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Humans drive sixth mass extinction wave

About one million of the world’s animal and plant species are now at risk of extinction − the largest number in human history ever to be facing the threat of oblivion, scientists say. Many species could be wiped out within decades. And their plight is caused by humans, and will inevitably affect us too.

The warning was delivered by a British scientist, Professor Sir Robert Watson, chair of the UN’s Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES), speaking in the French capital, Paris.

He told an IPBES meeting held to approve the summary of its new global assessment report on the state of life on Earth that the implications for human life were grave. The overwhelming evidence gathered in the assessment presented “an ominous picture. The health of ecosystems on which we and all other species depend is deteriorating more rapidly than ever.

“We are eroding the very foundations of our economies, livelihoods, food security, health and quality of life worldwide.”

But Professor Watson, a previous chair of the UN’s Intergovernmental Panel on Climate Change (IPCC), does not preach despair. Despite the “truly unsustainable rate” of species loss that would affect human wellbeing for this generation and for its descendants, despite the accelerating pace of extinction, he believes there is still hope.

“We are in trouble if we don’t act, but there are a range of actions that can be taken to protect nature and meet human goals for health and development. It is not too late to make a difference, but only if we start now at every level from local to global.” Transformative change, system-wide and including goals and values, could allow humankind to restore nature and to use it sustainably, he said.

In an unusually forthright challenge to individuals, businesses and governments which continue to question or ignore the findings of science in pursuit of their own interests, Professor Watson, a globally-renowned environment scientist, acknowledged that that sort of change “can expect opposition from those with interests vested in the status quo”. Such opposition “can be overcome for the broader public good”, he added.

The assessment report’s findings make spine-chilling reading. It says the average abundance of native species in most major land-based habitats has fallen by at least 20%, mostly since 1900. More than 40% of amphibians and more than a third of all marine mammals are threatened. The picture is less clear for insects, but available evidence supports a tentative estimate of 10% being threatened.

Global impact

“The essential, interconnected web of life on Earth is getting smaller and increasingly frayed,” said Professor Josef Settele, one of the co-chairs of the global assessment, of the Helmholtz Centre for Environmental Research in Germany . “This loss is a direct result of human activity and constitutes a direct threat to human well-being in all regions of the world.”

The summary says there are five main causes of the crisis. In descending order they are: changes in land and sea use; direct exploitation of animals and plants; climate change; pollution; and invasive alien species.

It adds plenty of detail:

• Three-quarters of the land-based environment and about 66% of the marine environment have been significantly altered by human actions. On average these trends have been less severe or avoided in areas held or managed by indigenous peoples and local communities.

• More than a third of the world’s land surface and nearly 75% of freshwater resources are now devoted to crop or livestock production.

• Raw timber demand has risen by 45% and approximately 60 billion tonnes of renewable and non-renewable resources are now extracted globally every year – having nearly doubled since 1980.

• Land degradation has reduced the productivity of 23% of the global land surface, up to US$577bn in annual global crops are at risk from pollinator loss, and 100–300 million people are at increased risk of floods and hurricanes because of loss of coastal habitats and protection.

• Since 1980 plastic pollution has increased tenfold.

• Since 1992 urban areas have more than doubled.

• In 2015, 33% of marine fish stocks were being harvested at unsustainable levels.

Numbers unknown

Scientists point out that unlike the five earlier great waves of extinction to have occurred on the planet, this one is human-driven. IPBES has explained simply and clearly that humankind and its activities are responsible for what is happening, and that we shall have to pay the price.

IPBES has also succeeded in diagnosing the extent of the crisis overwhelming the natural world with a new degree of precision, despite the fact that nobody can say with any certainty how many species the Earth contains.

The Paris meeting approved the 40-page summary of the full IPBES report, which will be published later this year. At the end of 2020 two conferences, on the natural world and climate change, will provide global leaders with an opportunity to make specific plans for action.

Extinction Rebellion (XR), the group whose protests in April brought traffic in parts of London to a halt for a week and which is active in several other countries as well, is known for its vociferous demands for steps to tackle climate change.

It is careful to spell out its insistence that climate change and the fate of the natural world are twin threats, of equal gravity and urgency.

This article first appeared at Climate News Network

Microfluidics enters a new field

For years, the concept of “lab-on-a-chip” has fueled designs seeking to create miniaturized devices capable of performing a whole set of laboratory functions in the palm of your hand. While past efforts have struggled to effectively control liquids and materials on the micro-scale, a new device published in the Proceedings of the National Academy of Sciences offers a different approach to fluid manipulation. Following several years of collaboration, the team led by Govind Kaigala at IBM Research-Zurich and the group of Moran Bercovici at Technion-Israel Institute of Technology have now demonstrated that the key to dynamic control of fluid mechanics may be surprisingly electric.

The electric effect

Conventional techniques for guiding the microscale flow of fluids often rely on mechanical solutions, such as directly carving channels into polymers or glass. Although valves are sometimes added in order to dynamically control routing, the geometries of these systems are fixed, limiting them from attaining the true “lab-on-a-chip” goal of being able to perform multiple different experiments on one platform. More recent approaches have tried chemically modifying the chip’s surface to create a pattern of electric charge that dictates the path of a fluid; however, like the mechanical channels, the charge patterns are fixed and do not offer flexibility.

To control the motion of fluid in a way that is truly adjustable, the research team turned to electric fields. When liquid contacts a surface, it develops a layer of charge; applying an electric field to this layer moves the charges, dragging the liquid with them and creating a net flow. Taking advantage of this effect, the team designed a device that uses disk-shaped electrodes embedded in the bottom of a fluidic chamber to generate dipole-like flow patterns in the liquid when an electric field is applied. Placing multiple electrodes together in an array creates “virtual channels” that guide the fluid stream.

Outstanding in her field

“Each electrode acts as a virtual micro conveyer belt whose directions and intensities can be controlled electronically,” says Federico Paratore, lead author of the work, “As a fun example, we showed that we can bend an otherwise straight streamline into a sine wave, and then change its phase with a click of a button—it’s like looking at an oscilloscope signal, but where the signal is made of liquid!”

Discovery of new flow patterns

Besides redirecting a streamline through different virtual channels, the researchers created new flow patterns that have not been previously observed. For instance, they used a ring-shaped electrode configuration to create an inner region of stagnation surrounded by an outer region of flow, which could be used as traps for cells and particles, or as “virtual vials” for performing chemical reactions. By changing the voltages on the electrodes, they could then invert the pattern to create an inner region of flow surrounded by an outer region of stagnation, which is useful for selective on-demand mixing. While more applications of these flow patterns have yet to be explored, the control and flexibility the team’s device offers suggest that the lab-on-a-chip dream may finally be within grasp.

Batteries for electric vehicles, advances in radiotherapy, squid-inspired blankets

In this episode of the Physics World Weekly podcast, Anna Demming reports back from an event at the Society of Chemical Industry in London that focused on developing a supply chain in the UK for manufacturing the batteries that will be needed to create fleets of electric vehicles.

Tami Freeman talks about her visit to the European Society for Radiotherapy and Oncology in Milan, where she discovered what medical physicists think will be the most important issue for training new colleagues ten years from now.

James Dacey is also on hand to explain how the skin of a squid has inspired a new type of space blanket.

This was edited 30th May 2019 to correct the name “Society of Chemical Industry”

Single-atom imaging could help search for neutrinoless double beta decay

A new technique to enable the detection of a hypothetical process called neutrinoless double beta decay has been developed by an international team of physicists. Their technique involves probing a large sample of xenon for nuclei created by the decay process. If neutrinoless double beta decay is indeed spotted, it could have profound consequences for our understanding of the universe.

One of the central questions in particle physics is whether neutrinos are their own antiparticles. If they are, neutrinoless double beta decay – which is forbidden by the Standard Model of particle physics – should be possible. Several experiments are therefore competing to detect or rule out this exotic decay, which is predicted to be extremely rare.

Beta decay covers a family of processes that involve the emission of neutrinos (or antineutrinos) by a nucleus. One common beta-decay process involves a neutron in a nucleus transforming to a proton by the emission of an electron and an electron antineutrino. If neutrinos are there own antiparticles, the emitted electron antineutrino can then be absorbed as a neutrino by another neutron in the nucleus – leading to a second beta-decay and emission of another electron. While there is no overall emission of neutrinos, the nucleus has undergone a double beta decay and is left with two additional protons.

Explaining neutrino mass

Neutrinos being their own antiparticles could help explain why neutrinos have mass – something that is not explained by the Standard Model of particle physics. “We have to find mechanisms to generate neutrino mass,” explains theoretical particle physicist Werner Rodejohann of the Max Planck Institute for Nuclear Physics in Heidelberg: “The vast majority of these mechanisms predict neutrinos to be their own antiparticles.”

Rodejohann continues, “In the Standard Model without neutrino mass, you would have the same amount of matter and antimatter produced in the early Universe. These would then have annihilated leaving a Universe with only radiation. But since we are here, we know that something must have allowed a small asymmetry between matter and antimatter. Seeing neutrinoless double beta decay would confirm a lot of our ideas about how something survived.” Observing this, however, is extremely difficult.

The Enriched Xenon Observatory (EXO) in New Mexico looks for neutrinoless double beta decay in 200 kg of liquid xenon enriched in xenon-136, which is a neutron-rich nucleus that is considered a prime candidate for the process. The idea is that the two high-energy electrons emitted in the decay process ionize other xenon atoms, producing an electron shower that can be detected.

Search for barium

One challenge facing EXO physicists is how to distinguish these exceedingly rare events from other types of radioactive decay that can also produce a shower of electrons. The solution, according to William Fairbank of Colorado State University and colleagues, is to look for the barium-136 nucleus that is produced by the double beta decay of xenon-136. “None of the other likely background decays would produce a barium-136 atom at the decay site,” he explains.

Fairbank and colleagues have therefore developed a technique to retrieve single barium ions from a tank of liquid xenon using a cryogenic solid xenon probe with a small sapphire window on the end. They showed that barium ions can then be identified using laser spectroscopy. The researchers suggest that further development of the technique may provide a means to suppress the background signal in their next experiment – which will be called nEXO and will contain five tonnes of enriched xenon.

Another challenge facing the researchers is that xenon-136 in known to undergo conventional double beta decay. This is an extremely rare process that produces two electrons and two antineutrinos. Identification of a barium ion would prove only that double beta decay had taken place, not that it was neutrinoless. To further discriminate between the two processes, the energy of the emitted electrons must also be measured to work out if some energy has been taken away by the two neutrinos. The researchers calculate that, in the energy range of interest, there is about a 50% chance of detecting a two-neutrino double beta decay would be expected in the ten years that nEXO is expected to run.

Particle physicist Ben Jones of the University of Texas at Arlington — one of the leaders of the NEXT (Neutrino Experiment with Xenon TPC) collaboration – which searches for neutrinoless double beta decay using high pressure xenon gas, describes the nEXO team’s ability to detect barium atoms as “a very substantial advance”. He adds, “So far every experiment to detect this decay has been limited by backgrounds from other radioactivity. The detection of single barium ions could reduce backgrounds to a negligible level, which would be really paradigm shifting for the field.” However, Jones cautions that there is still much more work to be done before the technique is viable.

The research is described in Nature.

New superionic ice phase could shed more light on icy giant cores

By using shock waves to simultaneously compress and heat water to pressures of up to 400 gigapascals and temperatures of 3000 kelvin, researchers at the Lawrence Livermore National Laboratory in California and the University of Rochester in New York say they have produced a new phase of solid superionic ice. The ice XVIII, as it has been named, is made up of liquid-like hydrogen ions (protons) diffusing through a solid lattice of oxygen atoms. Such superionic ice is thought to form a large fraction of the interiors of the planets Uranus and Neptune and the new work could help us better understand the structure of these icy giants and perhaps even shed more light on their complex magnetic fields.

American physicist Percy Bridgman was the first to discover five solid water phases in 1912 and we now know of more than 17 crystalline and several amorphous ice structures. This unique behaviour of water partly comes from its weak intermolecular hydrogen bonds.

The LLNL team of scientists documented for the first time the existence of a solid lattice of oxygens with a face-centered-cubic (fcc) structure in superionic water ice. Credits: Millot, Coppari, Hamel (LLNL) – Picture by J. Russell. (From Left to right; Sebastien Hamel, Marius Millot, Federica Coppari)

“Our research aims to explore the unusual properties of water under extreme pressures and temperatures (like those that exist deep inside planets),” explains Marius Millot, who is the co-lead author of this new study. “Unlike the various phases of water we are familiar with (liquid, vapour and ice), we were able to create and study a new exotic ice phase called superionic ice.”

Superionic ice is predicted to exist when water is subjected to more than 100 gigapascal pressures and temperatures of above 2000 K. Here, the protons diffusing through the empty sites of the oxygen solid lattice allow the ionic conductivity of water to exceed 100 Siemens per centimetre, which is almost as high as the conductivity of metals. When ice is superionic, its melting temperature increases to several thousand kelvin and new ice structures with a close-packed oxygen lattice form.

Laser-driven shock waves

Creating such high pressures and temperatures in the lab is obviously very difficult, but Millot and colleagues have now used a series of laser-driven shock waves to do this. The researchers begin by first filling small cavities created between two thin diamond disks with a tiny droplet of water (30 μm thick and 1.5 mm across). They then place this droplet in vacuum at the centre of the Omega Laser target chamber at University of Rochester’s Laboratory for Laser Energetics and use six high-power lasers to generate a series of shock waves that squeeze and heat up the droplet.

“We very carefully designed this series of shock waves so that we could access pressures of 100 to 400 GPa (1 to 4 Mbar) at temperatures of 2000-3000 K,” says Millot. “Under these conditions, water is expected to become solid and crystallize into a dense ice.”

To test this hypothesis, the researchers performed X-ray diffraction measurements on the sample just a few billionths of a second after they had the launched the shock waves. They made these measurements using a group of 16 additional high-power laser beams to deliver 8 kilojoules of light in a one-nanosecond burst onto a 250-μm spot on a 2-mm²piece of a thin foil of iron that they placed 2 cm away from the water droplet.

Backing up previous research

“Under such intense radiation, most of the thin foil vaporizes and ionizes into a hot plasma that starts to emit X-ray photons at a very specific energy (its line emission),” explains Millot. “This flash of X-rays floods the water sample and since it has just crystallized into tiny nanometre-sized ice cubes, some of these X-rays are diffracted (deflected in particular directions, characteristic of the crystal structure adopted by the ice) and hit our image plate detectors.”

The technique allowed the researchers to confirm that the atoms are arranged in a regular lattice and that they had indeed solidified liquid water into a crystalline oxygen lattice of superionic water ice – on the timescale of just 3-5 nanoseconds.

The new result backs up previous research the researchers reported last year in Nature Physics, in which they obtained the first experimental evidence for superionic water ice at pressure-temperature conditions similar to those in the present experiments.

Slow convection

“As mentioned, these conditions are the same as those deep in the interior of Uranus and Neptune,” explains Millot. “Now that we have a clear and direct signature for a crystalline lattice in superionic water ice, we argue that this ice should not flow like a fast swirling liquid, such as the fluid iron outer core of the Earth, but that it should flow instead like the Earth’s mantle, which is made up of solid rocks yet convects on geological timescales.”

Our observation could help us better understand the internal structure of the icy giants, and indeed their water-rich exoplanet cousins, he tells Physics World. It could even shed more light on the complex magnetic fields on these planets. According to measurements made by NASA’s Voyager 2, these are thought to be quite different from the simple dipolar fields on Earth and other planets.

BCC to FCC

The X-ray diffraction data also allows the team to measure how the water ice compresses under these extreme conditions.

The laser compression experiment: — Artistic rendering of the laser compression experiment. Credits: Millot, Coppari, Hamel (LLNL) – Image by L. Krauss(LLNL)

“We did our experiments over a broad pressure range of between 1 and 4 Mbar and measured how compressible water is at these pressures,” says Millot. “It turns out that the observed behaviour agrees with theoretical predictions, but when we increase the pressure above 250 GPa near 2000 K, we find that ice undergoes a change in its atomic structure to adopt a more compact arrangement of the oxygen atoms.

“In fact, it goes from being a body-centred-cubic ice phase (probably ice X) to a novel face-centred-cubic superionic ice phase. Put simply, it goes from being a Rubik-cube-like lattice with oxygen ions at each corner of the cubes and one atom at the centre of each cube to one in which the oxygens occupy all the corners and the centre of each face of the cubes.”

Towards ice XIX

This is the first time that such a crystal structure has been observed for ice, so the researchers have dubbed it ice XVIII. Since this new phase is predicted to exist only at the high temperatures at which ice should become superionic, the result is further proof that water ice indeed becomes superionic under these conditions, says Millot.

Water isn’t the only molecule that could be studied using the technique described in this work, he adds. “We will now be able to study the thermodynamics and kinetics of crystallisation into new dense ice phases in similar molecular fluids. This is exciting because many materials have been predicted to have exotic new bonding states at extreme pressures and temperatures and we could now investigate these states.”

The team, reporting its results in Nature 10.1038/s41586-019-1114-6, says that it is now searching for ice XIX.

Coupled practices

Anna Demming ballet stretch — Common ground: *Physics and Dance* will appeal to more than just the minority of people who are trained in both physics and dance (such as Anna Demming, pictured, who is not only the materials editor of *Physics World*, but also a trained ballet dancer and co-founder of the South West Dance Theatre company). (Courtesy: Chris Hughes)

“It was a shame the discussion was so focused on the extremes,” was a recurring comment among people who attended a recent panel discussion on interdisciplinary science that I went to. Many of the delegates were working at the interfaces between physics, chemistry and maths. While these fields operate in distinct cultural and linguistic landscapes, the disciplines are not separated by the kind of gulf that exists between physics and biology, which were the fields straddled by the panellists. These comments made me smile because I happened to be reading Physics and Dance by Emily Coates and Sarah Demers at the time. If the gap seems so huge between physics and biology, then physics and dance must be operating on different planets entirely.

Despite the apparent divide, Physics and Dance is not the only book seeking to explore common ground between these two disciplines. As an example, Coates and Demers cite Kenneth Laws’ Physics and the Art of Dance, where the author eloquently describes the Newtonian mechanics at play in classical ballet. One characteristic that sets Physics and Dance apart is the breadth drawn on in the two disciplines, which not only includes the rudiments of mechanics and ballet, but also taps into the exotic irregularities of Einstein’s relativity and various more avant-garde movements in dance where fundamentally new philosophies are still emerging.

The result is neither a plodding account of conventional crossovers between physics and dance, nor is it a flight of fancy forcing dicey parallels of the most esoteric elements between the two fields. Instead, the book explores the evolution of dance, past and present, within a context of ideas that have developed in physics up to the current day; such that the reader is presented with a story that is still unfolding.

I found Physics and Dance a fascinating read. It handles both disciplines in a refreshingly egalitarian way that doesn’t just position them as commanding equal respect, although there is a sense of this too. For example, in the discussion of momentum, the authors describe it as something that “influences everyone but few people know how to wield the effects as virtuosically as dancers and physicists”. However, Coates and Demers take this equality further by demanding equal engagement from their readers with both disciplines. They allow equations to infiltrate explanations in a way that many pop-sci authors shy away from – indeed, they even provide physics problems for readers to enjoy playing with the ideas just described. Similarly, there are movement exercises that allow readers – from all levels of dance experience – to “feel” physics in action from the perspective of a dancer. And lest you kid yourself into reading these as mere “thought experiments”, Coates and Demers introduce these exercises with the instruction “put this book down”.

What emerges are ideas that don’t hop from the paradigms of one discipline to the other but share these paradigms at a fundamental level like the DNA of a newly fused zygote; and the potential outcomes feel exciting. I got goose bumps from the comment “It’s time to bring trigonometry to dance”, but what really got me hooked wasn’t simply reading how physics determines how dance movements work. Instead, by paying close attention to a YouTube clip, remembering your A-level physics and applying a bit of thought, you can reach a lot of those conclusions without the unique combined expertise of the two authors. Demers is a particle physicist working on experiments at CERN, while Coates is a dancer whose career has included work with choreographers such as Jerome Robbins, Mark Morris and Erick Hawkins, and performing alongside New York City Ballet and the likes of Mikhail Baryshnikov.

What really fascinated me in this book is reading about the role of cultural forces, akin to mechanical forces, in dance evolution; or how dancers have subconsciously drawn on both dance and physics aesthetics to develop movements, like George Balanchine’s form for a pirouette. For this, Coates and Demers take us to the studio where this form was born to witness the moment of creation as choreographer Balanchine presses soloist Suzanne Farrell to adjust the technique she has grown up with further and further until she is convinced she is being set up to fail. Instead, Farrell pulls off “the most glorious pirouette she had ever felt”, thanks to Balanchine’s masterful handling of torque.

While Coates and Demers do include other physics topics, a lot of the book is devoted to mechanics, taking readers steadily through the basics. Parts of this discussion could be a bit of a yawn for people already familiar with these ideas. Readers with a background in physics might therefore be tempted to skim some of these sections, and there may be parts that don’t do a lot for anyone – the discussion of units will be old news to the initiated, and won’t be relevant or enthralling for those new to the idea. However, I would argue that most of the book retains appeal for all. The language is rich: air doesn’t just occupy the region directly above sea level, but “hugs the Earth” as a result of the same gravitational force that stops us flying off the planet. Twyla Tharp is not just a choreographer but an “alchemist of motion”.

Physics and Dance is essential reading for those with an avid passion for both topics. It should also appeal to the many dance professionals who have a fruitful muse in science. After all, the idea that the human body should play a role in the physicist’s search for fundamental laws has been bandied about for centuries – optics pioneer John Tyndall is just one example. As Coates and Demers put it: “People feel sensorial engagement with friction that boxes don’t,” adding that, at the same time, “In dance, friction produces meaning.” Reading Physics and Dance is an insightful reminder that the two disciplines have developed on the same planet after all, and that exchanging ideas that encompass them both is definitely worth the effort.

2019 Yale University Press 192pp £22.50hb

Targeting cancer with gold nanoparticles is just the start…

Researchers in the US have explored the impact of specific proteases expressed by cancer cells on biomolecules that form around gold nanoparticles targeted at pancreatic tumours. They found that the effect of proteases on the aggregated biomolecules is complex (ACS Appl. Mater. Interfaces 10.1021/acsami.9b00928).

Gold nanoparticles show promise as potent drug carriers for cancer treatment and diagnosis. However, the engineering of gold nanoparticles is just at its beginning. Notably, their interaction with biomolecules found in biological fluids during therapy is a major topic of investigation. These biomolecules, which occur in different compositions, spontaneously form a “cloud” around the gold nanoparticles, referred to as a “protein corona”.

Protein corona composition has become a major factor in customizing gold nanoparticles for drug delivery. But despite all the studies performed to date, the impact of protein corona composition on the interaction between gold nanoparticles and cancer cells that secrete matrix metalloproteinases (MMPs) remains relatively unexplored.

MMPs are a group of enzymes that degrade different proteins, especially collagen. MMPs help cancer cells proliferate and migrate faster throughout healthy tissue by degrading the extracellular matrix and therefore creating free space for cancer cells to spread. It is known that various compositions of the protein corona may affect this degradation process. But since MMPs are proteins themselves, their exchange with other proteins in the corona potentially gives rise to a complex net effect.

Protein selection

To investigate the impact of proteases, the researchers — led by Kimberly Hamad-Schifferli at the University of Massachusetts Boston — studied coronas composed of different model proteins. They used two main criteria to choose the different model proteins: the strength of their interaction with gold nanoparticles, and the proteases that pancreatic cancer cells secrete. The team used an established pancreatic adenocarcinoma cell line called PANC-1, which secretes two major MMPs: MMP-2 and MMP-9. In this work, they focused more on studying MMP-9.

In order to work with a well-studied system, the researchers chose human serum, as it offers both strongly- and weakly-bound corona proteins. They also used pure human serum albumin as a model that involved only weakly-bound corona proteins when inside a biological fluid.

To more specifically study MMP-9 activity, the researchers chose collagen IV as another corona protein, as it is the substrate of MMP-9. Then to search for the specific proteins that are degraded by the proteases that PANC-1 cells secrete, and to probe the protein corona composition, they introduced a protease inhibitor to the cell medium. Finally, they isolated corona proteins from the gold nanoparticles inside the cell medium and analysed these via mass spectrometry.

Protein corona degradation

Focusing on MMP-9, the team found that its activity influenced the final composition of the protein corona in cell medium, as well as its properties, such as the time scales for exchange, adsorption or degradation. In particular, the researchers found that size of the corona changes. However, the factors resulting in either an increase or decrease in the size of protein corona could not be analysed — the changes are not straightforward. Exposure to MMP-9 does not always lead to a decrease in the size of protein corona due to digestion; as MMP-9 itself is a protein, it can exchange with the gold nanoparticles in the fluid. As a consequence, this varies the size of the protein corona depending upon the MMP-9 on/off binding states.

“Together, these results indicate that the mechanism of protease activity on gold nanoparticles coronas involves both rearrangement and exchange, followed by degradation,” the authors concluded.

Expanding US cropland emits same as 36 new power plants

Between 2008 and 2012 expansion of cropland in the US released carbon each year equivalent to the running of 36 coal-fired power plants, according to scientists in the US.

“Folks can easily see and understand how tropical deforestation removes carbon from the landscape and emits it to the atmosphere as carbon dioxide,” says Seth Spawn of the University of Wisconsin–Madison, US. “But in the US and other more temperate areas, land-use change disproportionately affects grassland ecosystems where – being stored underground – the vulnerable carbon is far less visible, but nevertheless abundant.”

The total emissions from this uprooting of millions of hectares of grassland were roughly the same as those from deforestation of the Cerrado, Brazil’s vast tropical savannah, the scientists say.

“We tend to neglect what we can’t see,” adds Spawn.

In the past, carbon stored in grassland has also been hidden from scientific instrumentation. But recently, improved US maps of soil properties have enabled scientists like Spawn and colleagues to know where the carbon lies, and how it is affected by land-use change.

The researchers overlaid these maps with new, high-resolution maps showing the precise locations of nearly seven million acres of farmland that were first cultivated between 2008 and 2012. Then they used statistical models to estimate how much of the carbon at those sites was released to the atmosphere during cultivation.

The total emitted was more than 38 million tonnes of carbon a year for 2008–2012. Depending on the region, that’s up to 14 times greater than estimates made by the official US greenhouse gas inventory – a discrepancy that warrants further study. “It suggests the US government could potentially be under-reporting emissions from land-use change,” says Spawn.

Spawn believes that emissions like these could be avoided via land retirement and preservation programmes, if enrolment criteria were expanded to include the carbon buried in grassland. A study by a large US team last year concluded that avoiding emissions from land-use change and mismanagement alone would allow the US to meet its obligations to the Paris Agreement.

Spawn also points out an irony of the land-use change – much of it could have been motivated by meeting the US mandate for biofuel, which is supposed to reduce greenhouse-gas emissions. For that reason, he and his colleagues are working with economists to see how biofuel policy could be driving emissions.

In addition, the researchers are integrating their emissions model into life-cycle assessments, to understand how emissions from land-use change are linked to those from products derived from crops.

“In recent years, we’ve seen relatively high rates of cropland expansion in the US,” says Spawn. “While the tendency is to ignore the potential carbon implications of these changes because the carbon isn’t standing there in the open, our study suggests that these are not changes to be taken lightly.”

Quantum nanoconfinement effects observed without confinement

The means for exploiting quantum effects in the electronic behaviour of nanoscale materials has been an attractive attribute for next generation devices that is unique to nanomaterials – or is it? Researchers in Madrid, Spain, have now observed the quantization of electron energy levels in copper similar to the effects of confinement within a nanostructure, but in a copper sample with no nanoscale dimensions in the plane of the observed effects.

Roberto Otero and colleagues at Madrileño de Estudios Avanzados en Nanociencia (IMDEA-NANO), Instituto de Ciencia de Materiales de Madrid (ICMM-CSIC) and Universidad Autónoma de Madrid studied the electronic characteristics of the electrons forming a two-dimensional electron gas (2DEG) at the surface of a copper sample with the organic material tetracyanoquinodimethane (TCNQ) deposited on it. For their experiments they use low-temperature scanning tunnelling microscopy and spectroscopy, whereby an atomically sharp tip close to the surface with a potential difference between the tip and surface allows electrons with enough energy to “tunnel” through the insulating barrier to the tip and yield a current. This way Otero and team could map the energy and density of states of the electrons.

The TCNQ deposited self-assembles into regular nanoscale island structures that form an edge with one-dimensional periodicity on the copper. To observe conventional quantum confinement effects requires two edges so that the copper 2DEG is confined within the two, however, the researchers observed a two-dimensional array of maxima and minima electron energies like a 2D standing-wave pattern in the 2DEG with just one edge of TCNQ islands. They attribute the effect to Bragg diffraction – the same effect that gives CDs their iridescent colour – as waves of arriving electrons interfere with those reflected from the edge.

“To our knowledge, this is the first example in which the discretization of the electronic structure around solid-state nanostructures is not caused by electron confinement but by diffraction,” report the researchers in Physical Review Letters. Although other examples of wave-like electron behaviour exist, this kind of Bragg diffraction has eluded experimental observation altogether so far.

Edge matters

The researchers compared their results with the electron characteristics on bare copper and at a step edge in the copper as opposed to the edge of the TCNQ island structure. As expected they found that the conductivity oscillated with distance from the edge or scattering defect on the bare surface, with the period of the oscillations increasing with distance just as the distance between ripples from a stone dropped in a pond increase with distance. However, at the TCNQ edge they found additional contributions to the pattern of oscillations.

To understand their results the researchers examined transfer of momentum of the electron wave within the context of the laws of crystallography that govern incoming and outgoing waves as set out by Max von Laue, and which reduce to Bragg’s Law. In particular they examined the change in momentum parallel to the edge, where the superposition of scattered waves incident from different directions should give standing waves with different periodicities that blur out, but instead they found the electronic behaviour dominated by electrons with energy at specific quantized levels separated by the reciprocal of the periodicity of the edge of nanoislands. They suggest that the same effect is present at the copper step edge but since the spacing of the energy levels corresponds to the inverse of the spacing of the copper atoms, it is too large to observe.

They conclude in their report: “Since these energies are in turn determined by the periodicity of the scatterers, we conclude that Bragg-diffraction discretization offers a new avenue to tailor the DOS [density of states] at the Fermi level, and thus the physical properties of materials, from the superconducting transition temperature to their thermal stability.”

Full details are reported in Physics Review Letters.

Clinical trial explores BBB opening in fight against Alzheimer’s

A new clinical trial is investigating the potential of blood–brain barrier (BBB) opening as an innovative procedure in the fight against Alzheimer’s disease. The trial, being run at Ohio State University Wexner Medical Center, Weill Cornell Medicine and WVU Rockefeller Neuroscience Institute, is using non-invasive low-intensity focused ultrasound to open the BBB in patients with Alzheimer’s.

“While it’s protective and beneficial for day-to-day brain function, when we think about therapeutics, the blood–brain barrier poses a significant challenge,” says Vibhor Krishna, a neurosurgeon at Wexner Medical Center. “The focused ultrasound procedure allows us to non-invasively access the brain tissue so treatment can be administered straight to the site of pathology.”

The procedure takes place in an intraoperative MRI-surgical suite, where MR imaging guidance allows doctors to target a specific area of the brain where there is a build-up of toxic amyloid proteins, which are associated with the onset and progression of Alzheimer’s disease.

The patient’s head is immobilized in a head frame during the treatment. The ultrasound transducer elements are contained within a helmet-like device that is attached to the head frame. Surrounding the patient’s head is a water bath circulating cold, degassed water. This setup helps transmit some 1000 focused ultrasound beams through the intact skull to focus at the exact region of brain tissue that is being targeted.

During the procedure, the patient’s bloodstream is infused with microbubbles. The focused ultrasound causes these microbubbles to expand and contract, which mechanically opens the BBB. The patient is awake and alert throughout, giving real-time feedback to the treatment team. The hope is that that simply opening this barrier may help clear amyloid from the brain.

“In this research study, we are not delivering any medications,” Krishna explains. “Our hypothesis is that, by opening the blood–brain barrier, a patient’s own immune defence may clear some of those harmful amyloids. If we determine this to be safe, in the next steps we would want to understand the effectiveness and the impact of opening the blood–brain barrier in improving cognitive decline.”

The procedure is performed three times at two-week intervals to allow for as much amyloid clearance as possible. The research team will monitor the patients closely, using neurological exams and neuro-psychological exams to assess language, memory and executive functioning at various intervals for one year following the surgery. In the future, this method of opening the blood–brain barrier may also be applicable in developing new treatments for brain tumours and epilepsy.

The clinical trial, sponsored by Insightec, will enrol up to 10 patients.

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