Two years ago, researchers at Linköping University in Sweden showed that a rose can form the basis of a transistor. Now team member Roger Gabrielsson and colleagues have used a similar flower to create a supercapacitor that can store a large amount of electrical energy. The team put a cut rose into a polymer solution, which was absorbed by the flower. The material polymerizes spontaneously within the stem, leaves and petals of the flower to create long threads that conduct electricity. This allows a large amount of electrical change to be pumped into the flower. “We have been able to charge the rose repeatedly, for hundreds of times without any loss on the performance of the device,” explains team member Eleni Stavrinidou. “The levels of energy storage we have achieved are of the same order of magnitude as those in supercapacitors.” She adds that without any further optimization, the rose supercapacitor is capable of powering an ion pump and various types of sensors. The rose supercapacitor is described in the Proceedings of the National Academies of Science.
Head of Oak Ridge National Lab steps down
Thom Mason will leave Oak Ridge National Lab in July. (Courtesy: ORNL)
Thom Mason has announced he will step down as director of Oak Ridge National Laboratory (ORNL) on 1 July 2017 – exactly 10 years after first taking the job. ORNL is the US’s largest science and energy laboratory and focuses on materials, neutron science, energy, high-performance computing, systems biology and national security. It operates two neutron facilities – the High Flux Isotope Reactor and the $1.4bn Spallation Neutron Source – as well as two supercomputers. Mason, an experimental condensed-matter physicist originally from Canada, will become senior vice president for laboratory operations at Battelle – a private non-profit science and technology firm that is based in Columbus, Ohio. Battelle, together with the University of Tennessee, manages ORNL for the US Department of Energy. ORNL is now looking for Mason’s replacement.
Triboelectric generator gives mass spectrometer a boost
Anyin Li of Georgia Tech demonstrates the use of a sliding triboelectric nanogenerator to produce electrical charges for the mass-spectrometer device shown next to him. (Courtesy: Rob Felt/Georgia Tech)
A device that generates electricity from friction has been used to increase the sensitivity of a mass spectrometer to “unprecedented levels”, according to Facundo Fernández, Zhong Lin Wang and colleagues at the Georgia Institute of Technology in the US. Triboelectric nanogenerators (TENGs) convert mechanical energy to electrical energy and are of great interest to Wang and others who are building systems to harvest energy from the environment. The team’s TENG provides an ionizing voltage of 6000–8000 V to a mass spectrometer, compared with the 1500 V that is supplied by a conventional source. The TENG voltage alternates in polarity and the corresponding current is supplied in a very precise manner. The team believes that this voltage is extremely efficient at ionizing the sample – the first stage of operation of a mass spectrometer – and this means that a stronger measurement signal is obtained. The alternating and controlled nature of the signal also allows higher voltages to be used without damaging the sample or the mass spectrometer. Most mass spectrometers operate in a pulsed mode, so a pulsed TENG ionization voltage could be synchronized to ensure that the sample is only ionized when necessary. This could allow very small samples to be analysed at higher sensitivities because precious ions would not be wasted. Fernández says that the TENG allowed “us to reach sensitivity levels that are unheard-of – at the zeptomole scale”. TENGs could also make mass spectrometers more compact and portable by replacing conventional ionization voltage supplies, which tend to be large and bulky. Looking further into the future, it may even be possible to create mass spectrometers that are powered by TENGs alone. The research is described in Nature Nanotechnology.
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From books and lectures to blogs and social media, today’s physicists are expected to do far more public communication than their predecessors. However, communicating science well is far from easy. Obstacles include the comfortable familiarity of jargon and a natural distaste for the imprecision required by simplification. But there is a more fundamental barrier, which arises from scientists and non-scientists speaking different languages and having different mental models of how the world works.
In my career as a science communicator, I have observed countless online exchanges between scientists and the public, I’ve read and reviewed more than 1000 popular-science books, written 26 of my own, and spoken to numerous readers and attendees at public lectures. My conclusion is that physicists find communication hard because their idea of the questions physics is trying to answer is so different from those of their readers and the wider public. Although physicists aren’t unique in these problems, the concepts they need to communicate are often less immediately accessible than those from biology, chemistry and other fields.
The scientist–public language barrier was perfectly highlighted in a blog post written last September by Sabine Hossenfelder, a theoretical physicist and research fellow at the Frankfurt Institute of Advanced Studies (ow.ly/NsJO3077wZc). Hossenfelder puts a lot of effort into communication, not only through her Backreaction blog but also interacting via social media and writing for magazines, including Physics World (see “Can we unify quantum mechanics and gravity?” October 2013 pp42–43). She is anything but an ivory-tower physicist.
In her post, Hossenfelder analyses a question-and-answer discussion on Discover magazine’s website last September between staff editor Bill Andrews and a reader called Jeff Lepler from Michigan in the US. “Are we,” wonders Lepler, “any closer to understanding the root cause of gravity between objects with mass?” To which Andrews replies: “Sorry, Jeff, but scientists still don’t really know why gravity works. In a way, they’ve barely just figured out how it works.”
To the public, science is about the search for simple truths that explain how nature functions and, as a result, possibly also getting some idea of the why
In response, Hossenfelder asks “What’s that even mean – scientists don’t know ‘why’ gravity works?” She asks this rhetorically, going on explain that why gravity works is not a scientifically meaningful question; it’s rather how gravity works that physicists aim to answer.
It has only been since the development of modern science, however, that scientists have concentrated on answering how something works. In the time of natural philosophy – the precursor to modern science – scholars did indeed attempt to answer the question why. For this reason, some modern scientists write negatively in their popular books about the physics of, say, Aristotle and his contemporaries. But the natural instinct of Ancient Greek philosophers – shared by many people today – was to be driven by the search for causal reasons. Aristotle’s explanation of gravity depended, in other words, not on how things were attracted to the centre of the universe, but rather why this happened.
Aristotle believed that the four elements (earth, air, fire and water) each had their own natural tendencies. The reason why, for instance, an Earth-based object like a rock fell, he argued, was because its natural place was the centre of the universe (which meant the Earth). Aristotle tried to explain why the rock fell, not how it fell. Modern scientists can easily dismiss the philosopher’s explanation as irrelevant. But if they don’t understand the thought process behind the question, they miss a natural line of thinking for a non-scientist, which needs to be addressed rather than dismissed.
More fundamental for Hossenfelder than the language niggle, though, was the suggestion that scientists have “barely figured out how [gravity] works”. In her blog post, Hossenfelder responds that we do know how gravity works. “The purpose of science is to explain observations,” she writes. “We have a theory by the name General Relativity that explains literally all data of gravitational effects. Indeed, that General Relativity is so dramatically successful is a great frustration for all those people who would like to revolutionize science à la Einstein. So in which sense, please, do scientists barely know how it works?”
But answering the question “How?” itself merely generates a second-level question. If you said gravity works by warping space–time, the immediate response of a non-scientist would be: “Yes, but how does matter warp space–time?” And now physicists are stumped. They can’t answer that question, because repeatedly asking “How?” leads to a dead end.
Physicists may describe constructing a mathematical model as understanding, but it isn’t what most people mean by the word
To the public, science is about the search for simple truths that explain how nature functions and, as a result, possibly also getting some idea of the why. But when a physicist talks of understanding something, they have in mind being able to construct a model – usually mathematical – that matches, as closely as possible, the data that are observed. Physicists may describe this as “understanding”, but it isn’t what most people mean by the word. I feel it’s this lack of a shared vision between the public and the physics community that creates an inevitable barrier.
Offering lettuces to an ass
Let me explain Galileo (left) and Isaac Newton had very different ideas about communicating science to the public. (Courtesy: Left: Justus Sustermans 1636/National Maritime Museum, London; Right: Sheila Terry/Science Photo Library)
It can sometimes feel to the public that scientists are guilty of perpetuating the concept that wisdom should be kept from the masses. Writing in the 13th century, friar and proto-scientist Roger Bacon noted that Aristotle said “It is stupid to offer lettuces to an ass since he is content with thistles.” Bacon agrees, telling us that “The cause of obscurity in the writings of all wise men has been that the crowd derides and neglects the secrets of wisdom and knows nothing of the use of these exceedingly important matters.”
This philosophy comes through in Isaac Newton’s Principia, particularly when set alongside Galileo’s Two New Sciences. Each of these books is a masterpiece of physics. Yet the approach taken could not be more different. Galileo writes in his native language, Italian. His prose is accessible and his discussions of physical principles take the form of a three-way discussion between two experts (Salviati and Sagredo) and a third person, Simplicio. Presenting the voice of the ordinary man, Simplicio is the most interesting participant in this context. He asks the questions ordinary readers want answered, a simple device that enables Galileo to keep his text grounded.
By contrast, Newton writes in Latin, making his book less accessible to the non-expert. Indeed, Newton goes out of his way to make the book difficult to read. He notes that he originally intended the third part of the book, The System of the World, to be for a popular audience “so that it might be more widely read”. However, he then deliberately recast it to make it more obscure.
“Those who have not sufficiently grasped the principles set down here,” he remarks, “will certainly not perceive the force of the conclusions, nor will they lay aside the preconceptions to which they have become accustomed over many years; and therefore, to avoid lengthy disputations, I have translated the substance of the earlier version into propositions in a mathematical style, so that they may be read only by those who have first mastered the principles.”
Perhaps physicists should be a little more like Galileo and a little less like Newton when communicating with the public.
Delivering the goods
Getting a better feel for what the public’s questions mean isn’t the only prerequisite for good communication. Another danger is that if we take too much for granted, our explanations don’t deliver. In a recent book, A Farewell to Ice (2016 Allen Lane), Peter Wadhams – a sea-ice scientist and former professor of ocean physics at the University of Cambridge – tries to explain the concept of Fourier analysis to the reader. “The Fourier series,” he writes, “by which any function can be split into a set of harmonics…” – without thinking that anyone who knows what a function being split into harmonics involves probably knows about Fourier analysis. It’s a non-definition – a trap that many communicators fall into.
However, there is a further barrier when it comes to understanding and anticipating the questions the public might ask. When scientists are writing for the public they need to bear in mind the kind of questions that their words will generate in the mind of the reader and be prepared to answer those questions. Paradoxically, whereas using too many technical terms over-complicates an explanation, a lack of anticipation leads to over-simplification.
As an example, in his otherwise excellent book Neutrino Hunters (2013 Scientific American), Ray Jayawardhana – an astrophysicist at York University in Canada – describes the challenges facing people who build detectors for these elusive particles. Jayawardhana introduces us to a development of the Japanese Super-Kamiokande detector: “Beacom and his colleagues have suggested that dissolving a bit of gadolinium, a silvery-white metal, in the giant water tank at Super-Kamiokande would do the trick [of distinguishing supernova relic neutrinos], since the fix would enhance the detector’s sensitivity to relic neutrinos.” Then he moves on. Gadolinium is not mentioned again.
In that extract, we see Jayawardhana answering a potential reader question – “What is gadolinium?” – though, to be frank, giving the element’s colour feels a bit like asking what kind of car someone has and being told that it’s blue. However, the author leaves the reader mentally stranded. Jayawardhana knows the answers, but doesn’t share them. As a result, the reader is mired in questions that are never answered. How does gadolinium improve detection? How does this enable the detector to distinguish relic neutrinos from common-or-garden local ones? We don’t find out.
What is lacking here is an ability to pre-empt questions that the reader may have in response to a piece of writing, and then to formulate a response with which the lay person will be satisfied. Let me use one more example to show this barrier in action.
Mind the warp
A few years ago, I was researching my popular-science book Gravity (2012 St Martin’s Press). In the section on the general theory of relativity, I had to get across how it is that the warping of space–time produced by matter can lead to the effects that we experience as the force of gravity. Inevitably I wheeled out the “bowling ball on a sheet of rubber” analogy, which uses a flat sheet of rubber, stretched taut, as a 2D model of space.
Trampoline gravity A classic analogy used to explain gravity is a bowling ball on a sheet of rubber, where the ball represents an object such as a planet. But it’s important to point out that the rubber sheet represents space–time, not just space. (Courtesy: Shutterstock/Mopic)
We imagine a beam of light, or the straight-line motion of a planet flying free through space, as a coloured line on the surface of the sheet. We then place a bowling ball on the sheet and it distorts the rubber. As a result, the line is no longer straight. It curves around the ball. This, we say, is rather like the way that matter distorts space (though in 3D, rather than 2D), causing light and the straight-line motion of celestial bodies to bend around massive objects like stars and planets. At this point, traditionally, the popular account of gravity moves on. But there is a question that is not asked. To take Newton’s example: how does this make an apple fall?
If this is ever mentioned when using the rubber-sheet analogy, we usually get some hand-waving suggestion that the apple slides down the indentation in the rubber sheet towards the massive object. But what makes the apple move? Gravity – so we haven’t got anywhere. Because I couldn’t come up with a sensible extension to the rubber-sheet analogy, I e-mailed a wide range of physicists asking how they would explain, for the general public, how the apple goes from being stationary to falling.
Most academics didn’t respond. This might seem unsurprising, but, on the whole, professional scientists are happy to answer meaningful queries. The apparent implication here is that either the rubber-sheet analogy has been stretched too far or that the answer is just too complicated for little minds to worry themselves with. Where I did get replies, they tended to suggest my question was irrelevant or, well, the mathematics works, so let’s not worry about the analogy. A typical argument from those in the “irrelevant” camp” was: “A force is a force, of course, and asking why/how it causes an acceleration already seems a bit circular.” Asking how you can have a force producing action at a distance is not at all circular, but something that has worried people for a long time. There still needs to be a cause.
Finally, I got an explanation I could use from Friedrich Wilhelm Hehl of the University of Cologne in Germany. His initial explanation, admittedly, had limited value for the public: “As you correctly say, in the ‘bowling ball on a rubber sheet’ picture, the sheet represents space–time. In space–time the 4-velocity of a particle is just the tangent unit-4-vector of the path traced by the particle. Since a curve in the sheet at a certain point has always a tangent 4-vector, the particle has to follow the path with the corresponding 3-velocity.”
This was useful to know, I’m sure, but didn’t exactly illuminate things for the non-physicist. But after a little probing, Hehl translated this explanation into a more amenable form. By getting the reader to think not of distorting space but space–time, and thinking through the implications of warping the time dimension, which with nowhere else to go has to produce a change in the space dimensions, it was possible to extend the analogy to see how warped space–time could produce motion.
Lessons to learn
Altogether, I’d suggest that there are three significant lessons from these examples. First, if you get a question that doesn’t make sense to you, don’t simply assert that it is a silly question. More likely, it’s the scientist who is at fault for not understanding – not the questioner for being dumb. Ask for more detail. And if you still don’t get it, ask a friend who isn’t a physicist what it means. (If you don’t have any friends who aren’t physicists, get out more.) Ensure your answer takes into account the questioner’s viewpoint.
Try to break down what you are saying and identify where the assumptions are
Second, when you are explaining something, always try to be aware of your assumptions about what the questioner already knows. This can be difficult, because so much of what you assume has been part of your working life for so long. Try to break down what you are saying and identify where the assumptions are – then make sure that they are ones that hold for your audience too. If not, deal with them.
And finally, don’t over-simplify. We are used in academic writing to ensuring that statements are backed up by sources or experimental evidence. In public communication, it’s important to back up statements with explanations that the reader needs (and not just the explanations that you think you need). Provided you do explain appropriately, you can go into more detail than you might think. Many books on gravity for a lay audience don’t include Einstein’s field equations. Mine did – not because I felt the reader is ever going to do the maths, but to satisfy their curiosity of what these things look like and to explain the main elements of the equations, without straying into mathematical complexity.
If physicists are to communicate well with the public, we need to do more than just weed out jargon and simplify complex mathematics. We also need to understand the nature of the public’s questions, anticipating queries that are based on a different kind of thinking. It’s a stretch, but it is possible – and, I would argue, is essential if we want the public, which controls the purse strings, to support progress and advancement in physics.
Rerouting transatlantic flights to follow the most climate-friendly path could damage the climate 10% less for an increase in costs of just 1%. That’s according to a team from Germany, the Netherlands, Belgium, Norway and the UK.
“An attractive aspect of our approach is that it potentially enables some mitigation of aviation’s climate impact…using the current aircraft fleet,” Volker Grewe of the Deutsches Zentrum für Luft- und Raumfahrt, Germany, and Delft University of Technology in the Netherlands, explains. “Some mitigation options involve changes in aircraft or engine design, which would take decades to implement given the slow – and expensive – turnover of the global fleet.”
Volker and colleagues modelled routings for 800 daily flights across the Atlantic under five typical winter weather patterns and three typical summer patterns. The team combined the EMAC chemistry-climate model with an air-traffic simulator, choosing 85 variations for each flight path – 17 horizontal and five vertical. Then they picked the most “eco-efficient”, which is the path with the best ratio of climate-impact reduction to cost increase.
Multiple impacts
Aircraft have an impact on the climate by emitting carbon dioxide, water vapour, nitrogen oxide and particulates. These alter the concentration of the greenhouse gases ozone and methane, and also form contrails. Where and how high the plane is, as well as the time of day and season, all alter the size of its climate effect.
“It is now well established that – unlike the climate effects of CO2 – the non-CO2 climate effects such as contrail formation depend sensitively on when and where the aircraft emissions occur,” says Grewe, “and these sensitive regions vary in location and importance from day to day, as they are strongly influenced by the prevailing weather patterns.”
Contrails, for example, form if the hot, moist exhaust from the jet engine becomes saturated with respect to water when it mixes with the air in the atmosphere. And the trails only persist if the ambient air is saturated with respect to ice. Contrails affect both incoming radiation from the Sun and the exit to space of infrared radiation emitted by Earth and its atmosphere. On average, the trails cause warming, but close to sunrise and sunset they can result in cooling.
Ozone and methane
In general, aircraft emissions tend to boost the amount of ozone and decrease methane concentrations, with the warming from the extra ozone outweighing the cooling from the reduction in methane. But this varies a lot locally, and in some regions the emitted nitrogen oxides cause cooling.
“Put simply, if we can avoid those regions in the atmosphere where the non-CO2 emissions have the largest climate effect, we can reduce the climate impact significantly,” says Grewe. “Our modelling study showed that a large reduction of aviation’s climate impact is feasible at relatively low costs.”
Rerouting flights could cut their climate harm but may increase fuel and staff costs. Cost-efficient reductions in climate impact mostly resulted from avoiding the formation of warming contrails or from producing cooling contrails, Grewe and his colleagues found.
Close collaboration
Investigating such mitigation options requires close collaboration between atmospheric scientists and disciplines like air-traffic management, Grewe says. He believes all sectors must play a role in meeting the internationally agreed 2 °C target for the total climate effect of human activity.
“This is particularly challenging for the aviation sector, given the predictions of its continued growth over coming decades,” he says. “Hence, we need a combination of various mitigation options – technological, such as cleaner and more efficient engines, and operational, i.e. more eco-efficient routes. To make this happen, a political framework is required, which aims at limiting aviation impacts. It might be on an international or regional basis.”
Airlines would in all likelihood need regulations or a market incentive such as a price on climate impact to carry out such climate-friendly routing. While the International Civil Aviation Organisation (ICAO) has decided to implement the Carbon Offsetting and Reduction Scheme for International Aviation (CORSIA), non-carbon-dioxide effects are still not considered in political decisions to limit the climate effect of aviation, Grewe says.
Reliable forecasts
“Implementing our proposed approach…is likely to be at least 5–10 years in the future – it should be considered ‘exploratory’ at present,” he adds. “We have to convince all stakeholders that the approach is worthwhile and feasible in practice, and that the costs associated with it are proportionate. And because the location of the climate-sensitive regions varies markedly from day to day, we also need to clearly establish that we can reliably forecast these areas sufficiently far in advance, so that re-routing aircraft to avoid them can be done with confidence.”
Now the scientists, who included a road map in their paper in Environmental Research Letters (ERL), are looking for more funding. They are also participating in ATM4E, a European project investigating whether it’s possible to avoid climate-sensitive regions in areas with high traffic density, as well as how the approach can be made operational, included in a weather forecast system, and verified.
A new 2D material just one atom thick has been made by an international team of researchers led by Axel Enders. Dubbed hexangonal boron–carbon–nitrogen (h-BCN), the material could offer many of the benefits of graphene, which is a hexagonal lattice made of just carbon. But unlike graphene, h-BCN has a direct electronic band gap, which could make it useful for creating electronic devices.
First isolated in 2004 by Andre Geim and Konstantin Novoselov, who shared the 2010 Nobel Prize for Physics for their discovery, graphene is blessed with a wealth of potentially useful mechanical and electronic properties. Despite being so thin and flexible, graphene is much stronger than steel and is an excellent conductor of heat. Graphene also conducts electrons at extremely high speeds. As a result, it could be the ideal material for making electronic devices that are ultrafast, high-density and even bendable.
Mind the gap
Many of graphene’s electronic properties arise from the fact that it is a semiconductor with a zero-energy gap between its valence and conduction bands. This is not ideal for making transistors and other electronic devices because such circuits need semiconductors, such as silicon, that have a band gap. In an attempt to make a modified version of graphene that does have a band gap, device developers have therefore explored various schemes – including applying an electric field, adding chemical impurities or modifying the structure of graphene. None, however, has proved ideal.
Now, Enders and colleagues at the University of Bayreuth, University of Nebraska-Lincoln, University of Krakow, State University of New York at Buffalo, Boston College and Tufts University have developed a graphene-like material that could fit the bill. The team made h-BCN by heating an organic molecule containing boron, nitrogen and carbon on an iridium substrate. The result is an atomically thin layer of h-BCN that is corrugated because of the lattice mismatch between the layer and substrate.
Multiple techniques
The team studied the structure and electronic properties of the film using molecular-resolved scanning tunnelling microscopy imaging, X-ray photoelectron spectroscopy and low-energy electron diffraction. The researchers also used density functional theory and first-principles calculations to further understand h-BCN.
An important result of the measurements and calculations is the prediction that h-BCN should have a direct electronic band gap of a size that falls between that of gapless graphene and hexagonal boron nitride, which is an insulator. According to the researchers, this band gap could make the material better suited than graphene for electronics applications.
“Our findings could be the starting point for a new generation of electronic transistors, circuits and sensors that are much smaller and more bendable than the electronic elements used to date,” says Enders. “They are likely to enable a considerable decrease in power consumption.”
An atom could be made to emit an optical signal that is usually associated with another type of atom, according to calculations done by Andre Campos, Denys Bondar, Herschel Rabitz and Renan Cabrera at Princeton University in the US. When an atom is illuminated with light it can absorb energy and give off light at a set of frequencies distinct to that type of atom – which forms the basis of optical spectroscopy. However, if the atom is illuminated by an intense and complex optical signal it should be possible – in principle – to control the quantum states of the atom and cause the emission of light at frequencies not normally seen from that atom. Unlike conventional spectroscopy, a measurement of such a spectrum would not reveal the type of the atom – unless the experimenter knew the precise nature of the complex optical signal. Previous attempts to calculate the exact nature of such an optical signal has proven very difficult. But now, the team has come up with a successful scheme that involves both bound and ionized quantum states of an atom. Writing in Physical Review Letters, the team points out that some of the experimental techniques needed to carry out its scheme have already been demonstrated in the lab.
Five-loop QCD calculated at long last
A quantum chromodynamics (QCD) calculation involving five loops has been made for the first time by physicists in Russia and Germany. QCD describes the strong nuclear force between the quarks that make up protons, neutrons and other heavy particles. It is notoriously difficult to calculate the properties of systems governed by QCD because of the enormous strength of the strong nuclear force and the fact that calculations must consider large numbers of virtual quark–antiquark pairs that pop into and out of existence. As a result, physicists have struggled to calculate the properties of even simple objects such as the proton. Since the early 1970s, physicists have shown that QCD calculations can be made as a series of corrections to a leading-order calculation. These corrections are called loops, and physicists had been able to calculate one-, two-, three- and four-loop corrections. However, progress had been stuck at four loops since 1997. Now, Pavel Baikov at the Skobeltsyn Institute of Nuclear Physics in Moscow and Konstantin Chetyrkin and Johann Kühn of the Karlesruhe Institute of Technology have extended calculations to five loops. Writing in Physical Review Letters, the trio use five loops to calculate several properties of the Higgs boson.
Metamaterial bricks shape sound
These metamaterial bricks can be placed together to create a new supermaterial that can manipulate sound. (Courtesy: Interact Lab / University of Sussex)
A new “supermaterial” has been made that can bend and shape sound waves using specially designed bricks. Scientists at the University of Sussex and the University of Bristol in the UK have developed an acoustic device that can transform incoming sound waves into any required sound field. Sound manipulation is useful for many applications including ultrasound imaging, loudspeaker design and acoustic levitation. Current approaches use fixed lenses and expensive phased arrays. In contrast, this latest device comprises small, 3D-printed metamaterial bricks. These slow down incoming sound by directing it through meandering channels. The tailored geometries of the channels delay the wave phase to create the desired sound field. Gianluca Memoli from the Sussex team describes the device as a “do-it-yourself acoustics kit”, as the bricks are easily made and can be arranged in arrays specific to the application requirements. The new material could be used on a large scale to direct and focus sound to form an audio hotspot. It could also be suitable for small-scale applications such as focusing high-intensity ultrasound waves to destroy tumours within the body. The material is presented 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 a new graphene-like material.
Tiny bubbles: a laser-made mermaid. (Courtesy: Kota Kumagai/ Utsunomiya University)
By Hamish Johnston
A popular way of melding science and art is to create an image of a mythical being in your lab. Yoshio Hayasaki and colleagues at Utsunomiya University in Japan have made a pretty good likeness of a mermaid using a laser that forms tiny bubbles inside a liquid. “In our display, the microbubble voxels are three-dimensionally generated in a liquid using focused femtosecond laser pulses,” explains team member Kota Kumagai.
A new way of beating the diffraction limit in optical microscopy has been unveiled by physicists in Australia and China. The technique makes use of nanoparticles to improve the efficiency of stimulated emission depletion (STED) microscopy, allowing it to be used with lower levels of illumination than previously possible.
STED microscopy was developed by the Germany-based physicist Stefan Hell, who won one third of the 2014 Nobel Prize for Chemistry for his work on the technique. The technique allows features much smaller than the wavelength of light to be observed with a microscope – something that is impossible with conventional microscopes.
Doughnut’s hole
STED involves tagging regions of interest in a sample with fluorescent molecules and using a beam of light to cause the molecules to emit light. A second “depletion” beam of light is focused to a doughnut shape in the sample and suppresses the fluorescence everywhere in the focal region – except at the doughnut’s central hole. By scanning the beams jointly over the sample, the spatial distribution of the fluorescent molecules can be determined at resolutions much smaller than the wavelength of the light used.
The resolution of STED improves as the intensity of the depletion beam increases. However, if the depletion beam is too powerful it will heat up the sample and destroy it – and this puts a practical limit on the resolution that can be achieved.
Now, Peng Xi, Dayong Jin and colleagues at Macquarie University and several other institutes in Australia and China have got around this problem by using lanthanide-doped upconversion nanoparticles (UCNPs) in place of fluorescent molecules. UCNPs are tiny crystals – as small as 13 nm across in this particular study – that absorb two or more long-wavelength optical photons and then emit one shorter wavelength photon.
Blue light
When illuminated with near-infrared light at 980 nm, the team’s UCNPs emit blue light at 455 nm. However, when a near-infrared depletion beam at 808 nm is also fired at the nanocrystals, a stimulated emission process causes the UCNPs to stop emitting blue light and emit near-infrared light instead.
To see if the UCNPs are appropriate for STED, the nanocrystals were dispersed in a medium that was specifically formulated for fluorescence microscopy. The team then used STED to image the UCNPs at a spatial resolution of about 28 nm, which is much shorter than the wavelengths of the light used by the microscope. To achieve similar resolution using traditional STED techniques would require a much more intense depletion beam, say the researchers. Another benefit of using the UCNPs is that the near-infrared light can be supplied by two simple diode lasers.
However, the technique does have some downsides. The intensity of blue light given off by the UCNPs is much lower than the light produced in conventional STED, which means that it takes about 10 times longer to acquire an image. Further work must also be done to ensure that the nanoparticles will only tag specific regions of a sample. The researchers must also ensure that the UCNPs do not stick together when dispersed in a sample.
Exploding frozen water droplets have been filmed at high speed. As a droplet of water freezes from the outside in, it can explode in a shower of ice shards. Although the phenomenon is known to be caused by the self-confinement of the initial ice shell and expansion of the water inside as it solidifies, the mechanisms leading to the explosion are mostly unknown. A team from the University of Twente in the Netherlands has used high-speed cameras and computer modelling to study the event from the formation of the first ice crystals to the moment the droplet bursts. To do so, they supercooled millimetre-size droplets in a specially designed chamber. This meant that the water was below freezing point but free from ice crystals – which ensured a reproducible starting point for the experiments. Sander Wildeman and colleagues then triggered the freezing process by touching the droplet with a small tip. This caused a shell of ice to encapsulate the drop within microseconds. As the liquid water within the centre becomes compressed by the shell expanding inwards, the shell itself undergoes intermediate fracturing and healing. Furthermore, the scientists observed that some of the pressure is released as an “arm” of ice that extends from the droplet. Within about 2 s, the droplet shatters and sprays ice shards at a velocity in the order of 1 m/s. Using computer modelling, the team concluded that the droplets only explode if their diameter is larger than 50 μm. Below this, the surface tension of the ice shell is strong enough to balance the internal pressure and keep the droplet intact. The study, described in Physical Review Letters, could help in understanding how hail and other precipitation form.
Innovative and inspiring: biophysicist Patricia Bassereau. (Courtesy: Institute Curie Research Centre)
The Autumn-Winter 2016 Emmy Noether Distinction for Women in Physics prize has been given to Patricia Bassereau of the Institute Curie Research Centre in Paris, France. Awarded by the European Physical Society, the prize was given to Bassereau for “her important and innovative work on the studies of soft matter and in vitro biological systems at the forefront of biophysics. Her rich and fruitful career is an inspiration for young women researchers.” Bassereau leads the Membrane and Cell Functions research group at the Institute Curie, where she is currently working on the physics of biological membranes including non-equilibrium systems, molecular motors and biomimetic systems. Describing the importance of mentorship for women embarking on careers in science she says: “I have been lucky to meet great scientists who gave me advice, helped me gain self-confidence and also believed I could perform interesting science.”
Bright gamma-ray sources spotted at centre of Andromeda
The centre of the Andromeda galaxy as seen by the Fermi Gamma-ray Space Telescope. The yellow and white regions have the most intense gamma-ray emissions. (Courtesy: Credit: NASA/DOE/Fermi LAT Collaboration and Bill Schoening, Vanessa Harvey/REU program/NOAO/AURA/NSF)
Most gamma rays emanating from the Andromeda galaxy come from its centre, rather than throughout the galaxy, as previously expected. That is the conclusion of astronomers who have used NASA’s Fermi Gamma-ray Space Telescope to study Andromeda, which at 2.5 million light-years distance is the nearest major galaxy to Earth. The result is reminiscent of the previous – and unexpected – observation by Fermi that there is an excess of gamma rays coming from the centre of the Milky Way. The astronomers have proposed several explanations for the Andromeda observation. One is that the gamma rays are produced by the decay of hypothetical dark-matter particles, which are expected to concentrate at galactic centres. Another is that there may be an unexpectedly high concentration of pulsars at the centre. These are spinning neutron stars that emit copious gamma rays. The next step for the team is to look at X-ray and radio emissions, which could help scientists work out if the gamma rays are indeed produced by pulsars. The observations are described in The Astrophysical Journal.
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Uranium has been extracted from seawater using electrochemical methods. A team at Stanford University in California has removed the radioactive material from seawater by using a polymer–carbon electrode and applying a pulsed electric field.
Uranium is a key component of nuclear fuel. On land, there are about 7.6 million tonnes of identified uranium deposits around the world. This ore is mined, processed and used for nuclear energy. In contrast, there is 4.5 billion tonnes of the heavy metal in seawater as a result of the natural weathering of undersea deposits. If uranium could be extracted from seawater, it could be used to fuel nuclear power stations for hundreds of years. As well as taking advantage of an untapped energy resource, seawater extraction would also avoid the negative environmental impacts of mining processes.
Tiny concentrations
Scientists are therefore working on methods to remove and recover uranium from the sea. However, the oceans are vast, and the concentration of uranium is only 3 μg/l, making the development of practical extraction techniques a significant challenge. “Concentrations are tiny, on the order of a single grain of salt dissolved in a litre of water,” says team member Yi Cui. Furthermore, the high salt content of seawater limits traditional extraction methods.
In water, uranium typically exists as a positively charged uranium oxide, or uranyl, ion (UO2+2). Most methods for extraction involve an adsorbent material where the uranyl ion attaches to the surface but does not chemically react with it. The current leading materials are amidoxime polymers. The performance of adsorbents is, however, limited by their surface area. As there are only a certain number of adsorption sites, and the concentration of uranium is extremely low compared with other positive ions like sodium and calcium, the uranium-adsorbent interaction is slow and sites are quickly taken up by other ions. Furthermore, the adsorbed ions still carry a positive charge and therefore repel other uranyl ions away from the material.
Electrochemical answer
Cui and his team turned to electrochemistry and deposition for a solution to this problem. In a basic electrochemical cell, there is an electrolyte solution and two submerged electrodes connected to a power supply. By providing the electrodes with opposite charges, an electrical current is driven through the liquid, forcing positive ions to the negative electrode, and electrons and negative ions to the positive electrode. At the negative electrode, called the anode, the positive ions are reduced, meaning they gain electrons. For most metallic ions, this causes the precipitation of the solid metal and is often deposited on the electrode surface.
In their electrochemical cell, the team used an anode made of carbon coated with amidoxime polymer, and an inert partner electrode. The electrolyte was seawater, which for some tests contained added uranium. By applying a short pulse of current, the positive uranyl, calcium and sodium ions were drawn to the carbon–polymer electrode. The amidoxime film encouraged the uranyl ions to be preferentially adsorbed over the other ions. The adsorbed uranyl ions were reduced to solid, charge-neutral uranium oxide (UO2) and once the current was switched off, the unwanted ions returned to the bulk of the electrolyte. By repeating the pulsed process, the researchers were able to build up the deposited uranium oxide on the electrode surface, no matter what the initial concentration of the solution was.
Removal and recovery
In tests comparing the new method to plain adsorptive amidoxime, the electrochemical cell significantly outperformed the more traditional material. Within the time it took the amidoxime surface to become saturated, the carbon–polymer electrode had extracted nine times the amount of uranium. Furthermore, the team demonstrated that 96.6% of the metal could be recovered from the surface by applying a reverse current and an acidic electrolyte. For an adsorption material, only 76.0% can be recovered with acid elution.
Despite the researchers’ success, there is a long way to go before large-scale application. To be commercially viable, the benefits of the extracted uranium must outweigh the cost and power demands of the process. Furthermore, the process needs to be streamlined to treat large quantities of water. “We have a lot of work to do still but these are big steps toward practicality,” Cui concludes.
The extraction method is described in Nature Energy.
Cubic breakdown: rhodium nanocubes break down carbon dioxide when illuminated. (Courtesy: Chad Scales)
Carbon dioxide has been converted to methane by illuminating rhodium nanoparticles with ultraviolet light. Using light to break down carbon dioxide (CO2) in the atmosphere is a long-sought-after mechanism. Not only could it start reducing the environmental impact of human CO2 emissions, the methane could be used as a renewable source of energy. Scientists at Duke University in the US have broken apart CO2 using tiny, cubic rhodium particles and ultraviolet light. Rhodium is a rare, inert metal that is already used in small amounts to speed up chemical processes in industry. To catalyse such reactions, an extra energy input is required and heat is typically used. Using rhodium nanoparticles, Jie Liu and team compared the breakdown of CO2 using heat and ultraviolet light. They found that not only is the reaction more efficient when using light, it almost exclusively produced methane rather than a mix with carbon monoxide. The group suggests that the light generates energetic electrons that activate the necessary intermediates for methane production, while barely affecting chemical bonds involved in carbon-monoxide production. Next, the team hopes that tweaking the size of the nanoparticles will mean that sunlight can power the reaction. The work is presented in Nature Communications.
UK invests £229m in new research institutes
The Sir Henry Royce Institute for Advanced Materials will open in 2019. (Courtesy: University of Manchester)
The UK government has announced it will provide £129m for a new materials centre located at the University of Manchester. Once open in 2019, the £150m Sir Henry Royce Institute for Advanced Materials will perform research in a range of areas from 2D materials to advanced metals processing, nuclear materials and energy storage. The institute was first mooted in 2014 by former UK Chancellor George Osborne and in late 2015 it was revealed that Julia King, a former chief executive of the Institute of Physics, which publishes Physics World, will chair the new centre. Meanwhile, the UK government has also announced that it will invest £103m in the Rosalind Franklin Institute – a new hub for life and physical sciences. Based at Harwell in Oxfordshire, it will be led by optical physicist Ian Walmsley from the University of Oxford. The institute, together with seven other partner sites, will aim to develop new technologies to tackle major challenges in health and life sciences, such as developing new treatments for chronic diseases.
Rotation sensor could be made from interfering ions
A proposal for a compact yet highly sensitive device that detects rotation using ions has been unveiled by physicists in the US. The sensor, which has yet to be built in the lab, is based on a Sagnac interferometer. This involves splitting a wave into two signals and sending the signals in opposite directions around a ring before recombining the signals at a detector. A change in how the interferometer is rotating will affect how the two signals interfere at the detector. This Sagnac effect is already used in optical gyroscopes in which light is sent in opposite directions around a coil of optical fibre. Now, Wes Campbell and Paul Hamilton of the University of California, Los Angeles, have proposed a scheme that uses ions to make an accelerometer that should combine high sensitivity with very small size. The wave–particle duality of quantum mechanics means that the ions behave like waves as they travel through the interferometer – which is based on an ion trap. Crucial to the success of the design, according to Campbell, is that the matter waves complete many circuits of the interferometer – much like light in a fibre coil. This would allow a practical device to be made much smaller than existing matter-wave gyroscopes, which are based on beams of atoms. If built, their device is expected to be as sensitive as existing commercial optical gyroscopes. However, writing in Journal of Physics B: Atomic, Molecular and Optical Physics, Campbell and Hamilton say that the performance could be improved. Although the device is only sensitive to changes in rotation, Campbell says it could be possible to use an ion trap to create a linear accelerometer. This could be paired with a rotation sensor to create GPS-free navigation systems that could be used on spacecraft and other vehicles used in locations where GPS is not available.
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 extracting uranium from seawater.
