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From actinium to zinc

To mark 2019 being the International Year of the Periodic Table, members of the Physics World team have been having some chemical “fun” in our self-styled Battle of the Elements. It involved staff picking their favourite element and arguing the case in a series of blog posts and podcasts (check out the Physics World Weekly podcast of 11 July). I picked uranium because it was the element that led to the discovery of three crucial physics phenomena: radioactivity, isotopes and fission. And as I was reminded when reading Elementary: the Periodic Table Explained by James M Russell, uranium is also responsible for much of the heat inside planets.

Timed to coincide with the 150th anniversary of Dmitri Mendeleev’s creation of the periodic table, the book offers readers a potted account of all 118 known elements, from old favourites such as silicon and iron to rarer stuff like tellurium (vital for solar panels) and ruthenium (found on the nibs of the famous Parker 51 fountain pen no less). That’s a lot of elements to get through, and Russell – a science writer – has had to be selective, with most getting just two pages apiece. Neatly packaged with a pretty chequerboard cover, the book will be perfect for friends and family members who aren’t scientists and simply want a short, sweet overview of each element, from actinium to zinc.

Carbon, the winner of the Physics World Battle of the Elements, naturally gets its place too. It’s vital for life and has a clear physics angle through diamonds and graphene – that wonder material first properly isolated by physicists in 2004. However, I was disappointed that elements heavier than uranium, which don’t occur naturally, get barely a paragraph each. That seems an injustice for physicists, who’ve led the way in creating these fleeting entities in nuclear-physics labs around the world. Also given scant treatment are the “lanthanides” – those misfits that sit in two rows stuck below the main part of the periodic table. Indeed, Russell doesn’t really “explain” why they’re placed there at all. But then maybe there is no explanation – after all, to physicists, surely the periodic table is nothing more than a way of putting the elements in some sort of order? As Ernest Rutherford, the physicist who won the 1908 Nobel Prize for Chemistry, famously sniffed: “All science is either physics or stamp-collecting.”

2019 Michael O’Mara Books 186pp £9.99hb

Autofocal glasses automatically adapt to viewing distance

Do you know that as you get older, the flexible crystalline lenses in your eyes become stiffer? This stiffness makes it difficult for the lens to deform its shape to suit the distance you are aiming to look at. This reduction in the range of accommodation of the eye’s lens is known as presbyopia and affects more than a billion people, particularly the elderly population.

Recent technology advances have provided different solutions to correct presbyopia by offering several types of glasses and contact lenses. Yet, these forms of correction all have shortcomings. For instance, “progressives” (which split far and near focus vertically in each lens) perform poorly in tasks requiring side-to-side head movement as they cannot adjust for the changes in focus during such movements. Others, like “monovision” lenses (which split far and near focus between the two eyes), fall short on visual acuity and near-distance performance.

Smart glasses focus automatically

The main reason for these methods’ flaws is that they all employ fixed focal elements and therefore can only achieve an approximate adjustment for vision correction. Approaching a more natural remedy, such as attaching a flexible lens to the eye’s ciliary muscles, would require invasive surgical procedures to restore the flexibility of the crystalline lens or implement some form of focus-tunable lens element.

To overcome these shortcomings and achieve the optimal adjustment to the correction lens, a research team – led by Gordon Wetzstein at Stanford University – designed focus-tunable eyeglasses called autofocals. The researchers used two infrared-sensitive cameras to determine the relative angle between the eyes – known as vergence. This angle is directly related to the depth at which the viewer is focusing (Science Advances 10.1126/sciadv. aav6187).

The authors (from left to right): Gordon Wetzstein, Nitish Padmanaban and Robert Konrad.

In other words, one camera records the location of everything in the outside world and the other camera faces the eyes to track where they are looking. Based on information regarding the location of binocular disparity (the difference in an object’s location seen by the right and left eyes) and the horizontal distance between objects in the images, the autofocals combine the images from the two cameras and enable the user to calculate the distance of the object that the viewer is looking at.

Adjusting the lens to object depth

The research team built a wearable prototype that combines electronically controlled liquid lenses enclosed in glass and metal with two chambers separated by a membrane, a wide field-of-view depth camera and binocular eye tracking. The flexibility of the membrane is achieved by pushing the liquid lens into or out of the two chambers.

The team compared their autofocal design against progressive and monovision lenses using metrics including visual acuity (sharpness), contrast sensitivity and refocusing rate. They found, for instance, that their design helped people to maintain 20/20 visual acuity at tested distances of 0.167, 1.25 and 2.5 D (dioptres, equal to the reciprocal of focal length in meters). In order to account for near- and far-sight correction or astigmatism, the team used an offset lens to test a wide variety of conditions in a wide variety of people.

The researchers concluded that focus-tunable eyeglasses perform better than (or at least comparable to) progressives and monovisions in terms of visual acuity and contrast sensitivity, and enable faster and more accurate adjustments in focus.

“Despite power requirements and remaining engineering challenges, our study demonstrates that a paradigm shift toward digital eyeglasses is valuable, with the benefits extending beyond presbyopia correction. What seems at first like a disadvantage, the need for a battery, actually opens the door to more capabilities,” the authors wrote.

Can surface treatments enable commercial perovskite solar cells?

Lower costs, shorter pay back times and even higher efficiencies than pure silicon – the promise of perovskites for solar cells may sound too good to be true, and so far it has been. Perovskites are unstable under heat, oxygen, moisture, electric fields and light irradiation – a catalogue of sensitivities that are quite catastrophic for solar cells that need to be exposed to the weather to harness sunlight into electricity.

Unsurprisingly a vast number of groups around the world are avidly researching ways to improve the resilience of perovskites. These efforts include two recent papers in Science reporting different types of surface treatments that go some way to help stabilize perovskites under exposure to sunlight.

Oxysalt passivation

Jinsong Huang alongside Shuang Yang and Shangshang Chen at the University of North Carolina at Chapel Hill and University of Nebraska–Lincoln in the US, and colleagues in the US and Italy, focused their attention on organic-inorganic hybrid lead halide perovskites, including CsFAMA and MAPbI₃, where FA is formamidinium and MA is methylammonium.

“This was not an experiment by design,” Huang tells Physics World, as he describes how they had initially thought about using sulfate ions to passivate the defects that both inhibit the power conversion efficiency and foster degradation. “However we found some interesting phenomenon during this study which shows these “passivation ions” to be different from many other passivation molecules we have been studying in the last five years.” They had discovered that these ions react with perovskites forming a white product that remains insoluble in many solvents. By unravelling the reactions and mechanisms behind the product formed they demonstrated its effective use as a capping layer.

The lead oxysalt layer they formed binds strongly to the perovskite surface and protects it from the detrimental effects of stimuli in ambient atmosphere and light conditions. Following extensive studies of device performance and the activation energy at the surfaces of the perovskites, Huang and colleagues conclude that the strong bonds immobilize surface defects such as vacancies, suppressing ion migration. As a result, the efficiency of the solar cell increased to 21.1% for CsFAMA perovskite compared with 19.16% for the control, and it maintained 96.8% of the initial efficiency after operation at maximum power under simulated air mass (AM) 1.5 G irradiation for 1200 hours at 65°C. In contrast the efficiency of the control device plummeted from 18.2% to 8.54% after testing for just 474 hours.

Going organic for inorganic perovskites

A collaboration of researchers in China, Switzerland and Japan focused their efforts on CsPbI₃. Yixin Zhao at Shanghai Jiao Tong University, Ibrahim Dar and Michael Grätzel at Ecole Polytechnique Federale de Lausanne (EPFL) in Switzerland and Yabing Qi at Okinawa Institute of Science and Technology Graduate University in Japan led the project.

The search for silicon’s successor

At around 15%, the power conversion efficiency of inorganic lead perovskites is lower than their inorganic-organic hybrid counterparts, primarily because of the larger bandgaps. While the bandgap of CsPbI₃ is more promising, its instability isn’t. However Zhao, Grätzel, Qi and Dar, and their co-workers were able to grow stable CsPbI₃ with a crystal microstructure described as β- CsPbI₃through a facile solution chemistry deposition. They then coated the perovskite in choline iodide (CHI) and here the fact that CsPbI₃ is purely inorganic has advantages.

“The CHI can penetrate through the CsPbI₃ film because the CHI would not react with CsPbI₃ but may react with hybrid perovskite,” explains Zhao. “Furthermore, the CHI would not only passivate the defects but also modify the band alignment in the device.” The net result was perovskite solar cells with highly reproducible and stable efficiencies reaching 18.4% at 45 ± 5°C under ambient conditions.

Closer to commercial stability?

“The perovskite solar cells wrapped by the oxysalts are much more stable than what we had in the past,” says Huang, although he highlights the further work needed, such as longer testing. Their testing period was limited to two months and use of acceleration tests present further issues because the industrial standard of acceleration tests are all for silicon solar cells. “There is no standard for perovskite solar cells yet so it is still hard to compare, but we know for sure the perovskite solar cells are still far behind silicon solar cells in terms of stability.”

Commenting on the work, Martin Green – Scientia Professor at the University of New South Wales, Sydney, and Director of the Australian Centre for Advanced Photovoltaics, who was not involved in these latest developments but has over 40 years’ experience in solar cell research – says, “the paper does, as the authors state, report a perovskite device that is “one of the most stable reported”.” However, he added that the figures Huang and colleagues cite correspond to about 8 months illumination in the field, suggesting more than 4% degradation per year from light exposure alone.

How have solar cells undercut coal?

Green highlights the specifications of present module warranties, which are generally less than 2-3% degradation in the first year, then less than (0.5-0.7)% per year in the 25-30 subsequent years, for degradation from all causes, and adds “Even this device, one of the best perovskite results so far reported, falls far below the stability expected from a commercial product, when tested in isolation under just one of the stresses cells will see in the field. These perovskites are expected to be much more sensitive than silicon to all the other stresses.”

As for the CHI-passivated inorganic perovskite solar cells, the efficiency improvements are impressive, and the technique points towards progress on the stability front too. However, while the devices maintained 95% power conversion efficiency over 240 hours continuous illumination, this falls still further behind the rates of degradation that commercial solar cell providers can afford than the oxysalt encapsulated cells.

Zhao also comments on possible issues around the lead content found in both the solar cells reported. “The toxicity of lead would be an issue for large-scale application but It can be solved by some control just like the lead acid battery. Of course, we should also try to develop some low-lead or even lead-free perovskite for photovoltaics in future.”

Outlook

Despite the achievements their reports proclaim, the researchers behind both papers are quick to highlight the outstanding challenges. Zhao suggests that future work will push to increase efficiencies of their inorganic perovskite solar cells further still. As for Huang, he points to a clear need for further enhancing the stability of their cells without compromising the efficiency, adding. “More importantly, we need to transfer the lab-scale process to an industrial-scale manufacturing process.”

Full details of the inorganic-oxysalt-passivated solar cells and the CHI-passivated inorganic CsPbI₃ solar cells are published in Science.

Active matter goes chaotic

Topological defects in the structure of materials known as active nematics can act as rods that mix the fluids – much like one might mix colours in white paint. This is the new finding from researchers at the University of California, Merced, who say that the mixing is a result of sliding on a molecular scale. The work, which has applied chaotic advection to the emerging field of active matter for the first time, could help advance our fundamental understanding of how defects move collectively in liquid crystals.

Nature abounds with examples of active matter, with some well-known examples being flocks of birds, fish and insects, sheets of biological cells and swarms of bacteria. Researchers have been trying to make biomimetic and synthetic active materials in the laboratory from materials such as self-propelled colloids and dense phases of mechanically driven biopolymers. Needless to say, they would like to better understand the fundamental physics of these systems.

“Intriguing” non-equilibrium systems

“Active matter is attracting a huge amount of research interest at the moment,” says co-team leader Linda Hirst.

“They are intriguing because they are non-equilibrium systems (which cannot be described in the framework of conventional thermodynamics) in which energy is injected on the microscale throughout the structure, ultimately giving rise to macroscopic coherent motion,” adds co-team leader Kevin Mitchell. This large-scale motion can produce emergent structures such as phase boundaries and topological defects, where local order breaks down.

In their work, Mitchell, Hirst and colleagues studied active nematic fluids, which are a new class of soft materials that can be formed from anisotropic molecules such as biological filaments (as in this work). The fluid they investigated comprises two basic components, both found in biological cells: microtubules and kinesin motors. Microtubules are filaments of long, semi-flexible protein assemblies and the researchers could see bundles of these filaments sliding past each other in microscopy images. Kinesin is a protein that can convert chemical energy, in the form of ATP, to mechanical energy.

“The kinesin molecule has two binding sites (or ‘feet’) that bind and unbind to a microtubule one after the other, to produce a ‘walking’ motion along the microtubule,” explains Hirst. “In our fluid, pairs of motors are connected back-to-back so that the feet of the two motors walk on two different microtubules.”

Kevin Mitchell. Courtesy: University of California, Merced

Large-scale advection

This process produces a shearing motion between the neighbouring microtubules that causes the filaments to extend past each other, effectively stretching the fluid locally in the direction of the microtubule, she adds. As the material stretches, topological defects spontaneously appear and cancel each other out, generating large-scale advection in the fluid. “This material was originally invented by Prof. Zvonimir Dogic when he was at Brandeis, and who is now at UC Santa Barbara.

“There aren’t many examples of active nematics that we can use in the lab,” she says. “We wanted a small-scale system in which we could observe fluid behaviour but one that was large enough to allow us to observe individual elements (with fluorescence microscopy, for example). We chose to work with the microtubule/kinesin system because it is the only example to date of a molecular-level extensile active nematic that can remain in a steady state for long periods.

“The fact that we were able to collaborate with the material’s inventor and receive materials from the Brandeis biomaterials facility was also an important factor for us when making our choice.”

The Lyapunov exponent and topological entropy

The researchers studied the self-driven advection and mixing on different length scales in their system using two techniques. They measured stretching on the local scale by the Lyapunov exponent and more large-scale mixing by analysing the way in which the topological defects move around one another.

“The Lyapunov exponent is a quantity employed in chaos theory,” explains Mitchell. “It describes how quickly two points in the fluid move away from one another and is thus very closely related to the extensile, or stretching, nature of the material.”

In this image, the stretching nematic contour line traced by two separating topological defects is shown. Courtesy: Linda Hirst

The researchers say they measured the Lyapunov exponent using the velocity-gradient at every point in their system.

For larger scale measurements, they used the analogy between the motion of the defects and patterns of braided strings. They did this by adapting ideas from braid theory in mathematics to compute the amount of stretching in the fluid (or the topological entropy) caused by the motion of the defects. “Quantitatively, we found that the topological entropy and the Lyapunov exponent were quite close to one another, with the former being slightly larger than the latter,” Mitchell tells Physics World. “We were quite pleased with this agreement since theory predicts that the topological entropy is an upper bound to the Lyapunov exponent in systems like ours.”

Studying the effects of confinement

The researchers say they are “excited” about bringing together the two disciplines of active nematics and chaotic advection and believe that studies like theirs will continue to provide new insights into both fields.

They will now be focusing on studying the effect of confinement on chaotic mixing in their active nematic. “For example, what happens when the material is confined to wells of different geometries or to channels?” asks Hirst. “Can we control the topological entropy by tuning either the confining geometry or by other external factors?”

“We are also interested in studying the fractal patterns displayed by our system and what their physical origins might be,” adds Mitchell.

Full details of the research are reported in Nature Physics 10.1038/s41567-019-0600-y.

Water bears on the Moon, tricky maths problem, and an atomic tipple

The Moon could now be home to thousands of tardigrades – creatures under a millimetre long that are known to survive incredibly harsh conditions – thanks to an Israeli mission that crashed there in April. The creatures, also known as water bears, were flown to the Moon aboard the Beresheet lander, which was built by SpaceIL – a private company based in Israel. However, just minutes before landing, the firm lost contact with the craft and it crashed.

The 10,000 tardigrades had been dehydrated to place them in suspended animation and then encased in artificial amber in the craft’s payload. But Nova Spivack, the co-founder of Arch Mission Foundation that was involved with mission, notes that the creatures could have survived the crash and simply be re-animated by placing them in water. Given that they can survive being frozen to almost absolute zero, you wouldn’t bet against them.

The PEMDAS way

What is the answer to the following: 8÷2(2+2)? What at first might seem rather simple, is actually anything but. This equation was posted last week on Twitter and quickly went viral reaching 15,000 likes and causing countless headaches and arguments. The reason is that people generally reach two different answers: 16 or 1. Indeed, one user even uploaded an image showing two calculators with a different answer.

Steven Strogatz, a mathematician from Cornell University, writes in the New York Times how the solution depends on how you have been taught the rules governing the “order of operations”. Most are taught the PEMDAS way — parentheses, exponents, multiplication, division, addition, subtraction – in which case arriving at 16. But others are taught that “implicit” multiplication should be given higher priority than “explicit” multiplication or division, in which case the implicit multiplication 2(2+2) is given higher priority than the explicit division in 8÷2(2 + 2), resulting in 1. Many, however, have simply balked at the question itself saying that it is badly formulated. As Strogatz concludes: “If you want a clearer answer, ask a clearer question.”

Atomic tipple

Finally, would you try a vodka that is made with grain and water from the exclusion zone in Chernobyl? Well, now you can thanks to Atomik – an “artisan vodka” – that has been produced by the Chernobyl Spirit Company. Those behind the 40% ABV tipple say it is the first consumer product to come from the abandoned area around the damaged nuclear power plant.

Environmental scientist Jim Smith from the University of Portsmouth reassures would-be consumers that there is no danger of radioactivity from the spirit thanks to the distillation process. “This is no more radioactive than any other vodka,” he told BBC News adding that it has even been tested for radioactivity in a lab at the University of Southampton. “They couldn’t find anything – everything was below their limit of detection,” he says.

The team hope to use the profits to help communities in Ukraine still affected by the economic impact of the accident. So how can you get your hands on this unique beverage? Currently there is only one bottle available, but the team hope to produce 500 bottles by the end of the year selling it initially to the “nuclear tourists” who visit the exclusion zone.

Neuron-inspired electrical model goes quantum

An electrical circuit inspired by the functionality of a neuron can operate in the quantum regime, according to recent models by a team of scientists from Spain and China. The researchers found that the distinct dynamics of information transport through a neuron are preserved when the signal is fully quantized. This merging of brain-function inspired networks and quantum informatics could lead to enhanced computing systems, as well as benefit growing research fields such as quantum machine learning.

The idea that information travels through neurons like electrical signals through a circuit is known as the Hodgkin-Huxley model. This was awarded the 1963 Nobel Prize in Medicine and created a strong link between physics and neuroscience. Since then many attempts to improve efficiency and speed in computation have taken inspiration from neurons, mimicking architectures found in the brain. Now, a new study revisits the fundamental Hodgkin-Huxley model to investigate its operation in the quantum regime.

A circuit’s memory

The scientists, led by University of the Basque Country’s Mikel Sanz, considered the dynamics of the potassium ion channel through a neuron cell. The variable concentration of ions passing through the cell membrane within the Hodgkin-Huxley model is normally simulated by introducing a nonlinear conductance. To represent that, the scientists made use of the concept of a memristor.

A memristor has “memory” of the electrical signals that have passed through it and has resistance that depends on that history. Back in 2016 Sanz was involved in the first model of a quantum memristor. Using this model was key for the researchers’ quantized circuit version of Hodgkin-Huxley.

The team considered an alternating current source for the system dynamics in both the classical and quantum regimes. In the latter case, they modelled parts of the circuit as semi-infinite transmission lines in order to fully quantize the electric signals. These transmission lines would have inductors joined in series and capacitors in parallel.

Quantum nature emerges

The scientists’ simulations confirmed that the Hodgkin-Huxley model can indeed operate in the quantum regime while preserving the main features of its dynamics. Curiously, the team found that even when the circuit was quantized, the signal response was classical in nature. However, they found that the expression for the second moment of the voltage – which gives the average power output – had a term of fully quantum origin. According to the researchers, that term relates to the circuit’s zero-point energy – the lowest amount of energy that a quantum system may have.

In practice it is superconducting circuits at ultra-low temperatures that allow access to the quantum regime of electric signals. In 2017 Sanz took part in research on a realistic quantum memristor that could be integrated in such circuits. With the rate at which such technologies develop, this continued research could lead to functional quantum neuron-inspired networks. This offers an alternative route towards the realization of a universal quantum computer.

You can read the full article in Physics Review Applied.

MR/RT for precision radiation medicine: Celebrating one year of clinical activity with Elekta Unity

Animals adapt to climate heat, but too slowly

German scientists have an answer to the great question of species survival: can animals adapt to climate change? The answer, based on close analysis of 10,000 studies, is a simple one. They may be able to adapt, but not fast enough.

The question is a serious one. Earth is home to many millions of species that have evolved – and adapted or gone extinct – with successive dramatic shifts in climate over the last 500 million years.

The rapid heating of the planet in a climate emergency driven by profligate fossil fuel use threatens a measurable shift in climate conditions and is in any case coincident with what looks like the beginning of a mass extinction that could match any recorded in the rocks of the Permian, or other extinctions linked with global climate change.

The difference is that climate is now changing at a rate far faster than any previous episode. So can those animals that cannot migrate to cooler climates adjust to changing conditions?

A team from the Leibniz Institute for Zoo and Wildlife Research in Berlin and more than 60 colleagues from around the world report in the journal Nature Communications that they examined whether creatures could change either their physiology, size or behaviour to accommodate a rise in temperature accompanied by a change in the timing of the seasons. Biologists call this kind of response “phenotypic change.”

Questions like these are not easily answered. To be sure, the biologists needed reliable local records of temperatures across a number of locations. Then they needed sure information about the timing of migration, reproduction, hibernation and other big events in the lives of their subjects over a number of years.

And then they needed to find case studies where data had been collected over many generations in one population of creatures in one space.

And having found changes in the traits of their selected creatures, the biologists had to work out whether such changes led to higher levels of survival, or more offspring. They found reliable information about 17 species in 13 countries.

Pessimism alert

In the end, most of their data came from studies of birds, among them common and abundant species such as the great tit Parus major, the common magpie Pica pica or the European pied flycatcher Ficedula hypoleuca.

The message is that even if bird populations can change with their environmental conditions, they may not be able to do so at the speed necessary to time migrations to coincide with ever-earlier spring flowering, or nesting to match the explosion of insect populations that provide food for nestlings.

“Even populations undergoing adaptive change do so at a pace that does not guarantee their persistence,” said Alexandre Courtiol of the Leibniz Institute. And the data available apply to species that are known to cope relatively well with changing conditions.

“Adaptive responses among rare or endangered species remain to be analysed,” said his colleague and co-author Stephanie Kramer-Schadt, a Liebniz ecologist. “We fear that the forecasts of population persistence for such species of conservation concern will be even more pessimistic.”

This article first appeared at Climate News Network

MRI reveals molecular composition of the brain

Aviv Mezer and colleagues at the Hebrew University of Jerusalem have developed a mathematical model that compares the water content of the brain with measures of physical properties obtained from MRI scans to calculate the molecular composition of lipids in the brain. They say that this technique could detect changes in the biological makeup of the brain over time and identify key changes associated with diseases like Alzheimer’s (Nature Communications 10.1038/s41467-019-11319-1).

MRI scans are a non-invasive way for doctors to view a patient’s brain and check for disease-related changes. The information provided is limited, however, as it only provides images of the brain tissues with little information on their molecular composition.

“When we take a blood test, it shows us the exact number of white blood cells in our body and whether that number is higher than normal due to illness. MRI scans provide images of the brain but don’t show changes in the composition of the human brain, changes that could potentially differentiate normal aging from the beginnings of Alzheimer’s or Parkinson’s,” explains Shir Filo, a co-author on the latest research.

To address this, the team turned to a technique known as quantitative MRI (qMRI).

MRI scanners use powerful magnets to align the protons (hydrogen atoms) in water molecules. Radiofrequency waves then excite the protons, which as they relax, produce weak radiofrequency signals that the scanner can detect. Images are created based on the varying relaxation times between different tissue types. qMRI also measures and records physical properties such as relaxation time, magnetization transfer rate and the water fraction. This information has been shown to be linked to biophysical properties of brain tissue.

To see whether the composition of lipids in brain tissue could affect these physical parameters, and therefore be measured by them, Mezer and colleagues conducted MRI scans on model lipid mixtures containing common brain lipids. This revealed unique relaxation signatures for different lipids. Next, they validated their results with MRI measurements and post-mortem data on the lipid composition of different brain tissues from a previous study.

“We found that many qMRI physical parameters are very sensitive to the water fraction and also affected by the environment,” Mezer tells Physics World. “In the brain, MRI is primarily a measurement of water hydrogen. We found that after accounting for this dependency – of the qMRI parameters on water fraction – we can characterize the interaction between water and the biological environment. In particular, we showed that changes in abundance of molecules such as membrane lipids can be monitored in this way using MRI.”

The researchers believe that their MRI technique could provide crucial insight into how our brains age. To test this, they conducted MRI scans on 23 adults in their late 20s and 18 adults in their late 60s and early 70s. In agreement with previous theories, they discovered distinct ageing patterns in different brain regions. They were able to identify region-specific patterns of molecular changes linked to brain ageing.

Mezer tells Physics World that the information they used can be obtained with current MRI machines and that calculating the molecular lipid signature from the qMRI measurements is relatively easy – the required code is available online. He adds that the main issue is the time that qMRI measurements take, compared with standard MRI scans. “Nowadays, there is a great effort in the MRI field to make it faster,” he says. “Nevertheless, time is a real issue for daily clinical use.”

Quantum teleportation, FLASH radiotherapy and the end of electricity from coal

Researchers have been raising the bar for quantum teleportation as Susan Curtis explains in this week’s podcast. While standard quantum teleportation has been limited to particles with just two states, the latest results set the technique on a trajectory for teleporting more complicated systems.

Also in the news this week, Margaret Harris reveals the conclusions of a study on the possible impact of visa restrictions for start-ups, who hope to attract the most suitable candidates for a highly specialized work force.

We get some of the scoop from the American Association of Physicists in Medicine (AAPM) Annual Meeting as Tami Freeman reports back on some of the topics that caught her eye, including FLASH radiotherapy, which uses high dose rates and has been producing some very encouraging results. Anna Demming brings an update from the Advanced Material Show where the prospect of bagging a bottle of chilli sauce in a giveaway finds her in conversation with a company dealing with a totally different kind of heat.

We reveal the results from our reader poll on what poses the greatest challenge to solar cells knocking coal off the hotspot for mains energy generation, and hear from global expert Martin Green who has been working in the field for more than 40 years.

And finally we wrap up with some bubble physics as Susan Curtis reports back on some spectacular soap bubbles that have attracted attention in our Red Folder.

Image courtesy: iStock/agsandrew

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