. A double layer of the cells can produce 360° of relative phase delay.

Cummer told physicsworld.com that although printing the cells was “time consuming,” fabricating each individual piece was “straightforward”. The more challenging part, he added, “was actually designing the components so that each one manipulates sound in precisely the way we need”.

Wave patterns

The cells slot together and can be rearranged to create different wave patterns. Once built, the array is placed in front of a single speaker and the acoustic hologram is produced on the other side. The construction of the array was aided by numerical simulations that show how the cells individually affect sound waves and how they act in combination. The researchers tested two different holograms. First, they used the array to project sound in a letter “A” pattern 30 cm from the hologram. Then they rearranged it to produce three circular hot spots of sound of different diameters.

Cummer says that although the goal was to “simply demonstrate a new concept”, now they have established that it is possible they are “thinking hard about where the idea might be deployed”. One possible application is the creation of “an acoustic hologram that converts the sound from a single speaker into the much more complex sound field created by an orchestra”.

It could also potentially be used for medical imaging. The transducer arrays used in ultrasound devices allow the acoustic field to be adjusted during imaging. While the new technique does not offer this level of control, it could be used for simple imaging if “you knew the depth of the object you were trying to image”, Cummer says. Such devices would not be as capable as current ultrasound imaging systems, but they would be cheaper and “orders of magnitude less complex”.

Reconfigurable holograms

Bruce Drinkwater, professor of ultrasonics at the University of Bristol in the UK, says that “this is a really nice idea. Arrays are expensive, particularly the electronics required to drive them. This paper makes beam-forming much easier and cheaper.” Discussing its potential application for medical ultrasound, Drinkwater says that “[transducer] arrays are still the gold standard” but “if you want to perform a fixed beam-forming operation – e.g focus on a specific tumour on a specific patient – this idea is perfect.”

The device as tested does not work at ultrasound frequencies, but Cummer says that scaling it up or down to work at different frequencies “should be pretty straightforward”. “The challenge of scaling down for higher frequencies like ultrasound is simply manufacturing the components in a much smaller size. 3D manufacturing approaches are evolving very quickly, and we are working with colleagues with experience in this area to do exactly this.”

Cummer adds that they would also like to “be able to show the same kind of dynamic sound-field manipulation with a single source and reconfigurable hologram” as has been shown with transducer arrays. “We are working towards that.”

The work is published in Scientific Reports.

Flash Physics: Particle pioneers bag J J Sakurai Prize, Brian Bowsher appointed new head of STFC, colliding light waves may create magnetic monopoles

Particle-physics pioneers bag J J Sakurai Prize

The American Physical Society’s J J Sakurai Prize for Theoretical Particle Physics has been awarded to Sally Dawson of Brookhaven National Laboratory, Gordon Kane of the University of Michigan, Howard Haber of the University of California, Santa Cruz, and John Gunion of the University of California, Davis, all in the US, for “instrumental contributions to the theory of the properties, reactions, and signatures of the Higgs boson”. All four winners also authored The Higgs Hunter’s Guide, an important book first published in 1989 that detailed the physics of the then-elusive Higgs particle. “It’s a great honour to receive this award with such distinguished scientists,” says Dawson. She also highlighted the importance of theoretical work, saying that “you never would have found the Higgs if you didn’t know what you were looking for. The searches were based on years of calculations and the detectors were designed to find this thing based on that theoretical work, which is still ongoing.” The quartet will receive their award, which consists of $10,000 to be shared and certificates citing their achievements, at a ceremony next January in Washington, DC.

Brian Bowsher appointed new head of Science and Technology Facilities Council

Brian Bowsher has been appointed as the chief executive of the UK Science and Technology Facilities Council (STFC) and will take up the post from next month. Bowsher will replace current head John Womersley, who has been appointed the next director-general of the European Spallation Source research facility. Bowsher was previously the managing director of the National Physical Laboratory, for more six years. “Bowsher is a highly respected scientist, with extensive experience leading world-class science laboratories, managing major science facilities and representing the UK on an international stage,” says science-minister Jo Johnson. “As a member of the STFC Council, he is already familiar with the organization, making him the ideal person to promote the UK’s scientific expertise and extend our international collaborations.” Bowsher received his PhD in inorganic chemistry from the University of Southampton in 1981, and has published extensively on materials, chemistry and nuclear-fuel issues. “It is an honour to be asked to lead the STFC and drive scientific research with our partners, both in the UK and internationally,” says Bowsher, who was first appointed to the STFC Council in May 2013.

Could colliding light-waves create magnetic monopoles?

Magnetic monopoles may form via wave-wave collisions — Single poles: magnetic monopoles – theorized particles with only one magnetic pole – might possibly be created by wave–wave collisions. (Courtesy: Vachaspati *et al./Phys. Rev. Lett.* **117** 181601)

Ever since famous physicist Paul Dirac first predicted the existence of magnetic monopoles in 1931, physicists have looked high and low for these elusive particles. Dirac predicted the existence of a monopole as a way of explaining electric-charge quantization and finding them could help researchers to move towards unifying fundamental forces. Indeed, scientists have looked everywhere from particle accelerators to polar rocks to “spin ices” and have even tried creating them in the lab – all of the searchers in nature have ended in vain. Now, theorist Tanmay Vachaspati from Arizona State University in the US says that monopoles may form via wave collisions of force-carrying particles like photons. He calculated that it may be possible to see signatures of monopoles emerging from the collisions of two circularly polarized, high-intensity laser beams. Vachaspati’s simulations showed that monopoles formed as cratered peaks in the energy density in the wake of a head-on collision and that isolated North- or South-Pole magnetic fields formed around the peaks. The research is published in Physical Review Letters.

You can find all our daily Flash Physics posts in the website’s news section, as well as on Twitter and Facebook using #FlashPhysics. Tune in to physicsworld.com later today to read today’s extensive news story on creating acoustic holograms.

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Physics of food – the November 2016 issue of Physics World is now out

Flash Physics: Thirty Meter Telescope could go to Spain, artificial muscles flex, light switches light