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Nuclear diamonds: the ultimate long-life battery?

The proposal comes from a group of researchers at the University of Bristol in the UK, who say they have a practical way of dealing with some of the nearly 95,000 tonnes of radioactive graphite that was used as a moderator in the UK’s nuclear reactors. Applications of such devices could include long-lasting power supplies for pacemakers and even a lightweight power supply for space missions.

Unsurprisingly, this eye-catching research captured the attention of specialist and mainstream media publications alike when it was announced towards the end of 2016. In this podcast, we probe deeper into the science behind the headlines.

The episode is presented and produced by Andrew Glester, a science communicator based in Bristol, who says he takes a “sceptical optimism” to such bold scientific claims. Glester visits the research team at the University of Bristol to find out more about the proposal – its applications, nuclear safety concerns, and the challenges that stand in the way of this idea becoming a practical reality.

Flash Physics: Circuits survive on Venus, electronics powered by stomach acid, Israel tops global R&D spend

Photographs of an integrated circuit before and after testing — Hot stuff: circuits before and after testing. (Courtesy: NASA)

Integrated circuits smash survival record in Venusian atmosphere

Integrated circuits that could withstand the harsh conditions on Venus for a record-breaking length of time have been built and tested by researchers at the NASA Glenn Research Center in Cleveland, Ohio. Operating a lander on the surface of Venus is a very difficult task because the temperatures there can reach 460˚ C and the pressure of the caustic atmosphere is about 100 times that of Earth’s. This vicious environment quickly destroys electronic circuits – even if they are cocooned in heat- and pressure-resistant vessels – and the best systems have only survived for a few hours on Venus. Creating circuits that can resist the Venusian atmosphere for longer and without the need for heavy and cumbersome shields is the goal of NASA’s Phil Neudeck and colleagues. They have created a new integrated circuit from silicon carbide (SiC), which is an extremely tough, chemically inert and heat-resistant semiconductor. They made two ring-oscillator integrated circuits from SiC junction field-effect transistors and tested them in the Glenn Extreme Environments Rig, which can simulate conditions on Venus. The chips survived for more than 500 h while exposed directly to the harsh environment, with no cooling and no protective chip packaging. “Both integrated circuits still worked after the end of the test,” Neudeck says. The work is described in AIP Advances.

Electronic capsule powers itself with stomach acid

Photograph of the ingestible electronic device — Ingestible electronic device powers itself for several days using biocompatible galvanic cells. (Courtesy: Diemut Strebe)

A new ingestible electronic device can harvest energy inside the gastrointestinal (GI) tract, allowing it to monitor temperature over several days. In recent years, the technology behind ingestible electronics has significantly improved. These small devices can take live images of the GI tract, deliver drugs and measure conditions such as pH and temperature. However, powering the devices for more than a few hours remains challenging. Now, a team led by Giovanni Traverso of the Massachusetts Institute of Technology (MIT) and Harvard Medical School has developed a capsule that uses biocompatible galvanic cells. The cells harvest energy from the GI tract by transferring electrons between metallic electrodes and the gastric or intestinal fluid. The process can power the device for several days, allowing it to monitor temperature and send data wirelessly to the researchers. The electronic capsule could be used for diagnosis and treatment, and the team hopes to combine the technology with other sensors. A more detailed report on the work presented in Nature Biomedical Engineering can be found on nanotechweb.org.

Israel tops global R&D spend

Israel put 4.3% of its gross domestic product (GDP) into R&D in 2015, making it the biggest spender – in terms of the percentage of its economic output – of the 35 countries belonging to the Organisation for Economic Co-operation and Development (OECD). Israel just surpassed South Korea, who ploughed 4.2% of the country’s GDP into science, while Japan was third (3.5%). The US, meanwhile, spent 2.8% of its GDP on R&D, with China spending 2.1%. In Europe, Sweden was the highest at 3.3% followed by Austria at 3.1%. The UK, meanwhile, spent 1.7% of its GDP on R&D, below the EU average of 2.1% and the OECD average of 2.4%. The OECD says that there was a slight decline in government R&D budgets in 2015 but businesses increased their contribution by 2.5%, making the private sector responsible for nearly 70% of all R&D spending that year.

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 atomic friction.

Joel’s conference

Just as it had on the previous 115 occasions, the event opened with a bell carried by Joel Lebowitz. The 86-year-old physicist, often fondly called “the soul of statistical mechanics”, strode through the lobby of the Hill Center at Rutgers University’s Busch campus in New Jersey, clanging the bell to summon the animated coffee drinkers to the lecture hall. The 116th Statistical Mechanics Conference, held on 16–18 December last year, was about to begin.

Lebowitz’s biannual conferences are remarkable not only for their longevity – they have run since 1959 – but also for their egalitarianism and diversity. What’s more, the meetings, along with the Journal of Statistical Physics that Lebowitz has edited for the past 40 years, have helped the field of statistical mechanics to survive the forces threatening to fragment it into subfields.

Lebowitz: a life

Born in 1930 in a small town in what was then Czechoslovakia, Lebowitz’s native tongue was Yiddish. Life was tough in a Jewish community in this part of the world, but grew grimmer after the German occupation during the Second World War. Lebowitz’s family was sent to Auschwitz; only Joel – then aged 15 – survived. Thanks to a project to help orphaned children headed by Eleanor Roosevelt, Lebowitz obtained a visa to the US. He graduated from Brooklyn College in 1952, and was introduced to statistical mechanics, getting his PhD in physics from Syracuse University in 1956.

Outgoing and unflappable, Lebowitz readily collected friends. One was an artist and teacher named Kate Millett, who later became a famous feminist author. In her 1974 memoir Flying, Millett refers to Lebowitz under the pseudonym Jacob, describing him as “a charming Slavic soul with an insatiable taste for women and a tattoo on his arm from Auschwitz”.

In 1959, while at Stevens University of Technology in New Jersey, Lebowitz hosted his first informal conference on statistical mechanics. It was well received; the only alternatives, he told me at the most recent event, were formal conferences. Lebowitz continued the meetings, twice-yearly in May and December, after moving to Yeshiva University in Manhattan in the autumn of 1959. Talks were limited to five minutes and anyone who wanted could give one.

“Joel’s conferences were no-frills, geared for locals and on a single day,” recalls Pierre Hohenberg, a physicist then at Bell Labs. “You took the subway, no accommodation, no invited speakers, no Vugraphs [plastic sheets on which one could print or write and display with the aid of an overhead projector] and no food. They brought together a broad cross-section of the community and were how you kept up on the field.” Between 50 and 100 people would attend in the early years.

In 1977 Lebowitz moved to Rutgers. Many regular attendees were horrified: Rutgers was in the New Jersey countryside, you needed a car to get there and you had to stay overnight in a dilapidated hotel. Afraid the conferences would lose either their informal character or their audience, Hohenberg and others lobbied to continue the conferences at Yeshiva. Instead, Lebowitz rethought it.

He added invited speakers and celebrations of senior leaders in the field. If people stayed over, it might as well be a two-day (eventually three-day) conference. Amenities included meals and musical events. Finally, he flirted with formality by allowing Rutgers attendees to use Vugraphs. “That was a big ideological transition,” Hohenberg told me.

But Lebowitz continued to ensure that the conferences reflected the field’s diversity. At the start of his career, statistical mechanics was mainly concerned with effects on equilibrium processes in microscopic systems and scientists had only a data-driven grasp of phase transitions. The 1970s development of the renormalization group supplied a physical/mathematical understanding of phase transitions and scaling, which strengthened the difference between the mathematical side of statistical mechanics – involving exactly solvable models – and its physical side, allied with experimentation. The renormalization group also provided calculational techniques for scaling non-equilibrium systems that helped give statistical mechanics a broader range of applications. Lebowitz’s inclusive conferences embraced a spectrum of them.

At the December 2016 meeting, for instance, invited talks were given on statistical mechanics-related aspects of earthquakes, superconductors, liquid crystals, swimming particles, number theory, HIV, quantum mechanics and nacre – the beautiful iridescent material on the inside of certain molluscs. The spirit of the original Yeshiva format was retained in a morning session of five-minute talks on the behaviour of everything from electrons to microbes. As always, anyone who wanted to could give one of these talks, as long as you didn’t use Vugraphs or PowerPoint and erased the blackboard afterwards.

Lebowitz introduced each speaker, asked pointed questions and when speakers exceeded the allotted time, stood up and smiled until his genially expressed moral authority brought them to a halt. “It’s a one-man show, yet democratic and egalitarian,” Nihat Berker, an emeritus professor at the Massachusetts Institute of Technology, told me. “You don’t often see that.”

One talk is always devoted to human rights; this time Lebowitz gave it himself. “These are not good days for human rights,” he warned, mentioning recent cases involving individuals in Iran, the US, Egypt, China, Pakistan, Saudi Arabia and Turkey.

The critical point

Lebowitz’s meetings are ideal for our modern world, where researchers want to communicate their results and learn new ones – fast. Indeed, the standard scientific-conference format of concurrent sessions of PowerPoint-driven papers seems to me obsolete. Joel’s conference offers one successful alternative; the Gordon conferences, which have many imitators, are another. These reveal not only the continuing value of conferences in an electronic age but also the importance of leadership for creating a truly effective meeting.

Entanglement boosts data transmission

The efficiency of data transmission through ordinary optical fibres has been enhanced using a quantum-mechanical technique known as superdense coding. Physicists in the US have shown that they could nearly double the capacity of a fibre link compared with conventional transmission – and the researchers say their work could increase how much data the internet can handle.

Superdense coding exploits the phenomenon of entanglement to double, at least in principle, the capacity of an information channel. A single binary bit sent down a channel can normally encode two possible values – 0 or 1. But a single quantum bit, or qubit, that is entangled with a second qubit some distance away can instead encode four possible values. This is because the two particles, even though spatially separated, are strongly correlated with one another and so effectively act as a single entity. The total information transmitted is therefore equivalent to that of two classical bits.

First demonstrated experimentally in 1996, superdense coding involves two people – usually known as Alice and Bob – sharing a pair of photons that have their polarizations entangled. Alice then operates on her photon, her part of the quantum state, to prepare one of four quantum states jointly held with Bob. When Bob receives Alice’s photon, he holds the complete state, he can determine which of the four states is present using a complete Bell state measurement.

Notoriously difficult

However, these “Bell-state measurements” are notoriously difficult to do. Usually Bob can at best only make out two of the four possible states that he is trying to distinguish. With the remaining two considered unidentifiable he effectively has three of the four possible values to play with. This means the channel has a maximum capacity of about 1.59 bits, rather than the two bits that are theoretically possible.

One way to get around this is to use “hyperentanglement”, which involves entangling the particle pair together using two degrees of freedom, rather than just one. This allows Bob to differentiate between all four possible outputs. This was demonstrated in 2008 by researchers at the University of Illinois at Urbana-Champaign in the US, who used pairs of photons entangled simultaneously in spin and orbital angular momentum. They achieved what was then a record of 1.63 bits per channel.

The Illinois team carried out its experiments by firing laser beams through free space. Pointing out that atmospheric turbulence quickly destroys photons’ orbital angular momentum states, they concluded that their set-up was probably only suited for data transmission between satellites.

Special interferometer

The latest work, in contrast, shows the potential of superdense coding for use across fibre-based communication networks. Travis Humble, Brian Williams and Ronald Sadlier of the Oak Ridge National Laboratory in Tennessee used a specially designed interferometer to entangle the arrival times, as well as the polarization, of pairs of photons. In this way they showed they could increase the channel capacity of a 2 m long piece of standard optical fibre cable, using standard photon detectors to carry out the measurements. They report a new record of 1.67 bits per channel, demonstrating the feasibility of their approach by sending a 3.4 kilobyte image of an oak leaf – their lab’s logo – with a fidelity of 87% (see figure).

“What is nice about our demonstration is that we were able to use off-the-shelf equipment,” says Williams. As to the relatively small gain over the previous record, he explains that the higher the capacity, the harder it becomes to improve that capacity. “People can run a four-minute mile but no-one will ever run a three-minute mile,” he says by analogy.

A remarkable breakthrough for a useful realization of superdense coding over fibre
Julio Barreiro, University of California, San Diego

Julio Barreiro of the University of California, San Diego, who was part of the 2008 Illinois team, characterizes the earlier research as a “proof-of-principle demonstration”. In contrast, he says, the latest results constitute “a remarkable breakthrough for a useful realization of superdense coding over fibre”.

Humble says that the research could in principle increase the bandwidth of large swathes of the internet. But he notes that there are significant technical challenges to overcome, including the fact that superdense coding requires much lower power levels than are used in today’s fibre networks in order to limit channel noise. Low power levels increase the cost of deployment significantly, making it unlikely that the quantum technique would be used for mainstream data transfer.

Standalone quantum networks

Instead, Humble believes that standalone quantum networks could prove cost effective when it comes to specialist applications such as synchronizing atomic clocks around the world or setting up networks for high-performance computing. He adds that a partner organization of his group, the United States Army Research Laboratory, plans to build a standalone quantum network within the next three years.

The research is described in Physical Review Letters.

Flash Physics: Starlight closes Bell loophole, elusive white dwarf pulsar, St Andrews champions gender equality

Starlight closes Bell loophole

A Bell test of quantum entanglement that claims to use starlight to close the “freedom of choice” loophole has been done by an international team of physicists. Entanglement is a curious consequence of quantum mechanics that allows two particles to be connected in a way that cannot be described by classical physics. Entanglement is observed as correlations between measurements made on two particles (such as their polarizations) and in 1964 John Bell described his famous test of whether such correlations are stronger than those allowed by classical physics. Since then, physicists have done many Bell test experiments that confirm entanglement. However, no experiment is perfect and researchers have come up with a number of experimental “loopholes” that could allow purely classical phenomena such as faulty detectors to affect the outcome. In 2015, physicists were able to simultaneously close two important loopholes called “fair sampling” and “locality”. Freedom of choice is another important loophole that involves how the measurements are done. In a Bell test on entangled photons, a large number of measurements are made on different entangled pairs in which the direction of the polarization measurement is selected at random. If, for some reason, the polarization selection is not random but correlated to other aspects of the experiment, then the outcome of the Bell test could be affected. Now, Johannes Handsteiner and Anton Zeilinger of the University of Vienna and colleagues worldwide have used the random nature of starlight to close this loophole. Two telescopes at two locations separated by nearly 2 km were pointed at two different stars. The colour of the starlight changes in a random manner and this was used to decide how to set Bell test polarization detectors. The stars were chosen so that their light arrives at their respective telescopes first, before reaching other parts of the experiment. This, and the fact that the starlight light was created hundreds of years ago and very far away from Earth, allowed the physicists to conclude that there is no correlation between the choices of polarization measurement and the rest of the Bell test experiment. However, writing in Physical Review Letters, they point out that their experiment does not close the fair sampling loophole.

Elusive white dwarf pulsar strikes out at red dwarf neighbour

Artist impression of the AR Scorpii binary system, containing a white dwarf pulsar and red dwarf — A white dwarf pulsar has been observed for the first time in the AR Scorpii binary system. (Courtesy: Mark Garlick/University of Warwick)

The first white dwarf pulsar has been discovered after half a century of searching. Astronomers at the South African Astronomical Observatory in Cape Town and the University of Warwick in the UK have identified an elusive white dwarf version of a pulsar within the AR Scorpii binary system. Traditionally, a pulsar is a neutron star that emits beams of radiation due to its strong magnetic field and rapid spin. From Earth, the highly directional beams are seen as pulses of radiation. While a neutron star is the collapsed core of a massive star, a white dwarf results from smaller stars and astronomers have been searching for a white dwarf pulsar for more than 50 years. The AR Scorpii binary system studied by David Buckley and colleagues contains a white dwarf that is a similar size to Earth but 200,000 times more massive, alongside a cool, low-mass red dwarf star. The two are around 1.4 million km apart (three times the distance between the Moon and Earth) and orbit each other in 3.55 h. The white dwarf spins every 1.97 min and emits powerful beams of electrical particles and polarized radiation that are created in a similar manner to neutron star pulsars. The researchers have also established that the high-energy beams strike the companion star, exciting and accelerating electrons in the atmosphere to nearly the speed of light. This causes further pulses of radiation, from ultraviolet to radio wavelengths, in time with the white dwarf rotation. This means the entire system seems to pulse when observed from Earth. The current work is presented in Nature Astronomy and the team hopes further studies will help determine the exact mechanisms of the red dwarf’s atmospheric interactions as well as further disentangle the signals from the white dwarf pulsar and its companion.

St Andrews named a champion of gender equality

The Institute of Physics (IOP) has named the School of Physics and Astronomy at the University of St Andrews as a Juno Champion. Project Juno is an IOP initiative to address the underrepresentation of women in university physics and encourage gender equality. The project rewards departments across the UK and Ireland for promoting an inclusive atmosphere, ensuring that both women and men have equal opportunities at all levels of academia and providing supportive and flexible working practices. St Andrews has become the 17th university to achieve Champion status, the highest of the three Juno awards after Supporter and Practitioner. “The school has worked hard to deliver on our goals for equality of opportunity and reward for all staff and students,” explains Graham Turnbull, head of the School of Physics and Astronomy at St Andrews. Other Juno Champions include physics departments at the University of Cambridge, the University of Birmingham and Imperial College London.

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 quantum information.

Juan Morante: an energetic man

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By Matin Durrani

Juan Morante, who’s boss of the Catalonian Institute for Energy Research (IREC), visited the headquarters of IOP Publishing, which publishes Physics World, late last year. Morante has also just taken up the reins as the new editor-in-chief of the Journal of Physics D and was here to discuss everything about the journal, from commissioning and peer review to design and marketing.

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Your future with physics

By Margaret Harris

In a typical month, the careers section of Physics World features the stories of two different physicists: one who is working in a physics-related field (such as engineering or teaching), and another who decided to do something totally different (such as designing sailboats or running a winery).

I find these stories endlessly fascinating, and when I was Physics World’s careers editor, I loved sharing them with the wider physics community. But the section isn’t there just to add human interest. It’s also giving current students (and later-career physicists seeking a change) a better idea of what they could do with their physics knowledge in the workplace.

After talking to students and careers professionals, I realized that publishing two stories in the magazine once a month wasn’t really the ideal way of doing this – at least, not for readers who are actively looking for careers ideas, and who might therefore prefer to learn about lots of different options at once.

So with these readers in mind, we’ve come up with a brand-new publication for 2017. The first edition of Physics World Careers contains a selection of the best articles published in the magazine’s careers section last year, plus an extensive employer directory.

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‘Atomtronic’ battery made from Bose–Einstein condensate

A battery-like device that supplies a current of ultracold atoms has been created by physicists at the University of Colorado in Boulder. Their “atomtronic” battery is based on a Bose–Einstein condensate (BEC) and could be used to supply circuits made from transistors and other components that operate using atomic rather than electronic currents. Potential applications of the battery include inertial sensing and quantum-information processing.

Atomtronics is a new field of applied physics that aims to create analogue and logical circuits using currents of atoms. According to Boulder’s Dana Anderson, “practical devices do not yet exist”, and his team is focused on developing an atom transistor and simple transistor circuits. In 2016 Anderson and colleagues reported the development of an atomtronic transistor based on a magneto-optical trap that contains three potential energy wells.

Now, Anderson, Seth Caliga and Cameron Straatsma have created an atomtronic battery that, in principle, could drive their transistor and other components. It consists of a gas of rubidium-87 trapped by magnetic fields in a long, thin cigar-shaped region. The BEC is created by cooling the atoms to an extremely low temperature so the atoms fall into the same low-energy quantum state. A repulsive energy barrier made from laser light is then swept across the trap from the right side to the centre, which pushes all of the atoms into the left half of the trap, leaving the right half empty (see figure). The energy barrier is then lowered in height to let atoms flow from the left half of the trap to the right half.

Chemical potential

Unlike conventional batteries, which are driven by an electrical potential, the atomtronic battery is driven by a chemical potential – which is related to the abundances of atoms in the left and right portions of the trap. “The atoms in the BEC repel each other,” explains Anderson. “They like to move away from each other, and given a circuit they can do so by causing a current of atoms.”

Anderson says that one possible use of the atomtronic battery is a temporally coherent source of matter waves – atoms that behave both as matter and waves. Such a source, he believes, could be combined with a matter-wave resonator to create an inertial sensor that could measure tiny accelerations. “Such circuitry would enable sensors that are competitive with current atom interferometers but be considerably smaller,” he says. The battery could also be used to apply quantum techniques to a problem known as “blind signal separation”, which aims to separate mixed signals from a number of different sources.

Anderson is also keen to demonstrate the quantum behaviour of his team’s atomtronic transistor. “This requires atomic temperatures that are in the range of 50 nK or so”. While colder temperatures have been achieved in laboratories, Anderson says such a demonstration involves significant technical challenges.

The atomtronic battery is described in New Journal of Physics.

Flash Physics: How single atoms conduct heat, prosthetic senses arm motion, 3D printer mimics plant porosity

Single gold atoms conduct heat like a metal

Single atoms of gold conduct heat according to the same physical law as larger pieces of the metal. That is the conclusion of researchers at IBM Research in Zurich, Switzerland, who have confirmed that the Wiedemann–Franz law applies to thermal contacts comprising just one gold atom. Dissipating heat in electronic circuits is becoming more difficult as devices become smaller and operate at higher frequencies, and therefore it is crucial to understand how heat is conducted along atomic-scale connections. The majority of heat transfer in a metal is done by the conduction electrons, which means that the thermal conductance of a metal is proportional to its electrical conductance – the Wiedemann–Franz law. While this law holds for bulk metals, it has proven difficult to confirm that it applies to nanometre- and atomic-scale structures. Making such measurements is particularly tricky for single-atom contacts because the electrical conductance is quantized. Now, Nico Mosso, Bernd Gotsmann and colleagues have addressed these challenges using a scanning tunnelling microscope (STM) with an atomically sharp gold tip that is brought into contact with a heated gold surface. Writing in Nature Nanotechnology, the researchers describe how they measured the thermal and electrical conductance of the tip as it was placed in thousands of different locations on the surface. While the conductances were different in different locations, the relationship between the two values obeyed the Wiedemann–Franz law. The measurement is also the first to make a direct link between quantized electrical conductance and quantized thermal conductance. The team now plans to use the set-up to measure the effect of lattice vibrations on heat conduction in tiny connections.

Robotic prosthetic senses phantom arm movements

The robotic prosthetic arm is moved by nerve signals detected by sensor device. (Courtesy: Imperial College London)

A new prosthetic arm could give amputees a full range of hand and arm function by detecting nerve signals. An international team has developed a sensor that can detect electrical signals from the nervous system and then interpret the signals to move a prosthetic arm. Currently available robotic prosthetics are controlled by movements in the remaining muscles. These remnant muscles are often damaged, which limits the prosthetics to simple grasp commands. The study in Nature Biomedical Engineering gets around this problem by focusing on the nervous system rather than muscles. The researchers, led by Dario Farina of Imperial College London in the UK, worked with six volunteers who had amputations from either the shoulder or just above the elbow. The volunteers had surgery to re-route nerves from the peripheral nervous system (nerves outside of the spine and brain) that would normally connect with the arm and hand. The nerves were instead directed to healthy muscles either in the bicep or chest depending on the amputation. A sensor patch made of high-density, flexible electrode grids then detects electrical signals from the re-routed nerve cells. The team decoded and mapped the signals using computer models and then compared them with those in healthy patients. As a result, they were able to program the prosthetic to respond to specific signals that were triggered by the patient thinking about phantom arm and hand commands. Although the work needs further refinements and clinical trials, the study is a proof-of-concept and the scientists hope that the robotic prosthetic will be on the market within three years, and they will be able to offer full movement to amputees.

3D printed structure mimics plant porosity

Close-up image showing the microporous structure within the node of the 3D printed triangular honeycomb — Holey walls: the microporous structure within the walls of a 3D printed honeycomb. (Courtesy: James Weaver/Wyss Institute)

A new 3D printed material takes inspiration from plant structures. By using ceramic foam ink, scientists at Harvard University and Massachusetts Institute of Technology (MIT) in the US have developed a method of printing 3D structures with both macro- and microscale structures. In nature, there are many extraordinary materials that have similar structures. Grass, for example, has a hollow tubular macrostructure with a porous microstructure. This means the plant can recover after compression and support its own weight. Jennifer Lewis and team looked to mimic this architecture to create strong, lightweight materials. Using a ceramic foam ink containing alumina particles, water and air, they printed a triangular honeycomb structure that had microporous walls. The ink and printed structure were both tested and tuned to optimize density and stiffness. Other foam inks can be made from polymers and metals, and the resulting lightweight material could be used for thermal insulation or tissue scaffolds. The work is presented in Proceedings of the Natural Academy of Science.

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 and atomtronic battery.

Water evaporation generates electrical energy

An electric power supply driven by water evaporating from a carbon nanomaterial has been unveiled by researchers in China. Their device is about 2.5 cm long and can create a voltage of about 1.5 V – on par with a standard AA battery. While the power supply only delivers a few hundred nanoamps, the team connected several devices together to run a liquid-crystal display. With further improvements, the researchers say, the device could be used to run sterilization equipment and to purify or desalinate water in warm regions of the world.

The power supply has been built by a team led by Wanlin Guo at Nanjing University and Jun Zhou at Huazhong University. It involved depositing multi-walled carbon nanotubes (MWCNTs) onto a quartz substrate to create two electrodes. The substrate is about 25 mm long and the 2 mm electrodes are positioned at each end. Carbon black – tiny particles of carbon about 20 nm in diameter – was then deposited, covering the substrate to a thickness of about 70 µm. Copper wires were then attached to each electrode and a circuit was completed via a voltmeter.

Dunked in water

One end of the device is placed in a beaker of deionized water so that the bottom few millimetres of the device are immersed. Capillary action draws water up the previously dry portion of the device, reaching a maximum distance of about 20 mm from the wet end in about 1 h. As the water rises through the device, the voltage across the electrodes increases, reaching a maximum value of about 1 V in 1 h.

When the device and beaker were placed in an enclosed environment from which water vapour cannot escape, the voltage dropped to zero in about 15 min – and recovered quickly when ventilation was provided. Air flow, which is known to boost evaporation, increased the voltage on the device up to 1.5 V. An increase in ambient humidity, on the other hand, lowered the voltage by inhibiting evaporation. Taken together, say the researchers, these observations confirm that evaporation is driving the operation of the device.

Streaming potential

An infrared spectroscopy study of the device suggests that electrical energy is created via a streaming potential. This is an electrochemical process that occurs when an electrolyte is driven by a pressure gradient through a channel or pore.

The team then connected four of their devices in series to create a power source that can deliver about 380 nA at 4.8 V – which was enough to drive a liquid-crystal display. The team says that the performance of the device could be enhanced by optimizing the streaming and evaporation processes.

The research is reported in Nature Nanotechnology.

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Nuclear diamonds: the ultimate long-life battery?

Flash Physics: Circuits survive on Venus, electronics powered by stomach acid, Israel tops global R&D spend

Integrated circuits smash survival record in Venusian atmosphere