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Gigapixel camera pushes resolution limit

Researchers in the US have unveiled a 1 gigapixel camera, which has about five times as many pixels as today’s best professional digital cameras and nearly 100 times as many as a compact consumer camera. Moreover, the camera has a much smaller aperture than other gigapixel devices – meaning that, unlike other sensors, this latest camera pushes the fundamental resolution limit of optical devices. The team has also shown how the device could be used in several applications including surveillance, astronomy and environmental monitoring.

In the past, gigapixel images have be formed by stitching together 1000 or more megapixel images, or by scanning a sensor across a large-format image. Acquiring “snapshot” gigapixel images is trickier, but a few options exist or are in development. One of these is the 3.2 gigapixel digital camera that will sit within the Large Synoptic Survey Telescope (LSST), an optical device currently under construction in northern Chile.

Aperture effects

In theory, the smallest details resolvable by a lens are limited by diffraction, and the larger the lens – that is, the greater the aperture – the smaller the details it is possible to identify. A 1 mm aperture should be able to resolve about 1 megapixel, while a 1 cm aperture should be able to resolve 100 megapixels. The LSST, which will have an aperture of several metres, should be able to resolve not just images of gigapixels, but of terapixels.

In practice, however, large lenses struggle to reach their diffraction limit. One problem is that big lenses are more likely to suffer from aberrations, which smudge the focusing, particularly around the extremities. Lens designers get round this problem by introducing more lens elements and reducing the field of view. Nevertheless, these devices still generally fail to get close to the diffraction limit.

Pushing the diffraction limit

Now, David Brady of Duke University in North Carolina and colleagues claim to have created a high-resolution camera that approaches the diffraction limit. Known as AWARE-2, their camera has an aperture of just 1.6 cm yet offers a resolution of 1 gigapixel. For visible light, that is half way to the diffraction limit of 2 gigapixels.

AWARE-2 uses a “multiscale” design, where one spherical objective lens projects a coarse image onto a sphere. On this sphere, an array of 98 microcameras, each with a 14-megapixel sensor, refocuses and samples the image. “The design approach is directly analogous to the development of supercomputers using arrays of microprocessors,” says Brady. “We build supercameras using arrays of microcameras.”

Drop in price

The Brady group’s approach works because it replaces one big camera with a composite of tiny cameras, which are less prone to aberrations. It also means a cut in cost: the mobile-phone market has brought the cost of sensors down to about $1 per megapixel, which suggests cameras of the AWARE-2 design could one day cost just $1000 per gigapixel. Brady thinks it should be possible to manufacture cameras for less than $100,000 per gigapixel by 2013. “We hope that our systems will reach $10,000 per camera within 5 to 10 years,” he says.

However, not everyone is impressed. Engineer David Pollock of the University of Alabama in Huntsville believes the AWARE-2 camera suffers from “a lack of focal length”. Shorter focal lengths tend to have lower “f-numbers” – that is, wider relative apertures – resulting in less thermal noise. On the other hand, shorter focal lengths mean less magnification: the subjects recorded on the camera sensor appear very distant.

Minimum focal length

This is true of the AWARE-2 camera, which offers a very broad field of view of 120°. But Brady does not consider this feature a disadvantage. “In my experience, lens designers universally regard the ability to design to the minimum focal length possible as a positive thing,” he says.

“I would say that this debate gets to the heart of the innovator’s dilemma of the battle between good and excellent,” he adds. “Current high-pixel-count imagers for aerial photography and astronomy are very good systems and their designers are naturally hesitant to believe that a better approach is possible…It’s a fun battle to fight.”

The team has also shown how the camera could be used in a number of different applications. In one example, the camera acquired an image of a lake in North Carolina that was then analysed to determine how many swans were on the lake. In another example, details such as car licence-plate numbers and individual faces were picked out of a surveillance image.

The work is described in Nature.

Silicene pops out of the plane

Researchers in Japan say that they have made 2D honeycomb crystals of silicon that resemble the carbon-based material graphene. This is the second potential sighting of the material dubbed “silicene”; the other was reported in April by an independent group in Europe. The Japanese research suggests it may be relatively easy to alter the structure of silicene by changing the substrate on which it is grown – which could allow different versions of silicene to be produced with a range of useful electronic properties. However, not all scientists agree that this latest material is actually silicene.

Graphene is a honeycomb lattice of carbon just one atom thick and since its discovery in 2004 the material has proved to have a myriad of interesting and potentially useful properties. As well as being the material of choice in the electronics industry, silicon lies directly below carbon in the periodic table. The latter suggests that if silicon atoms were deposited in a layer on an appropriate surface, they could arrange themselves in a honeycomb lattice to make silicene – which would have properties similar to graphene.

Silicon on silver

This was first done by a team of researchers in Italy, Germany and France that included Paola de Padova of the Consiglio Nazionale delle Ricerche-ISM in Rome. De Padova and colleagues deposited silicon on a silver crystal and found the film to have the structural and electronic properties expected of silicene.

Now, a team in Japan led by Yukiko Yamada-Takamura of the Japan Advanced Institute of Science and Technology in Ishikawa say that it has created a modified form of silicene on a substrate of zirconium diboride. The crucial difference to the previous work is that while silver has a very similar lattice constant to that expected of silicene, the lattice constant of zirconium diboride is quite different. As a result, silicene grown on silver adopts a flat, graphene-like atomic configuration and has very similar properties to the carbon-based material. Silicene on zirconium diboride, on the other hand, has a distorted lattice structure.

It is this ability to distort the silicene lattice that appeals to Yamada-Takamura and colleagues. This is different to the structure of graphene, which is very stable. This stability is a problem because altering graphene’s structure could provide researchers with a way of creating an electronic band gap in the material – a development that would allow graphene to be used in a wide range of electronic applications.

Flexible on an atomic scale

The team describes silicene as being very “flexible” and says that it should be possible to manipulate its structure in ways that are virtually impossible with graphene. “You can roll a sheet of graphene or something like that,” explains Yamada-Takamura, “but what we mean by flexible is that silicene can be atomitistically flexible, so the atoms can be displaced out of the plane.” This buckling out of the plane leads to very different electronic properties and by depositing silicon on a variety of different substrates, the researchers believe it may be possible to produce a whole family of silicenes that offer a range of different electronic properties.

De Padova is impressed by this latest work, but is cautious about describing the new material as silicene. “I think the paper is interesting because there is, in principle, evidence for the growth of silicene on, for example, zirconium diboride and not only on silver.” She is reluctant, however, to endorse the researchers’ conclusion that their material is a modified form of silicene. She also has doubts about whether the work shows that the properties of silicene can be modified by epitaxial strain. She suggests instead that the substance produced on the surface of the zirconium diboride may not be silicene at all. Yamada-Takamura responded “that depends how you define silicene”.

The research is published in Physical Review Letters.

UK should lead on open-access publishing, says report

The UK should lead the way in transforming scientific publishing from a “reader pays” model to an “author pays” model. That is the main conclusion of a 140-page report released today by an independent working group of academics, publishers, librarians and representatives from learned societies. Led by the British sociologist Janet Finch, the 15-strong working group includes Steven Hall, managing director of IOP Publishing, which publishes physicsworld.com.

Commissioned by the UK government, the report notes that the Internet has had a profound impact on how scientists access peer-reviewed research papers, with nearly all articles now being available online. However, many journals are subscription based, which means that they can only be accessed by researchers working at institutions that have taken out a subscription or those who are willing to pay a one-off fee to access individual articles on a pay-per-view basis.

Some researchers therefore feel that subscription-based journals are preventing the results of government-funded research from being more widely disseminated, arguing that it should be freely accessible in the public domain – a view that the report describes as both “compelling” and “fundamentally unanswerable”. Proponents of this “open access” model say it would not only benefit researchers in smaller universities and poorer nations that cannot afford subscriptions, but also help inventors and small businesses by giving non-academics access to scientific and technical knowledge.

The challenge in making the transition to full open-access publishing will be to decide who should pay the not insubstantial cost of running peer-review systems, publishing the papers and maintaining and upgrading the complex online systems that underpin most modern journals. The Finch group has come down firmly in support of the “author pays” model, whereby scientists pay an article processing charge (APC) before a paper is published. This model is already used in part by a number of scientific publishers, including IOP Publishing, which has run New Journal of Physics in this way since it was launched in 1998 with the German Physical Society.

The report calls on UK research councils – which provide the bulk of public research funding – to “establish more effective and flexible arrangements to meet the cost of publishing in open-access and hybrid journals”. Based on an APC of about £1750, the group believes that a move to open access would cost the UK an additional £38m per year. The report also says that the UK government must spend an extra £10m per year to extend its current licences on reader-pays journals to provide wider access to this material in the higher-education and health sectors, with publishers also providing “walk in” access at public libraries at no charge.

A further £3–5m per year, the report argues, would need to be spent on open repositories of scientific reports that have not been subject to peer review. Such repositories, it suggests, could contain work done at a university or institute – or done UK-wide in a specific discipline. The report also cites a one-off transition cost of £5m, putting the total cost of the transition to full open access at about £50–60m per year. This, it says, is “modest” compared with the £10.4bn that the government spends every year on research and development in the UK.

One challenge facing the UK if it leads the move to open access is how to apportion APCs when research is published by an international collaboration that includes one or more UK-based scientists. According to the report, about 46% of papers met this criterion in 2010 and a clear policy would have to be put in place to decide who pays for what – and what to do if foreign funding agencies refuse to pay their share.

Response and reaction

David Willetts, the UK’s minister for universities and science, has welcomed the report, saying that it will shape the government’s forthcoming policy on open-access journals. “Opening up access to publicly funded research findings is a key commitment for this government,” he says. “Proposed initiatives such as providing access to findings for small companies and making peer-reviewed journals available free of charge at public libraries would foster innovation, drive growth and open up a new area of academic discovery.”

The response from the publishing industry has generally been positive. David Hoole, marketing director of Nature Publishing Group that publishes the Nature suite of journals, says that the company “welcomes the balanced approach of the Finch report, and its recognition of the need for a mixed economy, of licensing subscription content, self-archiving and open-access publication”. However, Hoole warns that the small number of papers published in highly selective journals such as Nature will require APCs higher than those acknowledged in the report.

Timothy Gowers, a mathematician at the University of Cambridge who is involved in a boycott of the commercial publisher Elsevier, told physicsworld.com that while he welcomes the general direction suggested by the report, he does not think it sufficiently acknowledges the “very large” profits that he says publishers make. “The report recommends moving to a more open system, which I strongly support,” says Gowers. “But I would have liked to have seen a bolder report that also recommended taking steps to move to a cheaper system that covers the costs of publishers but significantly reduces their profits.”

Any move to open access will also affect UK-based learned societies such as the Royal Society, the Institute of Physics and the Royal Society of Chemistry, all of which publish journals on a not-for-profit basis. “The report clearly recognizes the challenge that the transition poses to learned societies,” says Peter Knight, president of the Institute of Physics. “With more than two-thirds of the Institute’s charitable projects funded by the gift-aided profits from our publishing company, IOP Publishing, it’s crucial to us that the shift is managed carefully.”

And so to Oxford…

Edward Cowie

Edward Cowie, left, after yesterday’s world première of Particle Partita.


By Matin Durrani

“I loved it, I really loved it.”

So said one guy to me on the lawns of Balliol College, Oxford, at the drinks reception that followed yesterday’s world première of what was dubbed “a ground-breaking arts–science collaboration themed around the elementary particles”.

The event was a one-hour scientific “performance–lecture” presented by Oxford University particle physicist Brian Foster and the Brit Award-winning violinist Jack Liebeck, in which the pair linked the ideas of particle physics with music.

The concept was simple. Foster presented a bite-sized history of particle physics in eight parts, all the way from Democritus’s idea of atoms right up to the current hunt for the Higgs boson at CERN’s Large Hadron Collider. At the end of each part, Liebeck performed music specially written by the physicist, artist and composer Edward Cowie, with each of these eight short pieces reflecting – and being inspired by – the concepts just discussed by Foster.

Entitled Particle Partita, Cowie dubs the work “a sonic ‘history’ of particle physics” that follows the “ornate and beautiful actions and reactions” of particles’ charge, spin and symmetry. “It is a music of great complexity with many materials that re-emerge in altered but related forms from the opening to the close,” muses Cowie in the programme notes. Cowie also created special drawings for each piece that were displayed on a screen as Liebeck played in Oxford’s beautiful Holywell Music Room.

Drawing by Edward Cowie

The last of the eight pieces was a duet in which Liebeck was joined by Foster to perform “The Higgs boson – and beyond?”.

Foster and Liebeck are not, of course, new to the world of art–science collaborations, having been entertaining audiences for more than five years with their lectures Superstrings and Einstein’s Universe. Cowie, meanwhile, also collaborated with Bristol University’s Michael Berry in writing Rutherford’s Lights, a work for solo piano created as a homage to Ernest Rutherford.

Speaking in an interview with Physics World in 2010, Cowie wryly noted that many arts–science collaborations are “unholy marriages”. At turns sparse, dramatic and violent, the music of Particle Partita is certainly demanding of the listener, with Cowie himself admitting to me as we made our way in to yesterday’s first public performance that the music is “challenging”. One audience member, meanwhile, was overheard to say that the lecture went “right over my head”.

Particle Partita was commissioned with funds from the University of Oxford, the Alexander von Humboldt Foundation and the Institute of Physics, which publishes physicsworld.com. You can get a special, behind-the-scenes look at the making of the piece in this video we filmed last year.

Electrons feel the heat in new graphene photodetector

Researchers in the US have unveiled a new way of using graphene to detect light. The team’s graphene-based bolometer works in the infrared and although the first version of the device must be chilled to a very low temperature, newer models should work at room temperature, says the team. These devices could find applications in a wide range of areas, including security screening at airports, medical imaging and terahertz radio astronomy.

Previous schemes for using graphene – a honeycomb of carbon just one atom thick – to detect light have mostly focused on photoelectric or thermoelectric effects whereby light or temperature differences, respectively, are converted into electrical signals. By contrast, a bolometer is an instrument that absorbs light and turns it into heat. This heat affects the electrical resistance of the absorbing material, and it is this change that is measured.

Graphene could play an important role in the bolometers of the future because it can absorb light over a very wide range of wavelengths. These range from the ultraviolet to the infrared parts of the electromagnetic spectrum, and especially in the infrared. What is more, physicists know that electrons in graphene couple weakly to the lattice vibrations (phonons) in the material. This means that when these electrons absorb light, they heat up, but the atoms stay cool. “This allows the electrons to become much hotter than they otherwise would if they simply gave up their heat to the phonons,” explains Michael Fuhrer of the University of Maryland, who led the development of the new device.

Metal to semiconductor

In its normal state, however, graphene’s resistance is almost independent of temperature – which is not very useful for making a bolometer. Fuhrer and colleagues overcame this problem by using bilayer graphene in their device. They created two electrical gates: one above and the other below the bilayer. These gates are used to apply an electric field perpendicular to the layers. Doing this opens up a small band gap in the graphene, thus turning it from a metal to a semiconductor. The graphene is also connected to two gold electrodes, which are used to measure its resistance (see figure).

“The semiconducting bilayer graphene has a resistance that strongly depends on temperature and so makes for an excellent bolometer,” Fuhrer explains.

The current version of the bolometer only works at temperatures of about 6 K, so initially it could be used in applications where high sensitivity is required – such as in submillimetre-wave (terahertz) radio astronomy, for example. However, the researchers are busy developing a new version of the graphene bolometer that they believe will work at room temperature.

High-frequency readout

The team also plans to improve its low-temperature device. “The problem we have is that the bilayer graphene only absorbs a few per cent of incoming light and the semiconducting material is highly resistive, which makes high-frequency read-out difficult,” explains Fuhrer. “We are trying to enhance the absorption of light by taking advantage of plasmonic resonance in the graphene and are also looking at ways to lower the resistance of the device, such as by using superconducting electrodes.”

The researchers describe their work in Nature Nanotechnology.

Spintronic film senses magnetic fields

A new type of magnetic-field sensor that is tough, easy to make and works with high precision has been developed by physicists in Australia, Germany and the US. The device can detect fields of 1–340 mT and, although it is not the most sensitive sensor in this range, a big plus is that the device does not need to be cooled to ultracold temperatures nor be recalibrated.

The device is the brainchild of a team led by Christoph Boehme of the University of Utah, along with colleagues from the universities of Sydney and Regensburg. At its heart is a thin layer of organic semiconductor sandwiched between two metal contacts. When a voltage is applied across the contacts, electrons and holes are injected into the semiconductor. Being charged particles, the holes and electrons each induce a small local electric polarization of the semiconductor that follows the particles as they pass through the material.

This combination of particle and polarization is called a “polaron”; when a hole polaron and an electron polaron interact, they can decay to create an “exciton” – a bound state of an electron and a hole. It turns out that the resistance of the semiconductor is a function of the rate at which the hole and electron polarons interact, which in turn depends on the relative orientation of the electron and hole spins.

The clue to how the device operates lies in the fact that applying an external magnetic field creates an energy gap between spins pointing parallel and antiparallel to the field. So, if a radio-frequency (RF) signal at this precise energy is applied to the film, the spins are flipped up and down, causing a sharp change in the resistance of the semiconductor. As this resonant energy is a linear function of the magnetic-field strength, the field can therefore be measured by changing the RF energy until resonance is achieved.

Slow measurement

One drawback of the device associated with the need to scan radio frequencies is that it can take a few seconds to measure a magnetic field. Boehme told physicsworld.com that this should not, however, be a problem for applications where the user already has an approximate idea of the field strength – sensing Earth’s magnetic field, for example. But when speed is of the essence, the team has thought of two ways that the device could be improved.

One would be to apply RF pulses that incorporate the full range of frequencies, and the other would be to combine the technology with an organic magnetic-resistance sensor – which operates at high speeds but needs to be recalibrated regularly. This recalibration could be done using the new sensor, as it itself does not need to be recalibrated given that its output is related to an intrinsic property of the electron – the gyromagnetic ratio.

While the device operates in the 1–340 mT range, Boehme says that the upper limit could be extended by simply using a higher-energy RF signal. For extremely high fields, however, a terahertz signal would be needed and these are difficult to generate. As for extending the range below 1 mT, this could be done by applying a small offset field of about 1 mT , claims Boehme. The ultimate sensitivity of the device is in the low nanotesla range – a limit that is related to the random magnetic fields produced by the hydrogen nuclei in the organic semiconductor.

Best of both worlds

J T Janssen of the UK’s National Physical Laboratory says that the new device fits nicely between the much more-accurate superconducting interference device (SQUID) – which requires liquid helium to operate – and the less-accurate Hall sensor, which is robust and only costs a few pence to make. “This new organic sensor seems to have the best of both worlds: it’s reasonably sensitive, it’s accurate and it’s cheap,” says Janssen.

He adds that the device is particularly suited to “fit-and-forget” applications, in which it is not possible to service or calibrate the sensor once installed. Examples include sensors in nuclear power plants, wind turbines and satellites.

The sensor is described in Nature Communications.

Galactic mirage

NGC 3314 galaxies


Trickster galaxies. (Courtesy: NASA/ESA/ W Keel, University of Alabama)



By Tushna Commissariat

Over the years we have seen some fantastic images of colliding or interacting galaxies. Images of the closely entwined Antenna Galaxies, the Whirlpool Galaxy interacting with its satellite galaxy and the cheesily named Mice galaxies have caught our attention in the past.

So what exactly is special about the image above of two seemingly overlapping galaxies – called NGC 3314 A and B – captured by the Hubble Space Telescope They are a perfect example of “seeing is not always believing”, as the two galaxies are not interacting at all – in fact, they are tens of millions of light-years apart. The only reason that they look like part of a galactic pile-up is thanks to a celestial optical illusion – the two just happen to appear in that configuration from our point of view.

The main clue that led researchers to realize that there was no interplay between the two galaxies was their shapes. When galaxies are interacting, the enormous gravitational force of each galaxy distorts both galaxies out of their normal shapes, long before they even actually collide. These energetic distortions often affect the galaxies themselves, triggering new episodes of star formation that we observe as glowing nebulae.

In the case of NGC 3314, we do indeed see deformation in the foreground galaxy (NGC 3314 A), but this is a bit of a red herring. The distortion that is visible at the lower right of NGC 3314 A’s core, where one can clearly see streams of hot, blue-white stars extending out from the spiral arms, is not caused by any interaction with the background galaxy. Researchers think that the distortion is because of an encounter with another nearby galaxy to NGC 3314 A that can be seen in wide-field images.

Looking at the motion of both NGC 3314 galaxies, researchers say that the two are relatively undisturbed, and are moving independently of each other. This means that the galaxies are not, and indeed have never been, on any collision course.

Such a rare alignment of galaxies is proving useful to astronomers who want to study gravitational microlensing – another type of optical illusion that occurs when the gravitational field of a large astronomical body, such as star or a galaxy, causes small perturbations in the light coming from a more distant source, distorting it. Indeed, the observations of NGC 3314 that led to this image were carried out in order to investigate this phenomenon.

So while it does look very much as if the NGC 3314 galaxies are close-knit, they are nothing more than a chance alignment that gives us an interesting view.

What do you think would be the best thing about winning a Nobel prize?

By James Dacey

hands smll.jpg
This week the Nobel Foundation revealed that the prize money received by laureates is to be slashed by 20% because of ongoing financial difficulties. The announcement comes two and a half years after the foundation first announced that it might need to reduce the size of prizes, because the global financial crisis led to losses in its assets. As of this year, the prizes will be cut from SEK 10m to SEK 8m (£729,000), marking the first reduction in the value of the prize since 1949.

On first reading this, it seemed strange – and perhaps a little sad – to learn that a prize as prestigious as the Nobel could be as vulnerable to the economic climate as anything else. But then surely recipients don’t really care about the money because the real incentive for winning a prize is the freedom you would gain as a scientist and the recognition among peers? Hmm, well I’m not so sure. From my own experience, along with anecdotal evidence, I know that prize winners and would-be prize winners certainly don’t overlook the size of the prize money, even if this is not their main motivation. After all, most of these academics are not millionaires to begin with.

We want you to share your feelings on this issue by imagining that you were in a position to become a Nobel laureate, for this week’s Facebook poll question.

What do you think would be the best thing about winning a Nobel prize?

I wouldn’t want to win
Freedom to do the science that I want to do
The recognition that my field would receive
Securing a place in the history of science
The fame and all that comes with it

Let us know by visiting our Facebook page. As always, please feel free to explain your decision or suggest another benefit to winning the prize by posting a comment on the poll.

In last week’s poll we looked at the world of science fiction, by asking you to name your favourite author from the genre. It was a popular poll and it attracted some lively discussion, but the author who stole the crown in the end was the Russian-born American writer Isaac Asimov, attracting 56% of the vote. The other authors lined up as follows, Arthur C Clarke (17%), Ray Bradbury (8%), Stanislaw Lem (7%), Robert A Heinlein (6%) Larry Niven (3%), William Gibson (2%) and Kim Stanley Robinson (2%).

Thank you for all your contributions and we look forward to hearing from you in this week’s poll.

‘Seabed carpet’ could harness wave energy

A synthetic “seabed carpet” that mimics the wave-damping effect of a muddy seafloor could be used to extract energy from waves passing over it, according to an engineer in the US. As well as offering a new way to produce clean and cheap electricity, the carpet – which has not yet been built – could be used to protect coastal areas against strong waves and provide areas of safe haven for boats in stormy seas.

The ability of muddy seafloors to dampen ocean waves is well documented at various locations around the world. In the Gulf of Mexico, fishermen have learned to steer their boats into a local muddy spot known as the “mud hole” when a storm is brewing. Here, the wave–mud interaction is so strong that the storm waves are damped within a distance of a couple of wavelengths (100–200 m) and the boats there are completely safe.

Springs and generators

“If mud can seriously take so much energy out of ocean waves, then why don’t we use this idea to design a wave-energy convertor that’s very efficient?” asks the carpet’s inventor, Mohammad-Reza Alam of the University of California, Berkeley. He came up with the idea using a viscoelastic “carpet of wave-energy conversion” (CWEC) placed over a network of vertically oriented springs and generators on the coastal seafloor. The flexible carpet responds just like mud: as waves pass overhead, they induce dynamic ripples and undulations in its sprung surface, and these perturbations can be used to generate electricity.

Modelling the interaction of ocean waves with the proposed carpet, Alam was able to show that the system can easily absorb 50% of incident wave energy over short distances of about 10 m. For typical North Sea waves, the simulation suggested energy absorption rates of up to 6.5 kW m–2, which is more than double the maximum possible with wind turbines and at least 20 times greater than currently achieved by solar-power convertors.

Short waves are better

All oceanic motion is a combination of long and short waves. It has long been known that the short waves associated with choppy seas are dampened faster than far-reaching long waves (swells) for various reasons, but it was only recently that surprising field observations revealed that short waves are actually much better than long waves at imparting their energy to a muddy seafloor in shallow waters.

Alam developed a computer simulation that took into account hundreds of different waves and wave interactions. He found that when wave-damping conditions are strong – as is the case with a muddy seabed – a considerable amount of energy is converted from “surface mode” waves (where long waves dampen faster) to “bottom mode” waves (where short waves dampen faster and impart more energy to the seabed). “If damping is strong, the overall energy absorption from the ocean is even stronger,” he explains.

Bring on the storms

Alam believes that the CWEC presents a number of distinct advantages over existing wave-harvesting techniques. Chief among them is the fact that not only is the device resistant to storms, it actually performs better in them. Current approaches use moored floating devices or seabed-secured clam-like structures with vulnerable hinges. When waves become too energetic, these devices are designed to retreat into a protective idle mode, often by being pulled beneath the surface of the water.

The CWEC’s flat and fixed nature means that these issues are neatly sidestepped and it can continue harnessing power as the storm rolls by. Not only that, when non-linear elements of wave interaction – which increase during stormy seas – were introduced to the simulation, the efficiency of the device improved. The device also has a much broader bandwidth than most other wave-energy extractors, and can make use of any type of wave approaching from any direction.

The disadvantage of the CWEC is that its efficiency decreases with water depth, meaning that it is only suitable for use between the surf zone and depths of about 20 m.

Popular with mariners

A completely submerged carpet structure would likely be more popular with mariners and environmentalists than traditional devices, which can pose the threat of collision for ships and entanglement for marine mammals. The energy-draining effect could also be put to good use protecting vulnerable shorelines, sheltering harbours or protecting near-offshore platforms.

“It is an interesting idea but there are practical issues such as the cost of installation and maintenance, impact on [bottom-dwelling] marine life, and the impact of tides on the performance,” comments Dominic Reeve of Swansea University in the UK, who is part of the Wave Hub project – a large-scale testing facility for new wave-harvesting technologies that is based off the south-west coast of England. “If there is mobile sediment around, this carpet could well affect sediment transport – either to the detriment or advantage of itself or neighbouring areas.”

Alam agrees that sedimentation is certainly one of the concerns that would face engineers if the CWEC were to be built and trialled in the field. He suggests that perhaps the device would be best deployed along rockier coastlines.

The work is published in the Proceedings of the Royal Society A.

When physics was ‘made in the USA’

“The more important fundamental laws and facts of physical science have all been discovered, and these are now so firmly established that the possibility of their ever being supplanted in consequence of new discoveries is exceedingly remote.” So said Albert Michelson in 1899, before adding, for good measure, that future discoveries “must be looked for in the sixth place of decimals”.

Michelson had been saying this for some time and, in his defence, many others shared this “physics of decimal places” view with the man who would, in 1907, become the US’s first physics Nobel laureate. Yet James Clerk Maxwell, as early as 1871, had warned that such proclamations should not be taken seriously. He pointed out that the real reward for the “labour of careful measurement” was not greater accuracy but the “discovery of new fields of research” and “the development of new scientific ideas”. By the end of the century Maxwell was proved right as the discoveries of X-rays (1895), radioactivity (1896), the electron (1897) and the quantum (1900) transformed physics.

It is perhaps unfair to draw any firm conclusions about the relative state of American and European physics solely from the contrasting attitudes of Michelson and Maxwell, since Michelson himself mistakenly believed he was quoting a leading British physicist, Lord Kelvin. But it is certainly true that while early 20th-century European physicists produced a series of stunning breakthroughs and were busy trying to understand them, their colleagues in the US were still preoccupied with relatively settled topics such as electromagnetism, optics, acoustics and the electrical and thermal properties of materials.

In his slim but richly informative new book, A Short History of Physics in the American Century, the Hofstra University science historian David C Cassidy writes that “the task of history is not to celebrate achievements but to understand them as historical events, to explore and explain what happened, how it happened, and why it happened”. This is exactly what Cassidy does with some style as he traces the trajectory of US physics from its humble beginnings in 1900 to its pre-eminence by the 1950s – and, perhaps controversially, at least in his own country – “by the end of the century to a more modest place as an internationalized discipline within a global community of competitors”.

It comes as something of surprise to learn that in 1900 the US had more physicists than Germany. The trouble was that only three of them were theorists, compared with 16 at German institutions. American physicists did score some notable successes: during the first decade of the 20th century, physicists at US institutions were responsible for the first observations of the radiation pressure of light, the magnetic rotation of sodium vapour and measurements of the heat developed in a material caused by radioactivity. But the purely practical focus of their work also had a debilitating effect on the community, and the first to express concerns about it was Henry Rowland of Johns Hopkins University in Baltimore. After experiencing how physics was being done in Germany, Rowland championed a reorientation from applied to pure physics. In an 1883 address to the American Association for the Advancement of Science, the man who would go on to become the first president of the American Physical Society argued that “the proper course of one in my position is to consider what must be done to create a science of physics in this country, rather than to call tele-graphs, electric lights and such conveniences by the name of science”.

Rowland could not possibly have dreamed how dominant American physics (by which Cassidy means both the profession and the science) would become in the decades that followed. But change was coming: as the astronomer George Hale recognized, the First World War offered “the greatest chance we ever had to advance research in America”. By its end, scientific research in the US had been integrated into the nation’s economic and cultural affairs, although it remained second-rate throughout the 1920s, especially when compared with German contributions. Yet that too would soon change. Following the Nazi rise to power in January 1933, the next two years saw 278 physicists and 162 mathematicians fired from their posts for being Jewish or otherwise falling afoul of the Nazis. Hans Bethe, Albert Einstein and Eugene Wigner were just three of the 192 exiles who had found their way to the US by 1939. These emigrÄ scientists, many of whom were theorists, helped push the frontiers of American physics.

As victory in the Second World War approached, US President Franklin Roosevelt asked his director of the Office of Scientific Research and Development, Vannevar Bush (no relation to the later presidents Bush), to map the contours of the postwar relationship between science and the federal government. In 1945 Bush handed his report Science, the Endless Frontier to Roosevelt’s successor, Harry Truman. In it, Bush made the argument for permanent government funding of research to be undertaken “without thought of practical ends”.

The implementation of Bush’s recommendations ensured that by the 1950s and 1960s, aided by federal sponsorship and military funding, American physics led the world. Yet it was not to last. In the 1970s, with the US economy struggling under mounting debt, inflation and the impact of the Vietnam War, federal funding for research and development was drastically cut. As memories of the Cold War-era space race began to fade, so did the US commitment to scientific leadership, and the nation found itself struggling to maintain a competitive edge.

To some extent, corporations stepped in to fill the gap. Cassidy notes that from the early 1980s corporate sponsorship of research began to surpass state support, and by 2000 some 70% of all industrial R&D in the US was corporate-funded. Yet support for product-oriented development is not the same as support for the kind of “blue sky” research that would translate into commensurate breakthroughs in fundamental physics. Pure research was no longer insulated from the political, economic and social needs of society, and in retrospect, Congress’s decision to kill off the $11bn Superconducting Super Collider in 1993 in an attempt to reduce the budget deficit was only the most obvious sign of the decline.

For an account of the US academic physics community’s development from the late 19th century through the first two-thirds of the 20th, Daniel Kevles’ 1971 book The Physicists remains the standard against which other volumes are judged, and Cassidy is quick to admit this. However, he does a fine job of bringing the story of America’s physicists up to the threshold of the 21st century, and he also makes an interesting prediction about physics as a whole. To Cassidy, it seems unlikely that one nation will ever again dominate the field as the US once did, since the community of physicists is now truly international. Because of this, he writes, “it is doubtful that, a century from now, a similar history focused on physics in a single nation will be possible”.

At the moment, it appears that China is the nation most likely to prove Cassidy wrong. In the first decade of the 21st century, China more than doubled its research output, and its share of published physics papers rose from 8.2% in 2001 to 18.6% in 2010. Over the same period, America’s share fell by 3%. So will our descendants be reading A Short History of Physics in the Chinese Century? Perhaps. But as Michelson’s example shows, we should be wary about predicting future directions in physics research.

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