Was Bacon a hero or villain of science? (Courtesy: Sheila Terry/Science Photo Library)
Francis Bacon – the Elizabethan philosopher, not the 20th-century painter – seems to inflame people. Hillary Clinton has spent two decades having her every sneeze scrutinized for evidence of misconduct, but Bacon has received that treatment for the better part of four centuries.
The son of an official in Queen Elizabeth’s court, Bacon (1561–1626) grew up around the royal household. He became a barrister, member of parliament and attorney general. Bacon befriended the Earl of Essex, who advised the queen, but then helped level charges of treason against Essex, who was executed in 1601. Bacon became lord chancellor under Elizabeth’s successor, James I, but fell from power after being accused of bribery in 1621. The practice of bribery appears to have been widespread and the charges against Bacon seem to have stemmed from anti-royalist sentiment in parliament. Sensing he now lacked James’s support, Bacon prepared a defence, then dropped it and admitted the charges.
Bacon sought political influence to advance his far-sighted dream of what science on a grand scale could look like – and how it could remake England. He presented his vision in Instauratio Magna (“Great Instauration”), one of the most ambitious works ever written. Published in 1620, it outlined “a total reconstruction of sciences, arts and all human knowledge, raised upon the proper foundations” to restore the proper relation of humanity and nature. His contemporaries almost uniformly praised Bacon for his work. The poet Abraham Cowley likened him to Moses, who led his people out of Egypt, while Samuel Taylor Coleridge called the Novum Organum (part two of Instauratio Magna) “one of the three great works since the introduction of Christianity”.
Many later writers, however, saw Bacon as initiating the evils of modern civilization. He’s been called “the most wicked man in recorded history” and a “creeping snake” with “viper eyes”. Many invoke Alexander Pope’s quotable couplet: “think how Bacon shin’d/The wisest, brightest, meanest of mankind”. Pope’s lines were cited by others, including the early 19th-century British politician Lord Campbell, who claimed that Bacon was “THE MEANEST OF MANKIND!!!” using all caps and triple exclamation marks for emphasis. In 1978 Anthony Burgess blamed terrorism on “a Baconian faith”, claiming (falsely) that Bacon held that creating a new future requires destruction of the past, while in 1985, Time magazine lumped him alongside US presidents Garfield and Nixon as a famous corrupt politician.
Character assassination
A casual reader might therefore assume that Bacon was materialistic, utilitarian, power-hungry and heartless. But in her 600-page 1996 book Francis Bacon: the History of a Character Assassination, Nieves Mathews concludes that nearly all the charges against him are based on mistaken – or at least uncharitable – apprehensions. Even the word “meanest” in Pope’s couplet may well signify “unassuming” rather than “villainous”.
Similar misreadings characterize most other accusations. The evidence against Bacon, one could say, has been cooked.
Mathews’ book deals mainly with character assassinations, but there have also been what we might call philosophical assassinations, which regard Bacon’s vision of science as not only misguided but immoral and inhuman. In the 1920s, for example, German philosophers and sociologists from what’s known as “the Frankfurt school” saw Bacon as initiating a misplaced optimism in science and a narrow, overly rationalist approach to social problems. One early member, Max Horkheimer, even compared Bacon to a criminologist whose idea of obtaining trustworthy knowledge is the sort of thing you can only do in a police laboratory.
More recently, “ecofeminist” philosophers have charged Bacon with promoting a style of science based on patriarchal gender roles. Sandra Harding from the University of California, Los Angeles, for example, saw him as advocating the “marital rape” of nature – that is, “the husband as scientist forcing nature to his wishes”. Bacon, she wrote, “appealed to rape metaphors to persuade his audience that experimental method is a good thing”. Meanwhile, Carolyn Merchant from the University of California, Berkeley, charged Bacon with “treat[ing] nature as a female to be tortured through mechanical investigations”. She cites Bacon’s discussion of the fable of Proteus – which Bacon interprets as a parable about scientific experimentation – in which Bacon notes that Proteus must be “vexed” before he shows himself as what he is.
Recently, other scholars have argued that, when cited correctly and read in context, such passages are literary embellishments rather than substantive descriptions of Bacon’s vision. Peter Pesic of St John’s College in Santa Fe, for instance, shows that Bacon was using the word “vex” to mean something more like “perturb” than “torture”; Bacon, Pesic argues, was advising us to see how a phenomenon acts in its myriad ways before we try to say what it is.
The critical point
The assassination attempts on Bacon reveal the danger of not going back to the original sources to understand them in context. Bacon, a lawyer, was a perceptive and versatile speaker who knew the value of, and was skilled at, speaking in different ways to different audiences. This makes it easy to support contemporary misinterpretations of Baconian science – that it’s all about patriarchy, or the domination and control of nature, for instance – by picking and choosing remarks out of context.
Bacon noted that the human mind is vulnerable to certain flaws that distract us from seeing nature as it is. He called them idols, and described four: idols of the cave, the tribe, the marketplace and the theatre (June 2013). We might describe a fifth, the idol of the inkblot, referring to the human tendency to project our own feelings onto someone or something else. Analysing examples of this fallacy reveals many of the assumptions and prejudices about science that we have inherited. By studying Bacon, we can therefore learn much about our age’s attitudes to science, as well as about his.
Physicists working at the Gran Sasso National Laboratory in central Italy, located 1400 m under the mountain of the same name, are soon to start taking data from two new experiments. Each facility will target a different kind of missing matter: one will search for dark matter while the other will try and detect absent neutrinos to prove that neutrinos are their own antiparticle.
Dark flash
The hunt for dark matter – the mysterious substance believed to make up about 80% of all matter in the universe but not yet detected directly – will be carried out using XENON1T. This experiment, which was inaugurated at an event at Gran Sasso today, consists of 3.5 tonnes of liquid xenon. It is designed to measure very faint flashes of light that are given off whenever particles from the dark matter halo of the Milky Way collide with the xenon nuclei. The xenon will be stored at a temperature of about –100 °C in a cryostat and surrounded by a tank containing some 700 tonnes of purified water to minimize background radioactivity.
Run by an international collaboration of 120 students and scientists from 22 institutions, XENON1T is expected to be about 100 times more sensitive than its 160 kg predecessor experiment and around 40 times better than the world’s current leading dark-matter detector – the 370 kg Large Underground Xenon experiment in South Dakota, US. Due to start taking data by the end of March next year, XENON1T will either detect dark matter or place severe constraints on the properties of theoretically-favoured weakly interacting massive particles (WIMPs), says collaboration spokesperson Elena Aprile of Columbia University in New York.
Dark heart
The other new experiment at Gran Sasso is the Cryogenic Underground Observatory for Rare Events (CUORE), which will look for an extremely rare nuclear process known as “neutrinoless double beta decay“. That decay, if it exists, would involve two neutrons in certain nuclei decaying simultaneously into two protons while emitting two electrons but no antineutrinos (unlike normal beta decay), implying that the neutrino is its own antiparticle. Due to turn on early next year, CUORE will measure the energy spectrum of electrons emitted by 741 kg of tellurium dioxide surrounded by radioactively inert lead blocks recovered from a Roman ship that sank 2000 years ago.
Meanwhile, towards the end of 2016 another group of scientists at Gran Sasso should take delivery of about a kilogram of cerium oxide powder, which they will place several metres below the Borexino neutrino detector. The Short Distance Neutrino Oscillations with BoreXino (SOX) experiment will look for a sinusoidal-like variation in the number of interactions generated within the detector by neutrinos from the radioactive cerium. SOX leader Marco Pallavicini of the University of Genoa says that such a variation would be a sure sign of “sterile” neutrinos – hypothetical particles outside the Standard Model of particle physics that would “oscillate” into ordinary neutrinos but would not interact with any other kind of matter.
In the video below, Luke Davies of the University of Bristol explains why physicists believe that the universe is full of dark matter
People have long been fascinated by extreme environments and those who explore them. Back in 1969, some 800 million of us tuned in to watch Neil Armstrong set foot on the Moon, while earlier generations thrilled to hear news of Roald Amundsen’s 1911 journey to the South Pole or Edmund Hillary and Tenzing Norgay’s 1953 conquest of Mount Everest. Yet despite the daring of human explorers, it is remarkable that wherever we have ventured on Earth, we have always found that other organisms got there first.
From the inky ocean depths to the driest deserts and the coldest reaches of the polar regions, all of the most inhospitable places on the planet have been colonized. In fact, the greatest explorers of our time may not be humans at all, but the extreme-loving organisms known as “extremophiles” that can survive and thrive in physical and chemical environments that would kill most other forms of life.
The study of extremophiles has a remarkably short history. As recently as 1965, scientific dogma held that no organism could live at temperatures above 55 °C. In that year, however, biologist Thomas Brock began exploring the waters of superheated geothermal pools in Yellowstone National Park, US. Brock observed bacteria growing in springs with temperatures up to 88 °C, and he and his colleagues eventually isolated a previously unknown genus of bacteria, Sulfolobus, that thrives in temperatures of between 75 and 80 °C.
The study of extremophiles really took off after 1977, when researchers using the submersible vessel Alvin discovered an oasis of life more than 2000 m below the surface of the Pacific Ocean off the Galapagos Islands. There is no sunlight at such depths, so instead, the organisms that call this environment home produce organic material via chemosynthesis. In this, they are helped by underwater geysers known as “black smokers”, which spew out superheated water laced with minerals such as sulphide (which gives them their bleak colour) at temperatures that can exceed 400 °C. This water is also highly acidic, with a pH as low as 2.8 – similar to vinegar, which has a pH of 2.2.
Today, the list of known extremophiles is impressively long. As well as the hyperthermophiles and acidophiles mentioned above, there are alkaliphiles, which survive and thrive in habitats with a pH above 9; halophiles, which flourish in highly salty waters such as the Dead Sea; and psychrophiles – cold-loving organisms found in the deep ocean at temperatures of 1–3 °C and at much lower temperatures below (and within) polar ice caps. There are even some organisms that thrive in multiple extreme conditions, such as the bacterium Deinococcus radiodurans. This beautiful example of a “polyextremophile” can survive cold, dehydration, vacuum and acid. Remarkably, it can also withstand a 5000 Gy dose of ionizing radiation with no loss of viability – a staggering amount compared with the 5 Gy dose that would kill a human.
With each discovery, new questions have emerged about the mechanisms that allow these organisms to survive. In our own bodies, extremes of temperature, both high and low, and extremes of pH will destroy DNA and other fundamental biological molecules in our cells. So how do extremophiles manage to tolerate such conditions? The answer is not yet clear, but research at the interface between the physical sciences and biology is providing insights into the complex processes of life in extreme environments. The physics aspect is important because at the cellular and molecular level, biological processes are noisy and stochastic, involving vast numbers of random motions and interactions. Many fields in physics are vital for exploring these complex processes, with knowledge from thermodynamics, statistical mechanics, soft-matter physics and more being brought to bear. These fields provide powerful methods to probe the processes of life in extreme environments in a quantitative and predictive way.
Physics has also given us a different and powerful approach to studying life in extreme environments. The physical properties of extremophiles are often discussed in terms of their equilibrium properties, such as their thermodynamic stability and static structures. We can also gain valuable insights into these systems by examining their kinetic stability, as well as the fundamental forces that govern their functions. We can develop a theoretical description of their behaviour, for example by using scaling laws borrowed from polymer physics. Finally, the development of new instrumentation adapted to extreme pressure, temperature and/or chemical environments has also been integral to advancing our knowledge of extremophile life – particularly since many of these organisms cannot survive in “normal” laboratory conditions.
Keeping it together
In the eyes of biological physicists, globular proteins are colloids, DNA is a stiff polymer and lipids forming cell membranes are surfactants. Extremophiles (and indeed other organisms) are almost entirely made up of “living soft matter”. Physics-based approaches make it possible to measure the forces and fluctuations that shape the dynamics and functionalities of these components, including single biological molecules as well as the larger molecular machinery of the cell.
Proteins, in particular, are fascinating for scientists investigating the extraordinary toughness of extremophile life. These chains of polymers are made up of monomeric units called amino acids, and they provide the workforce that keeps cells functioning – they are, in effect, “bionanomachines”. Proteins fold into a characteristic 3D shape that governs their function, stiffness, elasticity and adhesive properties, all of which play important roles in their various jobs, which include moving other molecules across a cell membrane and providing mechanical robustness in muscle function.
Despite being so useful, though, proteins are rather fragile. To perform their numerous functions, their structures need to be dynamic and flexible. Protein structures are stabilized by a large number of weak, non-covalent interactions, such as hydrogen bonds, ionic interactions, van der Waals forces and hydrophobic interactions. Given that the forces that maintain protein structure are weak, at room temperature the resulting dynamic structure of the protein can be described as malleable, or “mechanically soft” – in other words, they lose their structure when subjected to moderate perturbations. At higher temperatures, molecular vibrations from heat can literally shake a protein apart, unravelling its polymer chain or preventing new proteins from folding correctly once made. Without these protein workhorses, the normal biological machinery of the cell will not operate. How, then, do the proteins in heat-loving extremophiles manage to remain intact?
Applications of extremophiles
Chain reaction A molecular model of Taq polymerase (blue) replicating DNA. Taq is derived from the heat-resistant bacterium Thermus aquaticus. (Courtesy: Dr Tim Evans/Science Photo Library)
Much of the research on extremophiles has focused on answering fundamental questions about how these organisms survive. But there is also a growing industry that seeks to exploit enzymes isolated from organisms that can tolerate extremes of heat, cold, acid, pressure and more. A classic example concerns the heat-loving bacteria species Thermus aquaticus, which was discovered by Thomas Brock and Hudson Freeze in 1969. This bacterium is the source of a heat-resistant enzyme called Taq polymerase, whose job is to assemble a new DNA strand from individual nucleotides.
Taq is now a key component of a technique called polymerase chain reaction (PCR), which can generate thousands (sometimes even millions) of copies of a particular DNA sequence in a few hours using simple equipment. PCR has revolutionized biochemical and genetic research (its creator, Kary Mullis, shared the 1993 Nobel Prize for Chemistry) and it relies completely on the high-temperature adapted capabilities of the Taq enzyme, which must survive cycles of repeated heating and cooling of the DNA between about 68 and 96 °C.
Other applications of extremophiles include using extremophilic enzymes to recover gold, copper and other valuable metals from solid industrial wastes or to degrade toxic compounds. Such enzymes are also being used in agriculture (to modify crops to protect them from cold weather conditions) and to lower costs in the baking industry by making enzymatic reactions more efficient at lower temperatures. Understanding the structure and stability of extremophilic proteins is central to all of these industrial developments.
A myriad of adaptations
One conceptually attractive possibility is that the high thermal stability of proteins in thermophiles might be correlated with the high mechanical rigidity of the protein matrix. But fundamentally all proteins are made from the same collection of amino-acid building blocks. So how can two proteins display such differences in stability and therefore survive different environmental extremes? To answer this question, researchers have drawn on a treasure trove of data known as the protein database (PDB), which contains 3D structural data on proteins.
The first protein structure was solved in the 1950s by John Kendrew and Max Perutz (earning them a shared Nobel Prize for Chemistry in 1962 “for their studies of the structures of globular proteins”), and there are now more than 100,000 biological molecules in the PDB. This information includes common structural motifs, such as alpha-helices and beta-sheets, which had already been predicted by Linus Pauling. Around 90% of the data has been obtained using X-ray crystallography, in which a beam of incident X-rays is diffracted by atoms in the protein. By measuring the intensity and scattering angle of the diffracted beams, crystallographers can obtain a 3D picture of the density of electrons in the protein, and so work out the average position of each atom in the crystal. Most of the remaining 10% of structures in the PDB have been resolved using nuclear magnetic resonance spectroscopy, while a few structures have been solved by firing a beam of electrons through a cryogenically cooled sample, to yield a high-resolution image.
Bubbling up Microbiologist Tom Brock taking a sample from near a hot spring in Yellowstone Park, US, in the hunt for extreme bacteria. (Courtesy: Peter Menzel/Science Photo Library)
By comparing protein structures in the PDB, researchers have uncovered a myriad of adaptations that keep proteins stable and active under extreme conditions. For example, Michael Danson, a structural biologist at the University of Bath’s Centre for Extremophile Research, and co-workers have shown that heat-adapted (thermophilic) proteins tend to have a more tightly packed hydrophobic core and greater electrostatic interactions than their middling-temperature (mesophilic) counterparts. Cold-adapted (psychrophilic) proteins, in contrast, have a reduced hydrophobic core and a less charged protein surface, which may help them to stay flexible and active at low temperatures. Meanwhile, detailed studies by Oscar Millet and co-workers at the CIC bioGUNE lab, Spain, on salt-adapted (halophilic) proteins have shown that structures featuring amino acids with short “side chains” are preferred, as they reduce the interaction surface between the protein and the solvent. This is thought to be an advantage in an environment where water molecules are in short supply because so many of them are bonded to salt ions.
Among the other types of extremophiles, the pressure-adapted piezophiles are of particular interest to physicists. One of the first to study how proteins fall apart, or denature, at high pressure was Percy Bridgman, who won the 1946 Nobel Prize for Physics “for the invention of an apparatus to produce extremely high pressures and for the discoveries he made therewith in the field of high-pressure physics”. After subjecting an egg to a pressure of 7000 atmospheres, Bridgman found that the egg appeared as though it had been hard boiled in water – a discovery that fuelled interest in using high pressures to preserve food.
More recently, experimental studies have begun to probe the high-pressure limits on bacterial survival. For example, Paul McMillan and co-workers at University College London have found that the bacterium Shewanella oneidensis MR-1 can survive pressures into the gigapascal range – more than 10,000 times higher than atmospheric pressure at sea level. The survival mechanisms for such bacteria are not well understood, but new technologies may help. Nick Brooks and co-workers at Imperial College London, for example, are developing instruments to study the effect of high pressure on the structure and dynamics of biological systems. Their current projects include a device that makes it possible to carry out X-ray diffraction experiments at very high pressure, along with a platform for obtaining dynamic information under high pressure.
Folding into place
While we now know a lot about how the structures of proteins in extremophile organisms have adapted, we have less information (particularly quantitative data) on the conformational dynamics and flexibility of these proteins. An important area of study is what happens when proteins fold. Protein folding is a stochastic process by which a polypeptide chain transforms itself from a random coil into a characteristic and functional 3D structure.
Studying how proteins fold in extreme environmental conditions presents physicists with a wonderful opportunity to explore the balance of entropic and enthalpic components that govern protein stability
We are not yet able to predict the correct folded structure of a protein, or how it gets there, simply by looking at its sequence of amino acids. However, we do know that folding involves a delicate interplay between global geometry and local structure, and that it is induced by hydrophobic interactions between non-polar regions of the protein chain (as well as by other mechanisms such as hydrogen bonding). We also know that when a protein folds, it loses a lot of the entropy associated with the numerous possible conformations it could have. This loss of conformational entropy is balanced by the increase in the enthalpy that results when new bonds form, including hydrogen bonds and ionic interactions. Studying how proteins fold in extreme environmental conditions thus presents physicists with a wonderful opportunity to explore the balance of entropic and enthalpic components that govern protein stability.
1 Unravelling proteins from extremophiles Mechanically unfolding a hyperthermophilic protein (purple) and a well-characterized marker protein (yellow) using single-molecule force spectroscopy. (Reproduced from Biochemical Society Transactions43 179)
The advent of single-molecule force spectroscopy (SMFS) in the mid-1990s has helped to reveal the molecular mechanisms of protein folding. One common SMFS technique uses an atomic force microscope, with one end of the protein tethered to a gold surface, while the other end is attached to the tip of a small, flexible cantilever. As the tip is moved away, the protein stretches out and unfolds, and the cantilever bends. By measuring the cantilever’s deflection with a laser and photodetector, the force needed to unfold the protein can be calculated, and the size of this force reveals the protein’s mechanical stability. Force measurements can also be used with theoretical models to determine other properties of the protein, such as its stiffness.
SMFS experiments have provided remarkable insight into the mechanical stability of proteins, revealing details about the relationship between protein structure and stability, as well as directly measuring protein unfolding and folding kinetics. Thanks to this work, we can now probe the importance of non-covalent interactions to the mechanical and thermodynamic stability of extremophilic proteins, including in conditions that mimic those in which the extremophile organisms lived (high and low temperature, and solution pH).
At the University of Leeds, we have been using SMFS to manipulate a protein called TmCsp (commonly known as the “cold-shock protein”) that is found in a hyperthermophilic bacterium, Thermotoga maritima (figure 1). In measuring the forces required to unfold TmCsp at different temperatures, we have seen the protein’s spring constant drop as the temperature rises, reflecting the enhanced malleability of the structure. These findings actually run counter to the hypothesis that proteins from thermophiles should have rigid structures resulting from improved packing and increased numbers of ionic interactions. Instead, our experiments suggest that malleability may be an essential design feature of heat-adapted proteins – perhaps by giving the protein a way of recovering its structure under extreme high-temperature conditions. Further studies will seek to uncover more details of the “energy landscape” of folding in proteins from extremophilic organisms, and to understand the importance of intermediate stages in the folding process.
New frontiers for life
Outside the biological-physics lab, the hunt for new extremophiles continues. The exploration of Antarctica, for example, has revealed previously unknown areas of groundwater and subsurface liquid water, some of which may house new examples of extreme life. Specialist facilities such as the UK’s Boulby International Subsurface Astrobiology Lab – the world’s first permanent deep subsurface laboratory – also provide opportunities to complete experiments in extreme conditions. Each discovery gives us a clearer understanding of the conditions required for life and extends the limits of what we know is possible. Extremophile discoveries are also helping to fuel the search for life beyond our own planet. By advancing our understanding of how molecules and organisms respond to extreme environments, we also learn more about the potential habitability of other worlds – including Mars, which according to recent evidence may be home to flowing water.
Deep sea, deep cold Researchers look for life in extreme places, including under the sea using submersibles such as Alvin (left), and in Antarctica. (Courtesy: Chris Linder/Woods Hole Oceanographic Institution; Andrew Allen, Scripps Institute of Oceanography/J Craig Venter Institute)
Back here on Earth, studies of extremophiles and extremophile proteins may prove important for the development of new biomaterials. Designing materials that are thermodynamically and mechanically robust, yet are also malleable or rigid enough to suit particular applications, is a big challenge, and to fully exploit proteins as self-assembling components in such new materials, we will need to expand the toolbox of available proteins. Proteins from extremophilic organisms therefore present interesting opportunities for researchers seeking to engineer robust synthetic biological materials.
While the bacteria and their single-celled cousins, the archaea, are the true masters of extremes, as the field of synthetic biology continues to grow, we may eventually need to add a new domain to the tree of life. In creating such a domain – which has already been given a suggested name, synthetica – we can take inspiration from the many extremophiles that have been found in the bacteria and archaea domains, and perhaps some from our own domain, eukarya. Advanced techniques such as genome sequencing and super-resolution microscopy, as well as exploration of the macromolecular organization of the cellular machinery and collective motion, will undoubtedly shed light on the mystery of how extremophiles survive and adapt to some of the toughest conditions on the planet.
Physicists in Germany have steered beams of X-rays around corners by carefully shining them along extremely narrow channels carved into a thin layer of tantalum – a feat that had not been expected, given how X-rays are known to undergo optical refraction. The waveguides were able to deflect X-ray beams by up to 30°, and the team says that the thumbnail-sized devices might be used for ultrahigh-resolution imaging or for analysing pulses from free-electron lasers.
Building optical devices for light at X-ray wavelengths is extremely difficult because the index of refraction for X-rays in solid materials is slightly less than it is in air. This makes it difficult to send X-rays along waveguides such as optical fibres, which exploit total internal reflection. A ray of visible light travelling from glass to air is refracted away from the normal to a significant degree because the indices of refraction of glass and air are very different. This means that the light will reflect back into the glass waveguide, even when the beam is at relatively large angles to the air–matter interface. In contrast, X-rays need to be within about a thousandth of a degree of the interface to undergo total internal reflection.
Scientists have been able to make straight X-ray waveguides by very precisely shining a beam into a long, narrow channel of air cut into a medium such as silicon or a metal. However, the tiny difference in the refractive indices meant that no-one had tried to build a curved version.
Narrow and precise
Now, Tim Salditt and colleagues at the University of Göttingen have overcome this problem. They reasoned that an X-ray beam can be sent along a curved waveguide as long as the device is sufficiently narrow and the optics used to focus the beam sufficiently precise. When a beam enters a curved channel, the part of the beam on the inside of the curve is deflected through the greatest angle when bouncing off the far side of the channel (the outside of the curve). This means that the channel entrance must be made as narrow as possible to limit the beam’s maximum angle of deflection. On this basis, the team calculated the maximum width a waveguide could have if it is to transport a beam of a given wavelength through a given angle.
To put their idea to the test, the researchers used electron-beam lithography to carve out five curved channels on a 500 nm-thick tantalum “chip” measuring 5 × 5 mm. Each channel is 100 nm wide and the waveguides have radii of curvature of 10–80 mm. They placed the chip in a 1.5 nm-wavelength X-ray beam produced by the PETRA III synchrotron source at the DESY laboratory in Hamburg. The beam was fired into each waveguide in turn and the team measured the pattern of radiation emerging on the far side of the chip. The researchers found that they could transport a significant fraction of the beam’s intensity through quite large angles – over 18° in the case of the waveguide with 10 mm radius of curvature.
Emboldened by these results, they carved out a second chip on an identical-sized piece of tantalum but with the channels in this case having radii of curvature of 1–30 mm. They then placed this chip in a 1.5 nm beam produced at the European Synchrotron Radiation Facility in Grenoble, France. Although, as before, much of the beam leaked out along the way, a significant portion of it nevertheless made it to the end of the waveguide with the 10 mm curvature – turning through 30° in the process.
X-ray interferometry
According to Salditt, chips guiding X-rays through 30° could have a number of applications, including interferometers that split X-ray beams and then recombine them. Such devices could be used to measure the length of the very short pulses produced by free-electron lasers. Another possibility, he says, would be to direct X-rays to carry out very high-resolution imaging of objects such as living cells.
David Paganin of Monash University in Melbourne, Australia, agrees that curved X-ray waveguides could have a number of practical applications, and adds X-ray-based information processing and the probing of ultrafast molecular dynamics to Salditt’s list. “This development could be to X-rays what the optical fibre is to visible light,” he says.
According to Salditt, the waveguides could be made more efficient by covering the channels – currently they are open to the air above – and by replacing the tantalum with a material that absorbs fewer X-rays, such as diamond or beryllium. With the right combination of materials and beam wavelength, the team believes it may be possible to deflect X-rays through 90°, or even 180° for a waveguide having a radius of curvature of around 1 mm.
The photonics industry is a major contributor to the UK’s hi-tech economy. In 2012 (the most recent year for official statistics), the sector as a whole had an annual turnover of £10.5bn, and it employed more people than the country’s pharmaceutical industry. But that kind of status doesn’t develop overnight, and it doesn’t happen by accident.
That’s the message that comes across in this video, which was recorded at the University of Strathclyde’s Technology and Innovation Centre in Glasgow, Scotland. This £89m building was officially opened in July 2015 and now houses more than a dozen different groups, including the Centre for Microsystems and Photonics (part of Strathclyde’s engineering department), the Fraunhofer Centre for Applied Photonics (CAP) and the Institute of Photonics.
The last of these organizations was founded in 1995 to strengthen links between Strathclyde’s physics department and the photonics industry. In the video, you’ll hear Martin Dawson, director of research at the Institute of Photonics and head of the CAP, talking about how those academia–industry partnerships have developed within the cluster of photonics companies located in Scotland’s central belt. You’ll also hear Simon Andrews, executive director of Fraunhofer UK Research, explaining why such partnerships – and the government funding that supports them – are important for building and maintaining hi-tech industries.
Inspired by origami, researchers at Donghua University in Shanghai, China, have built self-folding paper from extremely thin sheets of graphene oxide. The new paper bends in response to light or heat, and can be made to “walk” on a surface and even turn corners. The material could be used in a range of applications, including sensing, artificial muscles and robotics.
Origami is the ancient Japanese art of paper folding, and can transform a lightweight flat material into a strong and flexible 3D object. Its principles have inspired engineers to design a host of structures including vehicle airbags, satellite components and artificial muscles.
Self-folding structures are especially useful when they can be programmed to fold and unfold by exposing them to an external stimulant such as light. Such structures contain an active material or materials that respond to these stimuli. These active materials are usually polymer-based, which means that they respond well to changes in temperature, solvent, humidity, electricity and light. However, such materials can also be unstable and difficult to fabricate.
Strong and flexible
Now, researchers led by Hongzhi Wang and Meifang Zhu at the College of Materials Science and Engineering at Donghua have used extremely thin graphene-oxide nanosheets as the building blocks for a self-folding paper. The paper is flexible and easy to manipulate, and has a high tensile strength.
The sheets are made of several layers of reduced graphene oxide (rGO), which is very stable and does not change shape in response to external stimuli. Self-folding is achieved by coating some parts of the rGO sheet with several layers of graphene oxide that contains the polymer polydopamine (GO-PDA).
Unlike rGO, the GO-PDA layers contain water molecules that have been absorbed from the surrounding air. When the material is heated using an infrared laser, some of the water is driven out of the GO-PDA layers, which causes them to shrink. The rGO layers do not shrink, however, and the result is a sharp bending of the sheet in places where GO-PDA is present. When the light is switched off, the GO-PDA reabsorbs water from the air as it cools and the sheet flattens out.
Helping hand
By carefully patterning sheets of rGO with GO-PDA, the team made simple paper robots that can move forwards and backwards (see video above). They could even turn corners, which is a first for such a walking structure. Self-folding was also used to make a “hand” that could grasp and hold objects five times heavier than its own weight.
“We can programme how this paper bends so we can make it walk and turn around, as well as fold into pre-designed shapes simply by applying light or heat to it,” Wang explains. “We believe our work will help in the development of next-generation industrial mechanical actuators that could be used in applications like wireless remotely controlled microrobots, microfluidic chemical analysis, tissue engineering and artificial muscles, to name but a few.”
Wang and Zhu are now busy trying to make smaller versions of their paper. “As the device scales down in size, especially to the nanoscale, its folding properties will change significantly,” says Wang. “We are therefore interested in developing a nanosized all-graphene origami structure.”
Nit picker: the cold plasma lice killer. (Courtesy: Fraunhofer IST)
By Hamish Johnston
Do your children have head lice again? Now you don’t have to comb their hair until your arm goes numb or cover their head with goop. Instead, you can zap them away using a plasma. I’m not suggesting that you put your child’s head into ionized gas that’s hotter than the Sun – it turns out that a “cold atmospheric pressure plasma” will do the trick.
That’s the claim of researchers at the Fraunhofer Institute for Surface Engineering and Thin Films in Göttingen, Germany. The team has created the above prototype, which creates a plasma using a high-voltage generator that sends short pulses to the teeth of the comb. The pulses ionize air molecules surrounding the teeth, but they are so short that the resulting plasma does not heat up. The charged ions and electrons in the plasma make short work of killing lice and their eggs, but are harmless to humans – at least according to Wolfgang Viöl and colleagues, who will be unveiling their device later this month at the MEDICA trade fair in Düsseldorf.
Tiny dust particles have been found floating more than 1000 km above the surface of Mars – about 10 times higher than planetary scientists had expected to find them. The particles were spotted by NASA’s MAVEN spacecraft, and their presence suggests that the red planet is accumulating dust from the solar system. The discovery could provide important clues about how dust moves around the solar system.
Scientists already knew that dust is lifted as much as 100 km from the surface of Mars by localized “dust devils” and global dust storms. Dust that is higher than about 150 km from the surface could come from the surface erosion of the Martian moons Phobos and Deimos. However, calculations suggest that this dust would enter the atmosphere via a doughnut-shaped ring around the planet – a ring that has not been detected by MAVEN.
Plasma clouds
The mysterious dust particles were seen by MAVEN as it follows a highly elliptical orbit of Mars, which varies in altitude from 150–6200 km. MAVEN began orbiting Mars in September 2014, and its Langmuir Probe and Waves (LPW) instrument detects dust by sensing the tiny plasma clouds that are created when dust particles strike the craft.
Because the entire surface of MAVEN acts as the detector, it can measure very low concentrations of dust. The size of each particle detected is estimated from the amplitude of its LPW signal, and the data were collected over seven months, which corresponds to more than 1000 passes to within 150 km of the Martian surface.
The data reveal a relatively constant concentration of dust particles from an altitude of about 1500 km down to about 500 km. At the lower heights, the number of particles increases rapidly, and is a factor of five greater at 150 km – the lowest altitude probed. Lab-based experiments suggest that the particles are about 1–12 μm in size, but the researchers cannot think of any known mechanism that could propel the dust from the surface to beyond a height of about 150 km.
Missing process
“If the dust originates from the atmosphere, this suggests we are missing some fundamental process in the Martian atmosphere,” says Laila Andersson, who is lead author on a paper in Science that analyses data from the LPW. Writing in the latest issue of Science, Andersson and colleagues reckon that the dust is interplanetary in origin and could be particles driven by the solar wind or debris brought into the inner solar system by comets.
If so, Mars will not be alone as a collector of interplanetary dust. The Earth’s atmosphere contains it too, and the team used previous measurements done on Earth to estimate how much interplanetary dust should be found on Mars. This calculation suggests that the LPW has only seen a small fraction of the interplanetary dust that could surround Mars.
Raving over MAVEN
Also in Science are three other papers reporting MAVEN results. The orbit of MAVEN was adjusted occasionally so that it dipped to within 120 km from the surface of Mars. These “deep-dip” campaigns took MAVEN to within the planet’s upper atmosphere, where Stephen Bougher of the University of Michigan and an international team measured the concentrations of gases including carbon dioxide, argon, nitrogen oxide and oxygen.
They found that the concentrations varied substantially from dip to dip, suggesting that the upper atmosphere is a dynamic place. The team also measured variations in the magnetic field of Mars from dip to dip. Its results suggest that both the crust of the planet and the solar wind contribute to the magnetic properties of Mars.
In another paper, Bruce Jakosky of the University of Colorado Boulder and colleagues describe how they used instruments on board MAVEN to work out how many ions escape from the Martian atmosphere during solar bursts. This information could help scientists to understand how a sizeable chunk of atmosphere could have been lost by Mars early in its history.
The final paper focuses on an aurora event that occurred in the planet’s northern hemisphere. Nick Schneider of the University of Colorado and colleagues used MAVEN’s Imaging Ultraviolet Spectrograph to study this Martian version of the northern lights, which they found to be more evenly distributed and diffuse than its terrestrial counterpart.
The four papers are published in a special issue of Science.
It being the International Year of Light, guests were also treated to two spectacular stage shows. Having just settled into our seats, we first watched as three dancers performed in front of lasers, dry ice and strobe lighting (see photo above) – certainly a first for an Institute awards dinner – while after the meal we were treated to a troupe called Feeding the Fish.
Their dancers carry laser batons to create “one-of-a-kind performances that fuse tight choreography with…specialized lighting effects”, with the batons being used to show everything from triangles and butterflies to even the logo of the Institute of Physics. Quite how it all worked certainly had physicists in the audience scratching their heads.
By examining the aftermath of the collisions of gold ions at close to the speed of light, an international team of physicists has measured the strong interaction between pairs of antiprotons for the first time. The researchers found that at very short distances, antiprotons – the antiparticles of protons – attract each other just as protons do. While this result was expected, it should improve our understanding of how antinuclei are held together. It also further strengthens the idea that charge, parity and time-reversal (CPT) symmetry is a fundamental symmetry of nature.
The strong interaction binds protons and neutrons together in atomic nuclei and it is also responsible for gluing together the quarks that make up protons, neutrons and other baryons. At very short distances, the strong force is attractive and much stronger than the electromagnetic force, which tends to push protons apart.
This latest experiment was carried out by the STAR collaboration at the Brookhaven National Laboratory’s Relativistic Heavy Ion Collider (RHIC). As well as showing that the force between antiprotons is attractive, the team was also able to measure two other important parameters – the scattering length and the effective range of the interaction.
It’s the mirror we think nature obeys Daniel Kaplan, Illinois Institute of Technology
Brookhaven’s Aihong Tang explains that the team expected the interaction to be CPT symmetric, which means that antiprotons behave as protons do. CPT symmetry means that if you switched the charge and parity of a particle and reversed time, all of the laws of physics would remain the same. “It’s the mirror we think nature obeys,” says Daniel Kaplan of the Illinois Institute of Technology in the US, who was not involved in the work. No experiments, to date, violate CPT symmetry, and physicists currently accept it as “an article of faith”, he adds.
It is not surprising that the researchers did not find CPT violations, Kaplan says, because the conventional wisdom states that if such violations existed, they should be much weaker than the strong force. This means that STAR will have to make much more precise measurements if it hopes to reveal violations. “It will be some super-small interaction, so weak that we haven’t noticed it before,” Kaplan says. “The strong force is the strongest force there is. If you imagine some new mechanism that causes a CPT violation that no previous experiments have ever seen, how can it be big enough to be a significant part of the strong force?”
Lamppost search
While the results are not groundbreaking, it is useful to have another experimental confirmation of CPT symmetry, Kaplan explains. He describes the hunt for CPT violations this way: “Suppose you lost your keys at night. Where would you look? A normal person would say ‘I’d look where I think I dropped them.’ But a scientist would say ‘Let’s look under the lamppost because there’s actually light there.’.” The STAR collaboration looked for CPT violations where it had at least a chance of seeing them.
Performing the measurement is a numbers game, Tang says. The teams derived the result by observing the signature of the antiproton–antiproton interaction in 500 million gold–ion collisions. The team also made a similar measurement of the proton–proton interaction. Antiprotons are difficult to produce, and because they annihilate with regular protons to produce photons, they do not hang around, either. Each collision at RHIC produces thousands of particles but only 3–4% of these are antiprotons.
Useful parameter
This latest result will also help physicists to understand how antinuclei are bound together. Such experimental measurements are useful in quantum chromodynamics (QCD), the theory that describes the strong interaction. It is difficult to use QCD to calculate the strong force purely from theory, and this measurement of the antiproton interaction can be used as a parameter in the calculation.
In addition, by studying how antinuclei are bound together, physicists could learn how to make heavier antimatter nuclei. Several types of antinuclei have already been produced. These include antitritium – which is one antiproton bound with two antineutrons, and antihelium-4, which is two antiprotons bound with two antineutrons. However, Tang says that physicists are still a long way from producing antimatter for any sort of practical use.
