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Loss of unregarded forests is at danger level

The world’s unregarded forests are at risk. Intact forest is now being destroyed at an annual rate that threatens to cancel out any attempts to contain global warming by controlling greenhouse gas emissions.

Trees in the tropical regions are dying twice as fast as they did 35 years ago – and human-induced climate change is a factor.

And a third study has highlighted the value to humanity of intact forests, while estimating that four-fifths of the Earth’s remaining woodlands are now in some way degraded by human activities. “This figure,” researchers warn, “is probably an underestimate.”

All three studies confirm the value of forests to the planet – and underline the increasingly dangerous rate of loss.

An international team of researchers report in Nature Communications that they made a computer model of the planet’s atmospheric conditions: they included natural and human-triggered aerosols, volatile organic compounds, greenhouse gases and other factors that influence temperature, one of which is albedo: the scientist’s word for the capacity of terrain to absorb or reflect solar radiation.

Cooling effect

They tested their model against the Earth’s temperature records since 1850 – and then ran it again, this time with a hypothetical forest-free world.

“The result was a significant rise of 0.8°C in mean temperature. In other words, today the planet would be almost 1°C warmer on average if there were no more forests,” said Paulo Artaxo, of the University of São Paulo in Brazil.

“If we go on destroying forests at the current pace – some 7,000 square kilometres per year in the case of Amazonia – in three to four decades, we’ll have a massive accumulated loss. This will intensify global warming regardless of all efforts to reduce greenhouse gas emissions.”

The second study, in the journal New Phytologist, is a reminder of just how complex the challenge of forest conservation can be. Foresters and botanists from around the planet concentrated on the special case of the tropical rainforest, home to so much of the world’s terrestrial biodiversity, and analysed the hazards.

These include rising temperatures, increasing carbon dioxide levels, fires, more destructive storms, insect infestation and the impact of woody vines known as lianas.

They found that trees in some areas were dying at about twice the rate they were 35 years ago.

“No matter how you look at it, trees in the moist tropics will likely die at elevated rates through the end of the century relative to their mortality rates in the past,” said Nate McDowell, of the US government’s Pacific Northwest National Laboratory.

“There is a host of factors that appear to be driving mortality, and the likelihood of those factors occurring is increasing.”

Such studies deliver no great surprises: they add levels of detail to a big picture that has been clearly outlined and repeatedly confirmed. Humans do not need to fell forests to find new farmland, and when they do so they damage the natural diversity on which they and other creatures depend.

Winners all round

Healthy forests absorb carbon dioxide from human fossil fuel combustion and at the same time reduce regional temperatures.

Forests are being destroyed at a disconcerting rate, but if humans conserved them, there would be a greater chance of containing global warming to targets set by a global climate summit in Paris in 2015.

And repeated studies have confirmed that conserved forests deliver many benefits. Everybody wins.

Just how humans benefit has been spelled out yet again in the journal Nature Ecology and Evolution. Forests cover about 25% of the planet’s land surface, but over the past three centuries Earth has lost at least a third of its natural tree cover, due to human expansion. More than 80% of what remains has been affected by human action.

Vital stabilisers

But these same forests absorb around 25% of carbon emissions from factory chimneys, power stations and car exhausts; they play a vital role in stabilising local and regional weather, and they reduce the risk of drought.

Intact forests are home to higher numbers of other species; they sustain many indigenous cultures; their conservation delivers medically-beneficial plants and their degradation drives the spread of infectious diseases.

“It is well-known that forest protection is essential for any environmental solution – yet not all forests are equal,” said James Watson, of the University of Queensland in Australia and the World Conservation Society.

“Forest conservation must be prioritised based on their relative values, and Earth’s remaining forests are the crown jewels, ones that global climate and biodiversity policies must now emphasise.” – Climate News Network

• This report was first published in Climate News Network

Resistive switches gain functionality on paper

Whether it’s alternative technology for non-volatile memory or computing architectures that mimic the brain, when it comes to next-generation electronics the chances are a resistive switch is at the heart of it. Now for the first time researchers have fabricated a device that allows resistive switching with both the large ratio between resistance states needed for memory and the small ratio used in neuromorphic computing. In addition the device is printed on cheap and flexible plain paper, and can be mechanically reset by bending.

When a nanoscale morphology is characterized by “high porosity”, “roughness”, and “poorly connected and non-compact structures” a lot of people steer clear. However, as Paolo Milani explains, granular materials with a lot of defects at the nanoscale can have very interesting behaviour. He began to consider the possibility of resistive switching behaviour in the cluster-assembled materials he was investigating at Universita degli Studi di Milano in Italy when Simon Brown – who specializes in resistive switching research at the University of Canterbury in New Zealand – came to Milan on his sabbatical.

Milani and his colleagues in Milan were the first to demonstrate the potential of “supersonic cluster beam deposition” (SCBD) for bottom up nanofabrication. The technique involves vaporizing and sputtering a target material that then forms a supersonic beam, which passes through an expansion chamber and onto the substrate. They were also looking at paper as a cheap substrate for printing flexible devices, so the next step was to combine the two.

Brown and Milani worked with students Matteo Mirigliano and Chloé Minnai, who did many of the experiments and was a key part of the collaboration between the two groups. When they printed gold devices on glass and silicon using SCBD they were able to switch between low and high resistance states that were comparatively close to each other when they applied and removed a voltage. However when they printed the devices on paper they found a threshold voltage at which they could reversibly switch the device into a state with a resistance several orders of magnitude greater than the lower resistance states, revealing two resistive switching regimes in the same device.

“We did not suspect that paper could support resistive switching at all,” says Milani. Further surprises were in store when purely by accident the researchers discovered after bending the device, that it was reset to the low resistance state. Milani knows no other reports of a device that can accommodate two switching regimes or mechanical reset of a nanoscale switch.

Monolayer resets record for thinnest non-volatile memory device

Nanocoherer

Mechanical resistive switching reset is known at the macroscale, in the coherer devices Guglielmo Marconi exploited when he first developed the radio telegraph system in 1894. Those devices consisted of a glass ampoule containing metal filings that would switch from an insulating to a conductive state when a voltage was applied, and reset after tapping. While the device worked reliably enough to transmit Morse code messages and form the basis of the telegraph system for over a decade, the mechanism behind the switching and mechanical reset was never fully understood. Shedding light on the mechanism behind the resistive switching in the paper device could also provide insights into the operation of Marconi’s coherer.

“We suspect it is the fibrous structure of the paper that allows the two regimes,” he suggests. “There may be interplay between the nano and the microscale structures that gives rise to the dual regime, but we are investigating this.”

The results could also have implications for applications of nanoscale resistive switching devices, since the same device could be used for both memory and for mimicking the synaptic connections in neural systems that allow learning. “This could help if you start to build up more complicated neuromorphic architectures,” says Milani. Although this is just the first stage, both the functionality and the efficiency of computers could greatly improve by mimicking the brain, which effortlessly handles complex tasks all day on just three meals, a million times less than the power conventional computers consume for equivalent output.

Predictive disorder

Despite the apparent disorder in the deposited gold, the SCBD printing approach allows for a great deal of control over the level of disorder through careful selection of the deposition parameters, and this determines the initial resistance of the system. The threshold voltage at which the system switches between regimes in turn depends on this initial resistance. Although the disorder has discouraged some people from working with this kind of system, as Milani emphasises it is not random but disorder that can be very precisely controlled.

“We start to recognize nanogranular systems present physics that is very interesting – this has not been recognized,” he adds. “Before people wanted to embed these structures or put a shell around. But it’s the same as it was with macrosocopic granular matter, which is important, but it was only in the 1980s and 1990s that this was recognized as something that could be described with a solid theoretical approach.”

As well as printing artificial devices that share behaviour with neurons, the team have also successfully grown natural neurons with their technology, opening up interesting possibilities of designing systems that combine natural and artificial neurons. First however Milani is keen to understand the basic principle behind their resistive switching device and achieve better control for more complex devices.

Full details are reported in Nano Futures.

New catalysts by design

A pioneering approach to designing and synthesizing catalysts for the hydrogen evolution reaction (HER) makes use of a technique called scanning probe block copolymer lithography (SPBCL) and density-functional theory calculations. The method could not only be used to produce more cost-effective alternatives to platinum-based catalysts for applications in fuel cells, but might even prove to be a completely new way to discover and make novel catalysts for almost any industrially important process, according to its inventors.

Designing efficient new catalysts is no easy task, especially when nanoparticles are the active structures. In catalysts that contain more than one element, for example, researchers not only need to take into account all the possible elemental combinations, they must also add a number of other variables, such as particle size, shape and surface structure, as well as the degree of alloying or phase segregation. This ultimately leads to an overwhelmingly large number of potential candidates.

To address this challenge, techniques to make poly-elemental particles and control their alloying or phase segregation state combined with screening methods to reduce their overall number need to be developed. Such techniques require combinatorial approaches coupled with theory calculations.

Combining SPBCL and DFT

A team led by Chad Mirkin, Chris Wolverton and Yijin Kang of Northwestern University in the US has now used an up-and-coming nanoparticle synthetic tool called scanning probe block copolymer lithography (SPBCL) combined with density-functional theory (DFT) calculations to explore three-component particles consisting of different combinations of platinum, gold, copper and nickel.

In their experiments, the researchers chose to study the hydrogen evolution reaction (HER) because it is crucial for commercially producing hydrogen in fuel cells. In an acidic electrolyte, the catalyst’s hydrogen binding energy (HBE) is the most important descriptor for the HER. According to the so-called Sabatier principle, the HBE of a HER catalyst should neither be too strong nor too weak – that is, the surfaces of the metals making up the catalysts should neither be too strongly nor too weakly absorbing.

Reducing the HBE

Although Pt is the best-known single-element catalyst for the HER, it could be further improved if its HBE was reduced. Electronically tuning its d-band structure by alloying it with another element, or indeed other elements, is a good way of doing this.

To find out which combinations of Pt, Au, Cu and Ni were best, Mirkin and colleagues studied the PtAu-M tri-metallic system (where M=Ni or Cu). They first used DFT calculations to calculate the HBEs of the different structures. They then synthesized these target structures using SPBCL and evaluated their catalytic properties. One of the advantages of SPBCL is that researchers can control the growth and composition of individual nanoparticles patterned on a surface, which allows them to produce particles that have uniform stoichiometry and phase.

Seven times more active

Thanks to these experiments, described in PNAS, the researchers identified PtAuCu as having the optimal calculated HBE and thus the highest measured HER activity – seven times more active than state-of the-art commercial platinum, says Mirkin.

“In addition to providing a new way to catalyze the HER, the paper highlights a novel approach for making and discovering new particle catalysts for almost any industrially important process,” says Wolverton.

“To find best-in-class materials that drive any application of interest, we need to identify ways to reduce the number of possibilities that will be studied and increase the rate at which they can be explored,” adds Kang. “This combination of theory and nanoscale particle synthesis begins to take on that challenge,” says Mirkin.

Quantum spin liquid could shed new light on superconductivity

A new type of quantum spin liquid has been unveiled by an international team of physicists and chemists. The technique for making the material was developed by Maarit Karppinen and colleagues at Aalto University in Finland, the Brazilian Center for Research in Physics (CBPF), Germany’s Technical University of Braunschweig and Nagoya University in Japan. It could lead to the creation of new and potentially useful high-temperature superconductors and materials for creating quantum computers.

Quantum spin liquids are in fact solid magnetic materials that are unable to arrange their magnetic moments (or spins) into a regular, stable pattern. This is unlike a ferromagnet, for example, in which all the spins point in the same direction or an antiferromagnet where neighbouring spins point in alternating directions. Instead, the spins in a quantum spin liquid are constantly changing direction in a fluidlike manner — even at temperatures close to absolute zero.

Idle speculation

This novel state of matter was predicted in 1973 by the future Nobel laureate Philip Anderson who tells Physics World, “It was a speculation that you could label as ‘idle’, in that I didn’t follow it up with much of anything”.

However, the discovery of high-temperature superconductivity in 1986 encouraged Anderson to follow-up his initial prediction. In 1987 he found a possible crucial link between quantum spin liquid theory and high-temperature superconductivity.

Today, high-temperature superconductors are sought for myriad applications, including energy grids, levitating transport and quantum computing. However, the physics underlying these materials is still poorly understood so the possibility of studying a real-life quantum spin liquid has piqued the curiosity of condensed-matter physicists including Anderson – who says “It’s fascinating that they keep turning up”.

To fashion a quantum spin liquid, Karppinen and colleagues ground and pressed a polycrystalline magnetic material with square lattice ordering into pellets. Then they modified the magnetic interactions of this square structure by adding tellurium and tungsten ions to the material – which introduced disorder.

To confirm they indeed had a quantum spin liquid on their hands, the team cooled their samples, revealing a characteristic dynamic magnetism all the way down to 19 mK. They used a number of different techniques, including muon spin spectroscopy, X-ray diffraction, SQUID magnetometry and many more, to support their claim of making a quantum spin liquid.

Square lattice

While quantum spin liquids have been produced before, almost all of them have a kagome structure – a lattice of corner-sharing triangles. This is unlike the material made by Karppinen and colleagues, which is the first quantum spin liquid to have a square lattice, which is also found in high-temperature superconductors.

As well as having the potential to shine new light on the physics of high-temperature superconductors, quantum spin liquids could be created specifically to harbour collective excitations (or quasiparticles) that could be used to store and process quantum information. These quasiparticles would be particularly useful because they would be topologically protected from being degraded by environmental noise.

Karppinen says that with further work “this research on quantum spin liquids can lead us to the experimental realization of the topological quantum computer”.

The new quantum spin liquid is described in Nature Communications.

Crystallography characterizes viruses in intact cells

Determining the structure of a virus without having to isolate it from cells first is the dream of many scientists. Helen Duyvesteyn and her colleagues from the University of Oxford, Diamond Light Source and the University of Helsinki are working to make this dream come true.

In their recent study (Scientific Reports 10.1038/s41598-018-21693-3), the researchers described how viruses grew and formed crystalline arrays inside cells. Thanks to the very bright signal of an X-ray free-electron laser (XFEL), they were able to obtain structural information about the viruses directly in the intact cell. Without the need to isolate viruses from the cells that they were grown in, they could avoid potential damage of the virus.

In living cells, viruses form crystals so small that only a microfocus beamline at a synchrotron or an XFEL laser can be used to study them. Of these two, the XFEL is over a billion times brighter, making it the more potent light source.

Analysing virus crystals within cells does, however, also decrease the signal-to-noise ratio, due to the contribution of other cell components. Moreover, the team recorded data using a jet stream of cells flying through the XFEL beam, with images taken at fixed time point – no matter whether there was a cell with viral crystals in the beam or not. This resulted in the recording of thousands of images, from which the ones containing relevant information had to be extracted.

Separating the wheat from the chaff
The researchers realised that images containing the valuable diffraction patterns were all less than 0.3 MB in size. This is because jpeg files compress in size depending upon the information content of the image. Based on this finding, they were able to discard 72% of the images recorded. To ensure that no information was lost, the researchers manually checked a large number of the discarded images and, indeed, found no diffraction patterns on any of them. Of the remaining smaller images, 7.2% showed diffraction patterns. This represented 680 images – and the researchers then recorded every single spot on each one by hand.

The resulting data indicated that the particles in the crystals were so-called procapsids, empty virus shells that contain no DNA. Four virus particles were found per 500 Å. While the obtained data were not of high resolution, the experiments showed that in cellulo crystallization of viruses holds promise for studying viruses without having to isolate them. The authors also hope that their proof-of-concept experiments will enable the investigation of viruses that can only be studied inside living cells.

Many parameters to optimize
Duyvesteyn and her colleagues identified a number of factors that could be improved in the future to obtain better data. A 100-fold improvement of the signal-to-noise ratio can be achieved by optimizing the size of the jet of fluid delivering the cells to the beam of light, and a 25-fold improvement by optimizing the size of the light beam. Alternatively, a method called acoustic droplet ejection technology could be used instead of a fluid jet to deliver the cells into the laser beam.

MEG in motion: a wearable brain scanner

Magnetoencephalography (MEG) enables allows direct imaging of brain activity by measuring magnetic fields generated at the scalp by neural currents. MEG is currently performed using an array of cryogenically-cooled superconducting quantum interference devices (SQUIDs) placed in a one-size-fits-all helmet. Such systems, however, are cumbersome and highly sensitive to head motion – even a 5 mm movement can make the images unusable. As such, they rely on compliant adults who can remain still inside the scanner.

Now, a research team from the University of Nottingham and University College London has developed a wearable MEG system that can record brain activity at millisecond resolution while a subject is moving. The prototype headset opens up new possibilities for scanning any patient group, including infants or patients with movement disorders, and subjects who are free to move and interact with the real world (Nature doi: 10.1038/nature26147).

The system is based on an array of optically pumped magnetometers (OPMs) – magnetic field sensors that can record biomagnetic signals without needing cryogens. Each OPM sensor contains a glass cell containing ⁸⁷Rb vapour, heated to about 150 °C. A 795-nm laser beam is used to spin-polarize the atoms, and the intensity of light transmitted through the cell is detected using a photodiode.

In zero magnetic field, the spin magnetic moments align with the beam, and transmission of laser light is maximized. However, the presence of a magnetic field perpendicular to the beam causes a measurable drop in light transmission. The sensors have a noise level comparable to that of a SQUID and a dynamic range of ±1.5 nT.

The researchers created a prototype system comprising an array of sensors mounted in a 3D-printed helmet designed using an anatomical MRI scan of the subject’s head. They note that, although the glass cells are heated, the sensors’ external surfaces remain close to body temperature and can thus be placed directly onto the scalp. The lightweight helmet contains 13 OPM sensors mounted on the scalp over the right sensorimotor cortex, and four reference sensors placed close to the head to measure background interference.

Although the wearable MEG system is housed inside a magnetically shielded room, it is still essential to cancel out the remnant Earth’s field. To do this, the team constructed a set of bi-planar electromagnetic coils that generate fields equal and opposite to the remnant Earth’s field. The coils – designed on two 1.6 m² planes, placed either side of the subject – achieved a 15-fold reduction in the remnant field.

The researchers recorded OPM measurements with and without field nulling and saw that, without field nulling, the OPM sensors saturated during head movement. With field nulling, however, the OPMs could capture MEG data even while the head was moving.

High performance
To test the prototype OPM-MEG system, the researchers measured electrophysiological activity in a subject’s right sensorimotor cortex during visually cued finger motion. This task elicits a reduction in endogenous beta band oscillations during movement and a rebound when the movement stops. Such “beta modulation” is used as a marker of brain plasticity, psychosis and white matter degradation.

The experiment comprised 50 trials, of 1 s of finger abduction and 3 s of rest. Each subject performed the experiment 12 times: six during which they kept as still as possible, and six during which they made natural head movements, such as nodding, stretching, drinking tea and even playing ping pong.

OPM-MEG performed consistently across experiments, with the characteristic beta decrease and rebound clearly delineated and localized to the sensorimotor cortex. Despite head movement of more than ±10 cm, the team saw no significant difference in signal-to-interference ratio between the moving and static runs. Comparison with static experiments recorded using a cryogenic MEG system showed that the spatial resolution of the OPM system was better than that of the cryogenic system.

“This new technology raises exciting new opportunities for a new generation of functional brain imaging,” said Matthew Brookes, who leads the MEG work in Nottingham. “Being able to scan individuals whilst they move around offers new possibilities, for example to measure brain function during real world tasks, or genuine social interactions. This has significant potential for impact on our understanding of not only healthy brain function but also on a range of neurological, neurodegenerative and mental health conditions.”

Edinburgh Biosciences on a mission to restore sight

Edinburgh Biosciences, based in Livingston, Scotland, is on a mission to revolutionize the diagnosis and treatment of cataracts. Millions of people have cataract surgery every year and the benefits of developing a non-invasive, light-based procedure are compelling both for patients and healthcare providers.

As well as providing a quantitative diagnosis of the severity of visible cataracts, photonic tools being commercialized by the talented team of physicists, engineers and biochemists at the firm could warn of the condition in its early stages. The small-footprint spectrometers, designed in-house, feature compact light-emitting diodes (LEDs) and pave the way for gentle photo-bleaching of cataractous material as an alternative to surgery.

Edinburgh Biosciences believe that it is the first company to show that blue LEDs have the potential to replace more expensive, bulky and powerful lasers for rejuvenating cataractous eyes. The company has filed a patent application to register its claim (PCT/GB2016/053780).

We’re preparing to begin preclinical testing on complete living eyes, which will be a major step forwards in the programme.
Alan Kerr, chief scientist at Edinburgh Instruments

Lab tests on non-living lenses revealed that characteristic spectral transmission can be recovered using 430 nm fluorescence emission excited by a UV LED. Measurements also showed that light scattering is reduced in the treated specimens, which experts attribute to the reduction in the misfolded protein aggregates responsible for a cataract’s milky appearance.

It has been estimated that cost of conventional cataract operations worldwide could amount to more than £6 billion each year. Easy-to-operate LED-based units have the potential to deliver considerable savings by bringing the treatment to high-street opticians, minimizing the need for hospital visits and reducing the burden on the healthcare system. Because the instruments are portable and easily packed into a suitcase, they could play a huge role in providing eye care to the world’s population, whatever their location.

Technology development

Edinburgh Biosciences was formed as part of Edinburgh Instruments – a leader in spectroscopic instrumentation and gas detection solutions – to pursue biological applications of fluorescence spectroscopy. In 2011, the group’s R&D division was instrumental in the development of a novel interference filter together with partner company Delta Optical Thin Film of Denmark. The resulting wedge-profiled combination of optical coatings, which measures just a few centimetres in length, offers an elegant way of selecting precise colours (or wavelengths) of light from a beam passing through the filter.

An ultracompact solution, the filter’s spectral properties vary continuously along its length and allow instrument makers to miniaturize their designs. To give an example, when used with an LED light source, a linear variable filter can reduce the volume of a fluorescence spectrometer by more than 90%. The component’s development represents a key element in the Edinburgh Biosciences backstory, but it’s not the only one.

A major trigger for focusing on cataract diagnosis and treatment was a meeting between Professor Baljean Dhillon – Scotland’s only Professor of Clinical Ophthalmology and a consultant surgeon at Princess Alexandra Eye Pavilion in Edinburgh – and Desmond Smith, the founder of both Edinburgh Biosciences and Edinburgh Instruments. Smith, who was being treated for cataracts, was asked how he could use his photonics knowledge to advance eyecare. The discussion drove research into a quantitative tool that could help surgeons to determine more precisely the severity of a patient’s cataracts.

International network

Motivated by the prospects of photo-bleaching as a non-invasive method for treating cataracts, Edinburgh Biosciences initiated and led a EURO 2.6 million European Union project dubbed CATACURE to explore the technology in more detail. The programme ran from the beginning of 2014 to the end of 2016 and involved six partners across four European countries. Joining Smith and his team on CATACURE were experts from Glostrup Eye Hospital in Copenhagen, St Eriks Eye Hospital in Stockholm, Delta Optical Thin Film, HiTech Prontor of Germany and Heriot-Watt University, which is near Edinburgh Biosciences’ current facility.

“Building a strong network of partners is extremely important and we’re very excited by the results we’ve seen so far,” comments Smith. The company’s founder is a strong believer in the technology’s prospects and is backing the firm with his own money, thanks to the proceeds from the sale of Edinburgh Instruments to TECHCOMP EUROPE. Wai Shing Chen, a director of TECHCOMP, is also an early investor in Edinburgh Biosciences.

Buoyed by the success of the demonstrator unit, Edinburgh Biosciences is working towards its first human trials towards the end of 2019. It’s a busy time for the team. “Currently, we’re preparing to begin preclinical testing on complete living eyes, which will be a major step forwards in the programme,” says Alan Kerr, chief scientist at the company.

Market push

In 2018 the Scottish firm is looking to step up its push to market, which includes opportunities for new partners and investors. The company’s ultimate goal is to supply a combined diagnostic and non-invasive treatment tool for cataracts based on the successful CATACURE demonstrator. Core elements of the device also lend themselves to products in their own right.

A computer-controlled laser attenuator based on the novel linear optical filter is available to purchase now, and the product roadmap includes a wavelength selector followed by a miniature spectrometer. A fluorescence scanner for screening surgical instruments – a successful collaboration with the University of Edinburgh and one of the company’s first R&D products – also represents another revenue opportunity for this ambitious and talented firm.

Visit the Edinburgh Biosciences website for more details, and to get in touch with the team.

Amyloid fibrils undergo liquid-crystalline phase transitions

The class of liquid-crystalline phases known as cholesteric phases can form in amyloid fibrils in the same way as other filamentous biological colloidal systems, such as viruses, cellulose and oligo-DNA, according to new work by researchers at ETH Zurich in Switzerland. Amyloid fibrils are chiral protein-based systems and are very important in biology and medicine, but they are also emerging as promising building blocks for bionanotechnology applications. The new finding could help us better understand the role that these fibrils play in living organisms. The fibrils themselves could help inspire new materials that mimic biological structures and be used to make cholesteric liquid-crystal displays and advanced photonic devices.

“We also discovered that these fibrils undergo a liquid-crystalline transition from the untwisted, regular nematic to cholesteric phases, depending on the volume of the liquid-crystalline droplet,” says team leader Raffaele Mezzenga. “The chirality of the fibrils also inverses from left to right handedness as they go to the cholesteric phase. This behaviour is quite different from that of all other classes of biological filamentous chiral colloids in which the chirality evolves in the opposite way, that is, from right-to-left, or not inverted at all (right-to-right, for example).”

Chirality or handedness is ubiquitous in nature and plays a critical role in biology, medicine, physics and materials science. It refers to a property of structures that exist in two versions – “enantiomers” – that are mirror images of each other but cannot be superimposed. Natural chirality is highly selective and shows distinct preferences. “For example, only D-sugars are included in the formation of DNA, and only L-amino acids in the formation of proteins,” says Mezzenga. “This molecular chirality transfers in a way to control both structure and biological function.”

Experiments on such systems may lead to a better understanding of the mechanisms behind chirality transfer and therefore directly impact on the design of new materials that mimic biological structures, he adds.

Cholesteric phases in amyloids

Amyloid fibrils form into twisted ribbon-like structures through the self-assembly of beta-sheet aggregates. Pathological amyloids are often found in patients with neurodegenerative diseases such as Parkinson’s or Alzheimer’s while functional amyloids are crucial for physical and biological function in living organisms. Researchers are now discovering that they may be used as versatile platforms for making new functional biomaterials too.

Until now, no one had ever seen any chiral colloidal liquid-crystalline phases, also known as the cholesteric phase, in these fibrils. “This was rather puzzling,” says Mezzenga, “because the fibrils have a well-defined chirality at the single fibril level – as do other filamentous biological systems such as DNA, collagen or nanocellulose. Here such chiral nematic phases are regularly observed.

“We spent a lot of time hunting for these cholesteric phases in amyloids, trying out a number of approaches,” he explains; “What finally worked in the end was to break down the amyloids into smaller pieces and then search for the cholesteric droplets at compositions that are predicted by thermodynamics calculations.

Extremely rich phase diagram

“Apart from the unconventional chiral switch pathways (left to right handedness as opposed to the other way around), these systems boast an extremely rich phase diagram in which we can identify at least three types of liquid-crystalline droplets. The cholesteric phase is only one of these three classes. Such rich phase behaviour is unprecedented within a single system.”

The researchers used energy functional theory to try and help explain their results. “We expanded theoretical treatments developed for non-chiral nematic droplets, to the case where the colloidal rods are chiral and thus can undergo collective twisting behaviour,” Mezzenga tells nanotechweb.org. “The extended theory we developed allows us to explain many of our observed experimental findings.”

As well as furthering our fundamental understanding of chiral transfer and helping to develop new materials that mimic biological structures, the new work could have practical applications. “Cholesteric droplets selectively interact and reflect light that is circularly polarized as opposed to normal polarizers that only interact with linearly polarized light,” explains Mezzenga. “This very appealing characteristic might be exploited in cholesteric liquid-crystal displays (ChLCDs) that could be operated with virtually no power. Another immediate possibility is to make photonic devices in which combinations of colours are produced by the combined effect of photonic bandgap and cholesteric liquid-crystal reflection.”

Surface anchoring effects?

This is a very interesting article, comments Rik Wensink of the Laboratoire de Physique des Solides at CNRS and Université Paris-Sud, who was not involved in this work. “The observations hint at a subtle role played by surface anchoring effects in stabilizing cholesteric order in these systems, which is not yet fully understood.”

So, where next? “There are many areas that we are currently exploring,” says Mezzenga. “For example, we are still trying to understand other features of these amyloid cholesterics that are still not completely clear and trying to determine how different parameters affect their overall liquid-crystalline order.”

The research is detailed in Nature Nanotechnology doi:10.1038/s41565-018-0071-9

Importing meat may keep rivers clean

Mmmm – crispy bacon and pancakes for breakfast; but first the dilemma. British bacon or Dutch? Which has the least environmental impact? When it comes to rivers, the Dutch bacon may well be the better option. A new study has shown that some rivers are far more capable of mopping up livestock-related pollution than others. For countries, like the UK, with rivers that are already overloaded, imported meat helps to keep rivers clean at home, but often results in extra river pollution elsewhere.

Intensive livestock farming is a major source of organic pollution. Discharge of farm effluents, rich in organic pollutants, reduces biodiversity in rivers and disrupts aquatic ecosystems by depleting oxygen levels. Over the last 50 years, meat production has increased rapidly, and the upward trend is only likely to continue due to population growth, urbanization and increased income. So what kind of future do the world’s rivers face, what impact is globalization having, and which rivers are already at breaking point?

To answer these questions, Yingrong Wen, from Delft University of Technology in The Netherlands, and her colleagues used global livestock trade figures to calculate the biological oxygen demand associated with pig, chicken and cattle meat for each country. Livestock farm maps identified which river catchments pollution would run-off into, and a hydrological model estimated the amount of organic pollution that each river would receive, taking into account local weather conditions, river flow rates and the level of water treatment in each country.

Immediately the team saw that some countries, including Russia, Japan, Saudi Arabia, Mexico, Hong Kong, Italy and the UK, are heavily dependent on imported meat products, and would suffer a significant increase in river pollution if forced to produce meat locally. Meanwhile, major exporting countries like the US, Brazil, The Netherlands, Australia, Belgium and France must process more organic pollution than their fair share, due to their large meat export markets.

Surprisingly, more livestock farming didn’t always mean dirtier rivers. “Increases in organic pollutant loading do not always translate into more pollution,” said Wen, whose findings are published in Environmental Research Letters (ERL). “We found that rivers in eastern Australia, New Zealand and the Philippines had high enough cleaning capacities – dilution and natural degradation – to assimilate the increased loading.”

But some countries, like the UK, are already at capacity when it comes to river pollution. The results show that despite advanced wastewater treatment techniques, UK rivers would be overwhelmed if livestock farming was to increase. Instead the UK benefits by importing meat, offloading the environmental degradation to countries such as The Netherlands.

Meanwhile, nations that export a large quantity of meat, like The Netherlands, manage their pollution by concentrating livestock farming along particular river segments. This makes it easier to capture the pollution before it reaches the river. But for some countries this form of intensive farming isn’t an option. “Although Russia possesses extensive natural resources, the climate means that livestock farming is limited to the west,” said Wen. Farms must be widely distributed here as the quality of land is poor and can’t support large numbers of animals.

Studies like this show how important it is to quantify the impact of livestock farming on a river by river basis. “It is the actual pollution level in the river that matters, rather than how much pollution enters the river,” said Wen. “The same pollutant load will result in different pollutant levels depending on local conditions – river discharge and natural degradation rates, for example – which may vary significantly within a country.”

Europe picks exoplanet mission for launch

The European Space Agency (ESA) has announced it will launch the first probe dedicated to studying the chemistry of exoplanet atmospheres. Costing €450m, the Atmospheric Remote‐sensing Infrared Exoplanet Large‐survey (ARIEL) mission will launch in 2028 and will observe 1000 exoplanets over a four-year period.

ARIEL beat off two other missions vying for ESA’s latest “medium-class” launch slot. One was the Turbulence Heating Observer, designed to study the interaction of the solar wind with Earth’s magnetic field. The other was the X-ray Imaging Polarimetry Explorer to investigate X-ray emissions from high-energy sources such as supernovas, galaxy jets, black holes and neutron stars.

ARIEL will be launched from French Guiana by an Ariane 6-2 rocket and will be placed at Lagrange Point 2 – a gravitational balance point some 1.5 million kilometres beyond the Earth’s orbit around the Sun. The location will also be home to the James Webb Space Telescope, which is currently set to launch in 2019.

Ariel is a logical next step in exoplanet science
Günther Hasinger

From there ARIEL will study exoplanets that range in size from Jupiter to Earth focussing on hot planets that are in orbits close to their stars. Such intense temperatures keep molecules circulating in the atmosphere and stop them forming cloud layers where they are harder to detect remotely. ARIEL’s 1.1 x 0.7 m primary mirror will collect visible and infrared light while its spectrometer will determine the various gases in a planet’s atmosphere. A photometer will capture information about the presence of clouds and help to point to the target star with high precision.

“Although we’ve now discovered around 3800 planets orbiting other stars, the nature of these exoplanets remains largely mysterious,” says astronomer Giovanna Tinetti from University College London, who is ARIEL’s principal investigator. “ARIEL will study a statistically large sample of exoplanets to give us a truly representative picture of what these planets are like. This will enable us to answer questions about how the chemistry of a planet links to the environment in which it forms, and how its birth and evolution are affected by its parent star.”

Understanding Earth’s place in the universe

ARIEL has been developed by a consortium of over 60 institutes from 15 countries belonging to ESA. “Ariel is a logical next step in exoplanet science, allowing us to progress on key science questions regarding their formation and evolution, while also helping us to understand Earth’s place in the universe,” says Günther Hasinger, ESA’s science director.

ARIEL will now join a number of dedicated exoplanet missions that will launch in the coming decade. Next month, NASA is expected to launch its Transiting Exoplanet Survey Satellite, which will survey the brightest stars near the Earth for exoplanets over a two-year period. ESA, meanwhile, will launch a small mission to study exoplanets – Characterising Exoplanet Satellite – later this year as well as an exoplanet observatory, dubbed Plato, in 2026.

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