The researchers (left to right): PhD student and first author Daseuli Yu and senior authors Byung Ouk Park and Won Do Heo.
Korean researchers have used light to control the binding of two separate and inactive antibody fragments and generate a specific, timely immune response to antigens. The platform that they created could help develop new therapies for cancer or autoimmune diseases (Nat. Methods. 10.1038/s41592-019-0592-7).
When a pathogen such as a bacteria or virus enters the human body, the immune system reacts by creating antibodies to identify the intruder and kickstart the chemical process that leads to its neutralization. With their Y shape, antibodies bind to a specific antigen and alert nearby phagocytes to the presence of an invader that needs to be eliminated.
Making antibodies more selective and efficient at detecting antigens has been a key research goal for developing new cancer or autoimmune therapies over the last three decades. Such antibodies, which have been engineered to generate a better and immediate immune response against their target antigens, are known as therapeutic antibodies. For example, the CAR T-cell cancer therapy that garnered a lot of attention following the 2018 Nobel Prize in Medicine associates a tumour-detecting antibody with cancer-killing T cells to create a “living drug” that can fight off tumours.
But for all their advantages, therapeutic antibodies are limited by our ability to control them. Their expression and regulation can be chemically induced, but the ability to precisely fine-tune their activity when and where needed has remained so far elusive, preventing the control of an antibody’s function within a living cell.
A one-in-all platform
A team led by Won Do Heo and Byung Ouk Park, from the Institute for Basic Science and Korean Advanced Institute of Science and Technology in South Korea, has now managed to achieve this control, by using a split–rejoin technique. Briefly, the researchers injected antibodies as two inactive split fragments (two separate branches of the Y shape) and used blue light to stimulate a reaction that led to linking of the branches and consequently, activation of their defensive function. They called the antibodies generated in this way “optogenetically activated intracellular antibody”, or “optobodies”.
As photoreceptors in GFP (nMagHigh1 and pMagHigh1) are triggered by blue light, split GFP nanobody fragments, which were roaming freely in the cell, reassemble. These now whole activated GFP nanobodies move toward their target proteins. (Courtesy: Institute for Basic Science)
The researchers first optimized their platform for insertion of binding domains. They tested it on two antibody fragments selected for their high target-specificity and stability: a single-chain variable fragment (scFv) and a single-domain antibody (a so-called nanobody). They first identified in a green fluorescent protein (GFP) nanobody the sites that required optical stimulation to spur the reassembling of the antibodies, and then compared the mitochondrial activities of the optobodies with similar, unmanipulated, antibodies.
While each separated fragment of the antibody did not display much mitochondrial activity, the optobody generated by linking the two branches displayed similar expression patterns to the original antibody. This finding indicates that there is no functional difference between optobodies and the natural antibody they are replicating.
Towards future breakthroughs?
Finally, the researchers tested whether the platform could generate optobodies targeting specific cells to disrupt pathway signalling. They administered novel nanobody fragments to cells derived from mouse and human embryos and monitored the ability of the optobodies to inhibit specific target endogenous proteins in these living cells. The team paid close attention to the cell movement and receptor signalling, two characteristics of pathogen expression. All of the optobodies studied bound to their target proteins and induced a reduction in cell movement, along with a significant reduction of signalling transduction.
“Our optobody system is a great tool to study the role of endogenous proteins in living cells and animals, and also shows great clinical promise for therapeutic strategies in the future,” says Heo. This could prove all the more interesting because the trigger source is not limited to blue light – other wavelengths such as near-infrared light could provide similar results with a different pool of antibodies. By offering more precise control of target protein activity, both spatially and temporally, the technique could eventually lead to the design of inducible “living” drugs for conditions where current therapies remain ineffective.
Quantum dots made of molecular graphene containing pentagon-shaped defects could form the basis of a new generation of quantum sensors. This is the finding of researchers in the UK and Germany who made the dots, or “graphenoids”, using a bottom-up chemical process rather than the top-down methods usually employed to create such nanostructures. The researchers say that such graphenoids could be employed in carbon-based devices that exploit quantum-mechanical effects to sense their environment.
Quantum technologies rely on manipulating the quantum properties of charges, spins or photons. Quantum spins in material defects such as nitrogen-vacancy (NV) centres in diamond are a popular platform for this work, but defects in other carbon materials – including graphene, a one-dimensional sheet of carbon atoms arranged in a hexagonal honeycomb lattice – also show promise.
Researchers have explored various ways of introducing spin defects into carbon nanomaterials, including encasing heteroatoms inside fullerenes, confining electrons in carbon nanotubes and functionalizing carbon nanoribbons. However, whereas the position of NV centres can be controlled with atomic precision, it has proved more difficult to control the locations of other carbon-based point defects. Indeed, researchers only managed to do so quite recently by introducing organic molecules with heptagonal ring structures at specific positions into graphene.
Bottom-up approach
A team of researchers led by Lapo Bogani at Oxford University in the UK have built on this work by introducing a saddle-shaped organic molecule into the hexagonal lattice of graphene. They chose this molecule – a “radicaloid” known as diindeno-fused bischrysen – because it incompletely hydrogenates in the final processing step, producing open-pentagonal-shell monoradical species that can act as defects.
In the past, graphene nanoribbons and other defect-bearing structures could only be obtained by starting with an advanced structure and modifying it, for example by making carbon nanotubes and then unzipping them. These top-down techniques invariably produced structures with undefined edges and uncontrollable defects, Bogani explains. In contrast, he and his team synthesized their diindeno-fused bischrysen from 11,11′- dibromo-5,5′-bichrysene in a five-step bottom-up chemical process that starts with small molecular precursors and builds up the final molecule.
The researchers checked every stage of this process with high-precision chemical characterization techniques, including mass spectroscopy and nuclear magnetic resonance (NMR). This enabled them to accurately determine the position of the pentagonal defects in the honeycomb lattice of graphene.
Long coherence time
The researchers report that when they put the spins of the resulting defects into a quantum superposition, the superposition remained coherent for up to 100 µs. Long coherence times are of paramount importance for quantum operations, and Bogani says that the robustness of the superposition in their system is due to low quantum noise from the nuclear spins in the molecule, as well as a low intrinsic spin-orbit coupling since the only elements in the structure are carbon and hydrogen.
The team, which includes researchers from Technische Universität Dresden and the Max Planck Institut für Polymerforschung, say that they will now be probing the quantum properties of their defects at room temperature by introducing the organic molecule they synthesized into matrices of solid systems such as liquid crystals or porous metal-organic frameworks. According to Bogani, possible applications include spintronics and optoelectronics devices as well as biological sensors.
“Our work straddles both quantum physics and synthetic chemistry and it paves the way to quantum manipulation of magnetic graphene-based structures in the future,” he tells Physics World.
Full details of the research are reported in Science.
Invisible forces: In the 19th century, “psychic” phenomena were taken seriously by many scientists. (Courtesy: iStock/VeraPetruk)
One day at the end of the 1980s, I saw conjuror James Randi stop by at the Nature office and read people’s minds. His sketches of what an editor was thinking – after picking a random word from a random page in a book on the shelves – resembled those presented by British physicist Arthur Chattock as examples of telepathy in the Journal of the Society for Psychical Research in 1897–1898. Chattock was one of many physicists inspired to investigate “psychic” phenomena at the time, thanks to the work of their distinguished peer, Oliver Lodge.
Randi was not, of course, reading minds. He made his name debunking “psychics” such as Uri Geller, who claimed to have paranormal powers such as telepathy and telekinesis. Randi would reproduce such feats while openly admitting that he was using nothing but stage conjuring techniques (although he would not reveal what they were). As Richard Noakes explains in his new book, Physics and Psychics: the Occult and the Sciences in Modern Britain, this same pattern could be found in the late 19th century: professional magicians of the Victorian theatre such as John Nevil Maskelyne often challenged the claims made by psychics, mediums and spiritualists by repeating their tricks using stage magic.
You might expect such exposure of fraud to have been as welcomed by the scientists of the time as Randi’s exploits have been in the modern day. But while many 19th-century scientists were sceptical of the bangs, levitating tables and spirit manifestations of Victorian séances, the prevailing view was that of people like chemist and entrepreneur William Crookes, electrical engineer Cromwell Varley, and Lodge himself, who believed that the task of science was to weed out the fraudsters so that we might better understand genuine psychic influences.
It has been common to regard Lodge and Crookes as anomalies. They were certainly scientific eminences – both had knighthoods and strings of awards for their work – but were nonetheless credulous individuals. Yet Noakes shows that an interest in psychical phenomena was shared by many prominent physicists of the late Victorian and Edwardian eras, including J J Thomson, Lord Rayleigh, James Clerk Maxwell, Gabriel Stokes, Francis Aston, and Pierre and Marie Curie. A historian at the University of Exeter, Noakes has been excavating this seam for several years, and Physics and Psychics is the rich, scholarly and long-awaited culmination of his efforts.
In the late 18th century, it seemed as though science would be a bulwark against the mystics and charlatans. A 1784 French commission, which included Antoine Lavoisier and Benjamin Franklin, was charged with assessing the claims of the German physician Franz Anton Mesmer that he could manipulate a force called “animal magnetism” for medical and paranormal ends. The commission concluded that there was nothing in it. And in 1853 Michael Faraday dismissed the craze for “table turning” (a type of séance) as a delusion produced by involuntary motions.
Yet as the enthusiasm for spiritualism, theosophy and other mystical movements gathered pace in the latter half of that century, scientists – and especially physicists – increasingly lent their cautious support. It’s not entirely clear why this was so, but three key factors were likely at play. First, the secularization and materialism of scientific thought left devout Christians such as Maxwell and Rayleigh uneasy. They began to seek ways to rescue articles of faith, such as the immortal soul, from the strictures of physical law.
Second, late-19th-century physics increasingly revealed invisible forces, emanations and influences: electromagnetic waves (studied by Maxwell and Lodge), cathode rays (Thomson and Crookes), X-rays and radioactivity (the Curies). These developments in science itself left its proponents ever less sure about what was, and was not, physically possible. The ether, thought to be the carrier of Maxwell’s waves, was widely suspected of being a “bridge between worlds”, capable of transmitting information from some unseen realm (where perhaps tenuous but intelligent beings existed) to our mundane sphere.
The third factor was new telecommunications technologies – such as the telegraph (which Varley helped develop) and the radio waves discovered by Heinrich Hertz in 1887 and soon used for transatlantic messaging. Together, they showed that it really was possible to transmit “voices” invisibly and wirelessly over great distances. If you could send them between London and New York, why not between the living and the dead?
These technologies were enlisted by physical scientists keen to study psychical effects. Crookes, for examples, hooked up people in séances to electrical circuits, so as to spot if the connection was broken as the medium sneaked off to dress as a “spirit”. He developed the radiometer – a tiny windmill encased in a vacuum chamber – as a device for sensing delicate psychic forces; it ultimately became a means to allegedly demonstrate the radiation pressure of light. The duty of science, Crookes wrote in 1870, was to examine these phenomena either to “inform their genuineness or to explain the delusions of the honest and to expose the tricks of deceivers”. Such scientific testing was central to the mission of the Society for Psychical Research, formed in the early 1880s by physicist William Barrett and others. The society still exists; its president from 2000 to 2004 was astrophysicist Bernard Carr.
The interest of physicists in psychical phenomena began to wane only in the 1920s – not so much because they all became firm sceptics but because the authority to make scientific pronouncements in the area was wrested from the physical sciences by the growing discipline of psychology. Noakes argues that, even if there was plenty of credulity involved in the way, say, Crookes was taken in by charismatic mediums, we should be wary of looking back at this episode and asking how all these first-class scientists could have been so foolish. Their psychical interests “were of a piece with the scientific and technological enterprises for which our protagonists are justly remembered”, he writes.
What’s more, we need to abandon the naive notion that advances in science and technology inexorably relegate such ideas to the dustbin. On the contrary, they create new places for them to reside: the ether, radio waves, quantum nonlocality, the Internet, dark energy. Brain-imaging methods are now making a kind of rudimentary mind-reading possible, and talk of “mind downloading” resurrects ideas about immortality and the transmigration of souls. The deeper question is why these ideas are so tenacious – and what, if anything, is worth salvaging from them.
Miguel Wattson is an electric eel (Electrophorus electricus) who lives in the Rivers of the World gallery at the Tennessee Aquarium in Chattanooga, US. The eel is best known for his tweeting ability under the Twitter handle @EelectricMiguel (although aquarium staff write his messages, which are triggered by the electrical pulses that Miguel emits while roaming around his tank).
Now workers at the aquarium have made Miguel the conductor of a Christmas tree that resides next to his tank. Gadgets in the tank pick up the electrical pulses and then an amplifier converts them into a stream of “pops” that trigger the lights on the Christmas tree. The brightness of the lights then depends on the strength of the pulse. You can see the effect for yourself in the stunning video above.
Is it worth tapping a can of beer or fizzy pop before opening to stop liquid from squirting out? That vexing question has now been answered by researchers in Denmark who studied “liquid leakage” from 1000 standard 330 ml cans (arXiv:1912.01999).
They randomly assigned the cans into four groups: unshaken/untapped; unshaken/tapped; shaken/untapped; and shaken/tapped. Tapping consisted of the researchers knocking the side of the can three times with a single finger while shaking involved jolting a can for two minutes. After recording the mass of each can before and after opening, they found that for both shaken and unshaken cans there was no statistically significant difference in the amount of liquid lost when tapped or not.
“The only apparent remedy to avoid liquid loss is to wait for bubbles to settle before opening the can,” they write. Sound obvious, but as the cans were provided by Carlsberg Breweries A/S, it is probably the best experiment in the world.
Finally, Brooke Kidner, a linguistics PhD student at the University of Southern California, has analysed hundreds of burps in the hit-TV series Rick and Morty to see if there is any “sub-textual” speech in mad scientist Rick Sanchez’s frequent gassing.
Kidner discovered that the burps rumble at a relatively low frequency of 300 Hz, but that the burps weren’t really burps at all but some other kind of “paralinguistic” sound such as the actor running out of air. Kidner presented her findings this week at the 178th Meeting of the Acoustical Society of America held in San Diego.
Human heart cells exposed to microgravity show surprisingly quick changes in function and gene expression, but largely return to normal when back on Earth, say researchers in the US. The team compared the RNA, morphology and behaviour of two sets of cardiac muscle cells in vitro, one of which spent more than five weeks onboard the International Space Station (ISS). Further experiments on 3D cultures and more complex tissue structures could eventually lead to treatments for a range of conditions suffered by astronauts during long space missions.
National space agencies and commercial companies share the goal of sending humans to Mars in the next decade or two. Barring a revolution in propulsion technologies, this will almost certainly involve astronauts spending many months in weightless conditions, causing physiological changes such as bone-density loss, muscular atrophy and decreased heart function. Despite decades of experience gained on the ISS and its predecessors, how these changes play out at the cellular level is still relatively unknown.
To help fill this knowledge gap, Alexa Wnorowski and Arun Sharma, at Stanford University School of Medicine, and colleagues used stem cells from three individuals to generate human cardiomyocytes – heart muscle cells that contract to give the organ its beat. They split each of the three cell lines into two 2D cultures, cultivating one set on the ground while the other was launched into space (Stem Cell Reports 10.1016/j.stemcr.2019.10.006).
During the samples’ 5.5 weeks on the ISS, astronaut and co-author Kathleen Rubins, of NASA Johnson Space Center, observed the cells’ contraction dynamics using video microscopy. After the cells were returned to Earth, the researchers used phase-contrast microscopy and immunofluorescence microscopy to measure the cell morphology. Equivalent observations on the ground-based cells revealed no significant differences in shape and structure between the two sets of cultures. However, those in orbit beat less regularly and contracted and relaxed more slowly, which the researchers attribute to changes in the way calcium was cycled within the cells.
The researchers also harvested cells during and after the mission so that their transcriptome could be sequenced. The transcriptome is the cell’s set of RNA molecules, and indicates which genes are active at a given time. More than 3000 genes showed differences in their level of expression between the ground and flight cultures, with changes clustered mainly around those that regulate cellular metabolism.
These changes in the transcriptome did not include genes related to calcium cycling, so the researchers think that the altered contraction dynamics seen in the spaceborne cells were a non-genetic response to the change in their environment.
“There are known pressure- and tension-sensing proteins that enable cells to sense and respond to their environment. This may be responsible for some of the cellular responses that we observed,” says Joseph Wu, the team’s leader, and director of Stanford Cardiovascular Institute.
Whether it was just microgravity that the cells were responding to is not certain, however, as the researchers note that the ISS samples experienced additional forces during launch and re-entry, as well as a possible increase in radiation during their time in orbit. They say that future experiments will need to include a spaceborne control group that is cultured in a centrifuge to simulate surface gravity.
Ten days after the cultures returned to Earth, the researchers assessed the cells’ behaviour again, and took further samples for RNA analysis. By this time, most of the differences in gene expression between the two groups had faded away, but about 1000 remained – as did the functional changes related to calcium cycling. Wnorowski, Sharma and colleagues cannot say whether the cells would have returned fully to their pre-flight state given a longer recovery period.
As above, so below
The study represents only the first investigation into the effects of microgravity on human cardiac cells, and will be followed by experiments involving engineered human heart tissues consisting of multiple cell types. Wu thinks that the insights that these studies yield could find use in space and back on Earth.
“The ‘easy’ way to keep the heart and other muscles of the body as healthy as possible is for astronauts to exercise regularly and intensely, but perhaps there could be therapeutic means to prevent this cardiac remodelling that occurs in orbit,” says Wu. “Such a potential ‘heart strengthening’ therapy could also have applications for individuals experiencing heart failure on the ground.”
Taking flight: Makani’s kite, tethered to a buoy during offshore tests in Norway. (Courtesy: Makani)
The island of Curacao bears all the hallmarks of a tropical paradise. A city-sized scrap of land in the Lesser Antilles, it boasts sandy beaches, coral reefs and an undersea cliff called “the blue edge” that attracts scuba divers from all over the world. The trade winds that once brought sailing ships (and, unhappily, slave traders) to this former Dutch colony also endow it with a balmy climate. Temperatures in December hover around 27 °C, and the sun shines, on average, 270 days a year.
Look closer, though, and Curacao has its challenges. Though richer than most of its Caribbean neighbours, and less isolated than many, the cost of living here is high. Curacao’s 150,000 residents import a lot of essential goods, including the fossil fuels that generate much of their electricity. Dependence on imported fuel is ironic as well as expensive. Thanks to a huge oil refinery near its main harbour, Curacao had, in 2014, the second-highest carbon emissions per capita of any country in the world – not a great look for a low-lying island threatened by rising sea levels.
To Johannes Peschel, the answer to Curacao’s carbon quandary lies in its greatest natural resource: the wind. Curacao was an early adopter of wind power, and by 2017 commercial wind farms were producing 30% of its energy. But Peschel, a German entrepreneur with a bushy beard and a surfer’s laid-back enthusiasm, wants to push that figure higher, and his plans do not involve adding more turbines to the coastline. Instead, he and his local partners are pinning their hopes on a technology that is both centuries old and entirely new: giant, tethered kites that generate energy as they soar through the blue Caribbean sky.
Let’s go fly a kite
For Peschel and others in the small but growing airborne wind energy (AWE) community, the future of wind power looks nothing like the familiar three-bladed turbines scattered across the hills and coasts of Europe. Researchers in this nascent field are working on a dizzying array of devices, including kites, wings, drones and even a set of spinning, sky-borne hoops that are being developed by a Scottish firm called Windswept and Interesting. In all cases, the goal is to harness high-altitude wind in a way that is cheaper and more flexible than erecting lofty columns of steel and concrete.
Different approaches: Several types of airborne wind energy systems are being developed, including Kitepower’s kites (top) and TwingTec’s drone (bottom). (Courtesy: Kitepower; TwingTec)
To residents of islands like Curacao, as well as communities in areas without conventional electrical grids, AWE offers substantial advantages. Peschel – whose company Kitepower spun out of a research group at TU Delft in the Netherlands – notes that its biggest kite, with an area of 100 m2 and a generating capacity of 100 kW, fits into a large surf bag and can be launched by two people in 20 minutes. Fixed-wing AWE systems are bulkier, but not by much. Rolf Luchsinger, who leads a Swiss AWE firm called TwingTec, drew appreciative murmurs at a recent industry conference in Glasgow, UK, when he showed a photo of TwingTec’s drone and ground station (total mass: 1 tonne) sitting next to a standard turbine (20 tonnes). The two systems, Luchsinger observed, produce comparable amounts of energy – but only TwingTec’s will fit in a shipping container.
TwingTec, Kitepower and a clutch of similarly named companies (EnerKite, Kitemill, SkySails Power, Windlift and so on) are pursuing the same path to market that conventional renewables followed a generation ago. By offering small, 10–100 kW systems to customers in remote locations – where costs per kWhr are high and the main alternatives are dirty, noisy diesel generators – they aim to refine their technology and prove its worth before scaling it up.
Airborne wind energy systems are far less bulky than traditional wind turbines. (Courtesy: TwingTec)
Other firms are targeting large-scale power generation from the start. A second Netherlands-based start-up, Ampyx Power, is developing a tethered aircraft that can take off and land on floating platforms far out to sea. Its newest model has a rated power of 300 kW, and chief executive Richard Ruiterkamp says the company will begin flying it at a purpose-built test site in County Mayo, Ireland, sometime next year. In August the US-based firm Makani tested its 600 kW kite in a Norwegian fjord, collecting reams of data on how the kite-tether-buoy system (see photo above) behaves under real-world conditions. Both companies envision a future where large, multi-kite farms deliver hundreds of megawatts of low-carbon energy to the grid. “I’m really passionate about bringing renewable energy to more and more people around the globe,” says Doug McLeod, Makani’s technical programme manager. The August test was, he says, “an exciting moment”.
Up to the highest height
Kites have been used to pull loads since ancient times, but their power-generating potential was not fully appreciated until relatively recently. During the oil crisis of the late 1970s, Miles Loyd, an engineer at Lawrence Livermore National Laboratory in the US, began studying a phenomenon that novice kite-fliers learn the hard way: a kite moving perpendicular to the wind pulls much harder than a stationary kite with the wind behind it. This is because the kite’s aerodynamic lift force scales with the square of its apparent airspeed. In cross-wind flight, this apparent airspeed can be easily an order of magnitude higher than the wind speed relative to the ground.
Loyd’s contribution was to calculate that a kite flown in fast loops across the wind would produce enough lift not only to support itself, but also to generate a useful amount of power – hundreds of times more power, in fact, than a kite in static flight. Using realistic numbers for wing area, wind speed and lift-to-drag ratio, Loyd estimated that a single “crosswind” kite could produce as much as 45 MW. This was far higher than the turbines of Loyd’s day, and it remains competitive even now. As of 2019 the world’s most powerful commercial wind turbine, the Vestas V164, maxes out at 8.8 MW.
Falling oil prices took some of the shine off Loyd’s ideas, and a few of his approximations would be right at home amid the frictionless surfaces and spherical cows of introductory physics courses. In estimating the maximum power output, Loyd ignored both the mass of the kite-tether system and the aerodynamic drag on the tether. Neither approximation is valid, and the second is particularly egregious. Luchsinger, a physicist by training, says that for small craft like TwingTec’s drone, the drag on the tether is greater than the drag on the wing. Even so, Loyd’s work remains influential. Most AWE companies are building kites that fly across the wind and generate electricity using one of the two methods Loyd proposed (see box).
Send it soaring
Optimal pattern: Flight path of the TU Delft pumping kite power system computed with a dynamic system model (kite not to scale). From Uwe Fechner 2016 “A Methodology for the Design of Kite-Power Control Systems” Delft University of Technology.
In his seminal paper (J. Energy4 106), Miles Loyd proposed two ways of making crosswind kites do useful work. One method – which he termed “lift mode” – is to use the kite’s aerodynamic lift to pull a load on the ground, for example by winding the tether around a drum, allowing it to unspool, and using the drum’s rotation to drive an electric generator. The alternative – known as “drag mode” – is to attach turbines to the crosswind kite, generate electricity onboard and transmit it to the ground via a conducting tether.
Kites that operate in lift mode must periodically lose lift and be reeled in while the tether is slack. In effect, these kites act like giant, slow-motion, airborne yo-yos, generating a lot of energy on their way out and losing a little on their way in. (Kitepower’s Roland Schmehl, more prosaically, likens the “pumping” process to the thermodynamic cycle of a reciprocating engine.) The crosswind devices at (among others) Ampyx Power, EnerKite, Kitepower, Kitemill, SkySails Power and TwingTec all produce electricity in this fashion.
AWE systems that operate in drag mode fly in less complex patterns, and their onboard turbines can power motors that enable vertical take-off and landing. Makani’s kite generates energy as it flies in circles across the wind, and hovers before landing on a floating buoy called Havdrage-1 (the name means both “ocean kite” and “ocean dragon” in Norwegian). Another firm, Windlift, is developing a drag-mode AWE system with funding from the US military. Its chief executive, Rob Creighton, notes that drag-mode devices can remain aloft in powered flight if the wind slackens – a big advantage for customers who may not want to stop other activities to land a kite at short notice. The disadvantage is that conductive tethers have larger diameters, and so experience more drag.
If the power-generating potential of crosswind flying helped get AWE off the ground, other advantages may prove just as important in keeping it aloft. A key part of the technology’s appeal is that kites can harvest wind energy that conventional turbines cannot. A typical 1.5 MW turbine stands 100 m tall, and its net capacity factor – the actual energy produced, divided by the maximum possible – is usually less than 50% due to the intermittent nature of wind. Kites, in contrast, can fly at altitudes of up to 500 m, where winds are stronger and more consistent.
The greatest attraction of AWE systems, though, is their low mass. An energy kite is a turbine stripped back to its power-generating essence, with no need for weighty components such as a base and a tower. Kitepower’s co-founder Roland Schmehl, a researcher at TU Delft, compares it to a set of flying rotor tips. The drastic reduction in mass should, in principle, reduce costs, making wind energy more likely to be exploited. According to Cedric Philibert, a renewable-energy expert at the International Energy Agency (IEA), conventional wind turbines in European waters could generate 2600–6000 TWhr per year, or 80–180% of current EU demand – but only at a cost of €55–70/MWhr. The current price in France, Philibert notes, is €44/MWhr.
AWE advocates say that their devices will make it possible to harness much more of the Earth’s wind energy. A combined solar and AWE farm, where kites cast tiny, transient shadows as they circle high above the photovoltaic panels, is one possibility. Kitepower’s Curacao project, in which the company plans to operate three to five 100 kW kites on an existing conventional wind farm, is another. The most tantalizing prospect, though, is that AWE could unlock the “stranded resource” of wind in off-shore locations where the water is too deep to fix conventional turbine towers to the ocean floor. Compared to a floating turbine, a floating AWE platform would need a much less massive counterbalance to keep it upright in stormy seas.
Turbulence ahead
All these advantages come at a price, and Ruiterkamp of Ampyx Power sums it up well. “The threshold for getting a first series to work is way higher than in other areas of wind energy,” he told his colleagues in Glasgow. “We are working on intrinsically unstable systems. If something goes wrong, we are immediately in a situation that needs to be handled.”
With a device as complex as an energy kite, the list of things that can go wrong is extensive. In another talk at the Glasgow meeting, Kitemill technical manager Lode Carnel rattled off a litany of problems that his Norway-based team had overcome on their current, rigid-wing prototype. Weak links breaking. Electrical connectors not up to industrial standards. Tether and wing materials that proved too flimsy or heavy. Though minor in themselves, Carnel explained that these issues contribute to a vicious circle in which investors see AWE technology as immature, and thus not worth funding – meaning that companies struggle to get the days, weeks and months of flight experience they need to refine their systems.
It doesn’t help that most AWE devices, unlike turbines, need to land when wind conditions are poor. Landings and launches are hard to automate, and each one raises the risk of catastrophic failure. Lorenzo Fagiano – an associate professor at Italy’s Politecnico di Milano who did his PhD research on AWE – points out that even if an individual kite can fly for two days straight, a large-scale AWE farm with 300 such kites would still experience 54,000 take-off-and-landing events each year. “This phase has to be proven against any fault with an extremely high probability,” he warns.
In off-shore operations, the bar for safe launch and landing is even higher. Each contributing system must work in a remote and harsh environment, with minimal maintenance and generally without supervision. In this respect, the industry’s first offshore test was both an impressive milestone and a sign of how much work remains. Landing Makani’s kite on a moving buoy was, McLeod observes, “like trying to parallel park a car while the kerb is moving up and down and back and forth, and also rotating for good measure”. Although that landing was successful, the test ended with the loss of the kite.
Look out below
In a young industry with a new technology, such mishaps are inevitable. They are also the reason why AWE is, at present, confined to lightly populated areas. At the Glasgow conference, there was broad agreement among delegates that an accident – such as a kite colliding with an aircraft, or with a person on the ground – would harm the entire sector, regardless of which company was responsible. But the question of how to regulate AWE provoked a rare public dispute, centred on a question that members of this friendly, freewheeling community sometimes struggled to answer: just what are these strange new objects in the sky?
For Neal Rickner, Makani’s chief operations officer and a former F/A-18 pilot, the answer is simple. “We are talking about wind turbines, not aircraft,” he declared. “From a pilot’s point of view, you would not expect an energy kite to be in one part of the sky at one moment, and another part at the next.” A failure of a kite’s tether, Rickner argued, should be treated just like a failure in the blade of a conventional turbine. “We need to imagine a future where systems are highly reliable, and therefore operate under the same procedures as the [conventional wind] industry is using today,” he concluded.
Some of Rickner’s fellow panellists were less convinced. Michiel Kruijff, head of technology at Ampyx Power, explained that its kite stores energy on board so it can fly back to its platform if its tether breaks. That means it must follow aviation rules, although Kruijff said that Ampyx hopes to negotiate some adjustments. But in his view, even companies without these constraints need to face some facts. “We all acknowledge that we are primarily developing an energy-generation device,” he said. “But we cannot deny that there is an element in it that is not like a wind turbine.” Turning to Rickner, he asked rhetorically, “When you look at your beautiful system in the air, do you say, ‘Look how beautifully it is rotating’? Or do you say, ‘Look how beautifully it is flying’?”
The sky’s the limit: Energy kites fly at much lower altitudes than commercial aircraft, reducing the risk of collision. (Courtesy: Kitepower)
Semantic and regulatory disputes aside, questions about how to keep energy kites safe may prove easier to answer than questions about how to make them reliable enough for commercial operations. Asked to name the hardest problem in AWE, Ruth Marsh, who spent 15 years working in conventional wind energy before joining Makani as its product and system lead, looks thoughtful. “There are a lot of hard problems,” she says. Then Marsh – a former aeronautical engineer at NASA, and a rare veteran woman in a field that skews young and male – offers an analogy.
In solar panels, she says, structural and power-generation components are separate. They can be optimized independently. In conventional turbines, structure and power interact, so they must be optimized together. But energy kites have lots of moving parts, all of which must work optimally together for the system to perform at its peak. As the technology matures, Marsh suggests that the most important numbers to watch will be power production, net capacity factor and levelized cost of energy – hard, commercial measures that will, in the end, determine whether the AWE industry takes off.
Flying high and growing big
Over the next few years, AWE developers hope to fly their devices for longer periods, with less human intervention. Kitepower’s mini-AWE park in Curacao will operate automatically under the watchful but remote eyes of technicians in Delft, who will use sensor data to decide when to land the kite for maintenance and re-launch by a local ground crew. Another company, SkySails Power, has already deployed its kite as an auxiliary generator on a catamaran operated by an environmental charity, Race for Water. In 2020 it plans to offer commercial, ground-based “plug and play” AWE units of up to 500 kW.
For companies at this stage of development, the state-of-the-art is days or weeks of automated flying. The long-term goal, especially for off-shore applications, is to push that to months or even years of complete autonomy. It’s an ambitious target, and it isn’t clear when (if ever) it will be met. Fagiano points out that self-driving cars and robotic systems, which face analogous challenges, are getting billions of euros in funding. For AWE, he says, that level of support “may never be there”.
The physics behind airborne wind energy is sound, and it has a rare ability to capture the imagination
Still, the physics behind AWE is sound, and it has a rare ability to capture the imagination. “People like kites, and they like green energy,” says Joep Breuer, Kitepower’s technical manager. “It’s a very likeable technology.” By 2027 the IEA predicts that wind will be the number-one source of the EU’s energy, but even that will not be enough to meet stringent emissions targets. Alexander Bormann, the chief executive of EnerKite, concurs. “Some people think that airborne wind is crazy stuff,” he says. “You know what I think is crazy? Installing less capacity in renewable energy. We need to save gigatonnes of carbon dioxide today, not tomorrow. We need to fly high and grow big.”
This year, Physics World‘s Book of the Year award is celebrating its 10th anniversary. Indeed, 2019 marks a decade of excellence in popular-physics books, and suffice to say that this year’s shortlist reflects this. We’ve based our choices on the 42 books we’ve reviewed over the last 12 months in Physics World, picking our favourite 10 using the same three criteria – that the books must be well written, novel and scientifically interesting to physicists – that have been in place since we launched our Book of the Year award in 2009.
As is the case every year, picking one winner from 10 such interesting and varied books is a tough task, but keep your eyes peeled on 17 December, when we will reveal this year’s award-winning book, via the monthly Physics World Stories podcast. Meanwhile, why not listen to last week’s Physics World Weekly podcast, where past and present reviews editors look back over the 100 books that have featured on our shortlists for the past 10 years. And if you’d like to remind yourself of some past winners, here are a few of the previous years’ shortlists: 2018, 2017, 2016, 2015, 2014, 2013, 2012.
The shortlist for Physics World’s 2019 Book of the Year
The Moon: a History for the Future by Oliver Morton
As we celebrated the 50th anniversary of the Apollo Moon-landings, Oliver Morton’s book tells the story of our Moon, from its origin to its role in humanity’s history and future.
Underland: a Deep Time Journey by Robert Macfarlane
From dark matter to nuclear waste, Robert Macfarlane’s Underland will take you deep within the bowels of our planet, and our relationship with these hidden worlds.
On Tuesday 3 December the World Meteorological Organisation (WMO) released the provisional statement for its 2019 State of the Climate report. The full report will be published in March but it looks certain that 2019 will conclude the decade with the highest average global temperature since records began. WMO senior scientific officer Omar Baddour was the coordinator of the report and he speaks to science journalist James Dacey in Madrid at the UN Climate Change Conference (COP 25) .
Omar Baddour (left) and James Dacey
Baddour, who has an academic background in physics and maths, speaks about how to report is synthesised from the multitude of available data. He also explains how the annual report’s scope has expanded to consider the impacts of climate change on natural and human systems. Acknowledging that audiences are fatigued by constant gloomy news from climate scientists, Baddour argues that such detailed climate information will be essential in the transition to low carbon societies.
This week we chat about the first five breakthroughs on our list. These are a new technology for converting thoughts into speech; the first images of a black hole event horizon; the first detection of a “Marsquake”; the discovery of symmetry violation in charm mesons; and a “Little Big Coil” that created a record-breaking magnetic field.
The closest ever mission to the Sun has discovered dynamic structures in the solar wind that will help explain how this flux of charged particles is created and evolves as it travels out into space. The results are highly relevant here on Earth because the solar wind generates space weather including solar storms, which can damage power grids, communication networks and satellites.
NASA’s Parker Solar Probe launched in 2018 and has made measurements of the Sun from a distance of just 24 million km. This is less than half the distance between Mercury and the Sun.
The first results from the mission show bizarre S-shaped bends in the solar wind, which is a stream of energetic charged particles riding through the Solar System on magnetic field lines emanating from the Sun. There are two main components to the solar wind: the fast wind that appears to emanate from magnetic gaps in the Sun’s corona; and the slow wind, which is more of a puzzle.
Indeed, understanding how the particles in the solar wind are accelerated, and what role the heating of the corona (the Sun’s the million-degree-hot atmosphere) has in this, is the greatest mystery facing solar physicists.
Those S-shaped bends are a puzzle. They have been observed before, at greater distances from the Sun, but it was a surprise to find them so pronounced closer to the Sun.
“We have theories, but we don’t know for certain” what produces them, Christian tells Physics World. What the bends highlight is that the structure within the solar wind is imprinted upon it close to the Sun, where the solar wind is far more turbulent than it is as it passes Earth.
The connection between what happens in the Sun’s immediate environment with the dynamics of the solar wind has also been explored by Parker Solar Probe. In particular, small eruptions of plasma from magnetic instabilities on the Sun have been observed feeding the solar wind.
“The solar magnetic field is directly related to solar wind fluctuations,” says Russell Howard, who is the Principal Investigator on the mission’s Wide-field Imager for Solar Probe (WISPR) instrument. It seems that close to the Sun, it is disturbances in the Sun’s volatile magnetic field that governs the structure of the solar wind, whereas at greater distances, such a near Earth, the kinetic energy of the charged particles in the wind is able to dominate over magnetic field effects.
WISPR also found evidence for a dust-free zone near the Sun, which was first predicted 90 years ago by the American astronomy Henry Russell, of Hertzsprung–Russell diagram fame. This dust is cleared out from the environment near the Sun by heating that prompts the dust to evaporate, or radiation pressure blowing it away.
Rotational puzzle
The new results also show that, alongside the solar wind’s radial velocity, there’s also a rotational component that moves at between 35–50 km/s. As the Sun rotates, it creates magnetic tension in the corona and as magnetic fields twist up, plasma ends up being flung out into space. This had been expected, but its rotational velocity far exceeds the predictions. This proves to be a problem, because as the Sun throws off this material it gradually loses angular momentum that, over billions of years, slows its rotation, and the basics of this model have been applied to spin-down rates in other stars too. The fact that the rotational velocity component of the solar wind seems to be higher than expected challenges scientists’ understanding of how stars spin down.
Parker Solar Probe continues to edge closer to the Sun. As its orbit shrinks, it will eventually reach a perihelion distance of just 6.16 million km in 2024–25, where it will experience temperatures of nearly 1400 °C. A specially-designed, carbon-composite heat shield protects the spacecraft’s instruments as they face a solar intensity 475 times that which spacecraft orbiting the Earth experience.
Says Christian, “In these small structures are the keys to how the solar wind is accelerated, how the corona is heated, and how energetic particles are accelerated”.
The first observations are presented in four paper papers published in Nature.
