An employee shows visitors around Element Six’s new facility. Credit: Element Six
The Harwell Science and Innovation Campus added another jewel to its crown yesterday when the industrial-diamonds firm Element Six officially opened its £20m new R&D facility on the Oxfordshire site, which is already home to organizations such as the Rutherford Appleton Laboratory and the UK’s flagship synchrotron, the Diamond Light Source.
I’d heard about Element Six’s plans thanks to this article, which appeared in the careers section of June’s Physics World. The author, Stephanie Liggins, is a physicist who joined Element Six after completing her PhD at the University of Warwick, and towards the end of the article she mentioned that she would soon be moving to the company’s new Global Innovation Centre – which she described as “the world’s largest synthetic-diamond research and development facility”.
A new kind of camera that does not form a physical image has been developed by scientists in the US. Employing just a single sensor and an array of apertures rather than a lens, the device can acquire the image of a scene using fewer measurements than conventional cameras. According to its inventors, it would be particularly good for surveillance operations and could also be adapted for non-visible imaging at wavelengths such as infrared, millimetre-wave and terahertz.
Conventional cameras use a lens to project an image onto photographic film or an array of charge-coupled devices. What Paul Wilford and colleagues of Alcatel-Lucent’s Bell Labs in New Jersey have instead done is to use a single point-like sensor to record the intensity of light that has passed through an array of tiny apertures placed between the object and the sensor. The researchers essentially create an image in time instead of space and do so using just a fraction of the measurements needed in normal digital cameras.
One aperture at a time
Each of the apertures in the array can be independently opened and closed using a computer. The simplest way to record an image is to open one aperture at a time, measuring the intensity of the light arriving at the sensor that has bounced off the object and passed through just that aperture. The number of required measurements is therefore the number of apertures, with the process equivalent to building up an image from a pinhole camera one pixel at a time.
Instead of using this simple method, the team uses an established signal-processing technique known as compressive sensing to reduce the amount of data needed to reconstruct an image. Wilford and colleagues do this by generating pseudo-random patterns of open and closed apertures within the array. Rather than measuring the intensity of light passing through one aperture at a time, the combined intensity from all of the apertures (open and closed) is measured. It then generates another pseudo-random pattern and measures the light transmitted by that, and so on.
“The pseudo-random patterns of the apertures make it possible to capture the information from the scene with a reduced number of measurements,” explains Wilford.
LCD apertures
The team built its aperture array from a monochrome liquid-crystal display (LCD) comprising some 65,000 squares that can be made either transparent or opaque. The sensor is a single pixel from a photovoltaic sensor that records the intensity of red, blue and green light falling on it. The research group enclosed the array and sensor inside a light-tight box about the size of a small microwave oven and used a computer to generate the aperture patterns and synchronize this pattern generation with the recording of the intensity measurements. These measurements were then converted into images in a separate step.
Result: This image of a football was produced using just an eighth of the measurements needed by a conventional camera. (Courtesy: Gang Huang, Hong Jiang, Kim Matthews and Paul Wilford/Bell Labs)
The researchers imaged a football, a pile of books and a toy sleeping cat, and found that they could generate reasonable images of these objects using just a quarter (or in the case of the football an eighth) of the measurements that would be needed using a conventional camera. They also imaged the books using two sensors in different positions at the same time, showing how multiple sensors can be used either to reduce the time needed to capture an image or to improve its resolution.
According to Wilford, the device has a number of advantages over conventional cameras. The absence of a lens, he says, potentially makes it cheaper, lighter and free of distortions, with the image quality in theory only limited by the resolution of the aperture array. He adds that the device could be used for low-power imaging, since only a fraction of the data is collected at source and no processing is required to compress the image. The camera would be particularly well suited to surveillance, where the aim is to record changes in a scene and not to make detailed images of it. Wilford adds that it might also be used for imaging at different wavelengths where sensors are expensive.
Technical hurdles
However, the team acknowledges that it must overcome a number of technical hurdles before commercializing its device. The main one is speed. Limited by the working frequency of the LCD display and the sensor’s response time, one picture takes between several minutes and an hour to acquire. Boosting the frequency will mean making the apertures much smaller if energy consumption is to be kept under control. One option, according to Wilford, is to use microelectromechanical systems (MEMs) – moving devices built from components measuring as little as microns across.
Tiny, fast-moving apertures introduce a new problem – how to collect enough light in each measurement to create an image. A rival team at Rice University in Texas has made a similar device but has used lenses both to focus the light from an object onto an aperture array and then to direct the outgoing light on to a single-pixel sensor. Wilford admits that increasing the signal-to-noise ratio of his group’s sensor to the point where it can cope with the aperture speeds needed to produce videos will be “a challenge”, but underlines his group’s desire to “get away from this idea of creating a physical image”. “We face a number of practical issues,” he says, “but this is not by any means outside the realm of today’s technology.”
A new documentary of Stephen Hawking’s life is due in cinemas later this summer, with the esteemed physicist himself narrating the film. Hawking, as the documentary is simply dubbed, takes a personal look at the life of the celebrated scientist – his early days as a student in Oxford and his ongoing battle with motor neurone disease – as well as documenting his academic achievements.
Smiles all around in Paris. From left to right are ILL director-general Andrew Harrison, Hermione Gough of the British Embassy, the French minister for higher education Geneviève Fioraso and Peter Reuss of the German Embassy. (Courtesy: ILL)
By Hamish Johnston
Despite the tough economic conditions in much of Europe, scientists who use one of the continent’s leading scientific facilities have something to smile about. The UK, France and Germany have agreed to continue funding the Institut Laue-Langevin (ILL) neutron facility for at least another decade.
A new type of optical fibre that can carry “twisted” light over long distances has been developed by researchers in the US, Israel and Denmark. Their “vortex fibre” and associated encoding and decoding technologies allow data to be transmitted using the orbital angular momentum (OAM) states of light. In principle, the system could be used to increase the rate at which information can be sent along an optical fibre – and could ultimately boost the data-traffic capacity of the Internet.
As more information is sent across the Internet, researchers are looking for new ways of boosting the data capacity of the optical fibres that carry digital communications. While there are several new schemes under development, they all have drawbacks, such as the need for intensive signal processing or complicated multicore fibres.
Recently, scientists have shown that information can be encoded into the OAM of light. Light with OAM has a wavefront that rotates around the propagation axis, creating a spiral or vortex. By contrast, an ordinary light beam has a wavefront with an orientation that remains fixed with respect to its direction of propagation.
Coupling problems
In principle, OAM could be combined with conventional multiplexing techniques to boost the rate at which data can be transmitted along optical fibres. A major problem, however, is that even the slightest bend, twist or temperature variation in a fibre can cause light in one OAM transmission mode to jump into other modes. This coupling of modes leads to the rapid loss of information and it was only possible to send OAM-encoded data less than a metre along conventional fibres.
Cross-section of the vortex fibre: Microscope image of a cross-section of the vortex fibre showing the circle and concentric ring with greater indices of refraction than the rest of the fibre. (Courtesy: Nenad Bozinovic et al. Science340 1545)
A new system that gets around this problem has been created by Siddharth Ramachandran and colleagues at Boston University, Alan Willner’s group at the University of Southern California (USC), researchers at Tel Aviv University and the fibre-maker OFS-Fitel, Denmark.
According to Ramachandran, who led the development of the fibre, the new system is designed so that the phase velocities of the OAM modes are different. This minimizes the probability of coupling between modes as the signals propagate along the fibre.
Circle and ring
At the centre of their new fibre is a region about 8 μm in diameter that comprises an inner circle and a concentric ring (see figure “Cross-section of the vortex fibre”). Both of these regions have indices of refraction that are greater than the rest of the fibre. This fibre is designed to carry four distinct modes – two zero-OAM modes that propagate in the inner circular core and two OAM modes that propagate in the outer ring. As well as minimizing the coupling of light between the zero-OAM and OAM modes, the design also reduces coupling between the OAM modes and two other “parasitic” modes that could occur in a fibre.
About 1.1 km of the fibre was manufactured by OFS-Fitel. “We were intent on showing this to work only with fibres that could be produced in a real production environment and all the fabrication steps we used were identical to those used in commercial producing optical fibres,” explains Ramachandran.
Development of the system that encodes and decodes the OAM pulses was led by Willner at USC. Dubbed OAM mode-division multiplexing (OAM-MDM), the system encoded data into four separate channels. These are defined in terms of the OAM (0 or 1) and circular polarization (–1 or 1) of the light. Using just these four modes, the team was able to transmit data over a 1.1 km fibre at a rate of 400 Gbit/s.
Eight Blu-rays per second
The system was also able to reproduce each quartet of OAM modes at 10 different wavelengths of light – a technique called wavelength-division multiplexing (WDM). This boosted the transmission rate to 1.6 Tbit/s – the equivalent of transmitting eight Blu-ray discs every second. While such data rates are routinely achieved by commercial WDM systems, this is the first time that OAM-based transmission has been achieved over distances greater than a metre.
Ramachandran believes that the transmission could be further boosted by minimizing losses in the system. “The one good thing about having started with fibre fabricated on a real production line is that it gives us hope that, where/when OAM supporting fibres are needed, our approach would have already addressed the manufacturability issue,” he adds.
John Pendry has won the 2013 Isaac Newton Medal of the Institute of Physics. (Courtesy: Imperial College London)
The British theoretical physicist who helped build the first working “invisibility cloak” has won the 2013 Isaac Newton Medal of the Institute of Physics, which publishes Physics World. John Pendry of Imperial College, London, receives the international award for “his seminal contributions to surface science, disordered systems and photonics”. The Newton medal – the Institute’s most prestigious prize – has been awarded annually since 2008.
The medal is given for “outstanding contributions to physics” and includes a £1000 prize. This year’s award will be presented at a ceremony in London on 15 November and Pendry will also give the Institute’s Newton Lecture in October. Previous winners of the medal include Martin Rees, Leo Kadanoff, Edward Witten, Alan Guth and Anton Zeilinger.
Perfectly elegant
In a career spanning nearly 50 years, Pendry has worked on the physics of surfaces, low-energy diffraction and X-ray spectroscopy. However, he is probably best known for his more recent work on “metamaterials” and also on “transformation optics” – a concept that he developed. This research has led to the experimental realization of invisibility cloaks, perfect lenses and other remarkable electromagnetic devices.
Metamaterials are engineered structures that respond to electromagnetic waves in unusual ways, such as having a refractive index that varies throughout and even – in some cases – taking on a negative value. In a landmark paper published in Physical Review Letters in 2000, Pendry described how a metamaterial could be created with a negative index of refraction for microwave radiation. Such a structure was built the following year by David Smith and colleagues at the University of California, San Diego. In 2006 Pendry teamed up with Smith (now at Duke University) and colleagues to use negative-index metamaterials to create the first invisibility cloak.
While the mathematics describing how electromagnetic radiation interacts with metamaterials can be complicated, Pendry realized that it could be described elegantly by borrowing ideas from Einstein’s general theory of relativity, which is the basis of transformation optics.
“In his illustrious career, John has revolutionized the way physicists think of materials and, in particular, the way materials react to light,” says Peter Knight, president of the Institute. “His theories have inspired experimentalists around the world to design metamaterial devices including, of course, the highly anticipated invisibility cloak.”
You can also watch John Pendry’s colleague at Imperial College, Martin McCall, explain how invisibility cloaks work in the video “Can we make objects invisible?“.
Physics World July 2013 special issue on the physics of cancer.
By Matin Durrani
Medical physicists have made – and continue to make – many valuable contributions to the treatment, diagnosis and imaging of cancer using X-rays, magnetic fields, protons and other subatomic particles. But some physicists are trying to tackle cancer through a very different approach. Rather than seeing cancer purely in terms of genetic mutations, these researchers are instead examining the physical parameters that control how cancer cells grow, evolve and spread around the body.
Find out more by downloading your free PDF copy of the July 2013 special issue of Physics World on the “physics of cancer”.
Science for art’s sake: David Meyer as an elderly Sir Isaac in the play Let Newton Be!, which has now been published along with essays about Newton. (Courtesy: Menagerie Theatre Company)
Let Newton be!
Isaac Newton was not a fan of the theatrical arts. On the one occasion when he is known to have attended an opera, he ran away during the third act. So it seems fair to surmise that the father of gravitational theory would have absolutely hated Craig Baxter’s play about his life, Let Newton Be! That, however, is no reason for the rest of us to avoid this excellent work. First performed in 2009 at Newton’s own Trinity College, Cambridge, the play toured a handful of institutions in the UK and US in 2011; however, as a physicsworld.com reviewer argued at the time (“Newton’s three body problem”, 30 March 2011), it deserved a much wider audience. Fortunately, someone in the publishing world agreed, and the play is now available in book form as The Isaac Newton Guidebook. In addition to the text of Let Newton Be!, the guidebook also contains a series of scholarly essays on various aspects of Newton’s life, introductions by both Baxter and Stephen Hawking and – best of all – a DVD of a performance by the splendid Menagerie Theatre Company. Probably the most useful of the essays is the one on Newton’s feud with Leibniz. The nature of this dispute was so complex, wide-ranging and important that Newton novices should probably read the essay about it before watching the play. Other than that, though, this is not a work that requires much introduction. Just sit back and enjoy the spectacle as the three different actors who play Newton take you through his life, his works, and his famously difficult personality.
2012 Faraday Publishing £25.00/$40.00hb 176pp
Getting spammed
“Mail is easily deleted and so ‘junk’ mail is not really a serious problem.” As an example of faulty prognostication, this statement – made in 1978 on a mailing list of ARPANET, the progenitor of today’s Internet – surely ranks right up there with Lord Kelvin’s supposed declaration that, by 1900, nothing new remained to be discovered in physics. The story of how junk e-mail, or “spam”, evolved from a minor nuisance into a serious problem is thoughtfully and engrossingly told in Spam: a Shadow History of the Internet. Written by Finn Brunton, a historian of technology at the University of Michigan, US, the book is initially rather hardgoing, with clunky phrases such as “foundational ambiguities”, “root paradigm” and “co-constitutive feedback loop” marring the introduction. However, once this little display of academic impenetrability is finished, Brunton the storyteller takes over. The rest of the book is pacey and packed full of interesting titbits, from the tale of the first commercial spam message (an advert for DEC computers that appeared on ARPANET on 1 May 1978), to an inside look at the professional spammers who plagued the loosely organized Usenet in the mid-1990s, and finally a sobering assessment of new forms of spam that seek to game search-engine algorithms. Like all good historians, Brunton is an interpreter as well as a narrator, skilled at placing facts in context. That ARPANET post about junk mail, for example, made sense at the time because its audience was a community of computer scientists, engineers, physicists and other defence experts who were used to collaborating and often knew each other personally. As Brunton puts it, the proto-Internet “was not the electronic frontier but a fairly small town, populated almost exclusively with very smart townspeople”. Once that population expanded, old strategies for keeping noxious behaviour under control – including ad hoc flame wars and revoking offenders’ access privileges – ceased to function. New ones had to be developed to replace them, and as Brunton explains, this is still very much a work in progress.
2013 MIT Press £19.95/$27.95hb 304pp
Alea iacta est
What does it mean for an event to be truly random? For science writer Brian Clegg, the answer depends on whether you are talking about classical randomness or chaotic randomness. As he explains near the beginning of his book Dice World: Science and Life in a Random Universe, classical randomness applies to things like roulette wheels and gambling dice: the outcome of a dice throw is uncertain, but it can be predicted using the standard tools of probability theory. Chaotic randomness, on the other hand, is the stuff of earthquake clusters, flapping butterfly wings and – in Clegg’s view, at least – the mysterious alchemy that transforms a handful of books into bestsellers. These things, he explains, are not actually random at all in the classical sense, because they cannot be controlled and are not easily predicted. Once this distinction is established, the rest of the book takes the reader on a tour of various forms of randomness and the methods scientists and mathematicians have developed to describe them. In addition to relatively well-known pioneers such as Blaise Pascal and various members of the talented Bernoulli family, Clegg also highlights the work of some lesser-known contributors to the field, including the Italian scholar and gambler Girolamo Cardano (see May 2009 pp36–40) and John Graunt, a button-seller with a sideline in statistics who became a member of the Royal Society. A light, quick read overall, the book does get into some weighty material later on, when quantum randomness and Bayesian statistics enter the picture.
Magnetic anomalies created by tsunamis could be detected by satellites. That’s the claim of researchers in China, who have created a model that simulates the effect of huge ocean waves on the Earth’s magnetic field. The team believes that its work could lead to an early-warning system that can detect the deadly waves in real time.
Tsunamis are huge ocean waves often associated with earthquakes. While they can be tens of metres high when they reach land – often with devastating effects – they tend to have amplitudes of a metre or so in the open ocean. As a result it can be difficult to spot a tsunami against a background of normal waves.
While a tsunami in the open ocean might not be tall it is extremely long and fast moving and therefore involves the rapid displacement of large amounts of water. When a body of salt water moves through the Earth’s magnetic field its conductive nature induces a small anomaly in the field, which can be with a magnetic sensor mounted on a low-Earth-orbit satellite or high-altitude balloon.
Real and model tsunamis
Now, Benlong Wang and colleagues at Shanghai Jiao Tong University have developed a way to predict the local changes in the Earth’s magnetic field caused by a variety of model tsunamis. The basic models can then be combined to simulate the magnetic behaviour of a real-life tsunami. To test these models, the team compared its predictions with data recorded during the 2004 Sumatra and 2010 Chile tsunamis. The team was able to spot magnetic anomalies associated with the events and then estimate the wavelength and height of the tsunami waves.
In principle, a calculation of the tsunami wave profile from a magnetic signal can be done almost instantaneously, Wang told physicsworld.com. If applied in practice this could result in a marked improvement in tsunami early-warning systems. Today’s seismic detection methods, for example, can often take about six minutes to process. A further limitation of seismic prediction and alternative methods based on tidal gauges is that they cannot do continuous tracking of the wave as it moves in the open ocean – whereas magnetic monitoring could be capable of achieving this.
While the technology to detect these magnetic anomalies exists, a suitable infrastructure will need to be developed to provide a comprehensive early-warning network. There are two possible approaches to this, the team explains: using unmanned near-space airships or low-Earth-orbit satellites – both of which are close enough to the ocean to detect the magnetic signal of the wave.
Detection could be problematic
In practice, however, detecting the tsunamis may be more problematic than the researchers claim. “The tsunami magnetic signals are typically about 1–2 nT – compare this with about 40,000 nT of ambient geomagnetic fields,” says Manoj Nair, a geomagnetism expert at the University of Colorado, who was not involved in this study. Nair suggests that, while the researchers may have succeeded in detecting the tsunami signals retrospectively on the magnetic records, real-time detection comes with new challenges: “This is because the time variations in the geomagnetic field from other sources can overwhelm the weak tsunami magnetic signals. I am more sceptical on the use of satellites since [they see] a mix of time and space signals, further complicating the separation of tsunami signals from other sources.”
Nevertheless, Wang and colleagues will continue to test their model against other historical tsunami data. “The next step of our work will focus on the realistic tsunami wave history at Easter Island,” Wang explains. Located in the South Pacific, the island was struck by the 2010 Chile tsunami. The team will use magnetic data gathered from this region in conjunction with global tsunami propagation models to further its understanding of the connection between magnetic anomalies and the sea-surface variations.
The group also plans to look at the magnetic effects of internal waves and tides – movements of water that occur beneath the surface of the ocean and are important in heat and material exchanges between different ocean layers. “Using magnetic signals,” Wang adds, “we expect that these internal flows can be observed conveniently.”
Artist’s concept of NASA’s Voyager spacecraft. (Courtesy: NASA/JPL-Caltech)
“It is the consensus of the Voyager science team that Voyager 1 has not yet left the solar system or reached interstellar space.”
That is what Voyager scientist Edward Stone had to say on the matter back in March following reports that NASA’s most intrepid explorer had finally passed beyond the edge of our solar system. Today, three new papers published in Science back up this statement, asserting that the Voyager 1 had instead entered a distinct section at the edge of the solar system.
