Peeing at the Grand Prix just got a lot more meaningful. In the latest episode of Physics World Stories, Lucy Bell-Reeves and Olivia Wilson, who work for the start-up NPK Recovery, based at the University of the West of England, explain how their mobile system upcycles urine into fertilizer, right where it’s produced.
The pair unpack the physics and chemistry behind their approach, contrasting it with the energy-intensive Haber-Bosch process, which converts natural gas into ammonia under extreme heat and pressure at centralized plants. With the UK importing 100% of its nitrogen, and recent global conflicts exposing the fragility of fertilizer supply chains, the case for local, circular alternatives is growing stronger.
Host Andrew Glester hears about the pair’s experience at the British Grand Prix in Silverstone, the UK’s leg of the Formula 1 World Championship. Bell-Reeves and Wilson reflect on what it’s like to experience the “Grand Pee”, and how attendees react when they discover where their urine ends up.
While not pitched as a replacement for industrial-scale ammonia production, the system offers a smart fix for off-grid sites facing sudden spikes in human waste.
Every breath we exhale carries a complex chemical narrative written in thousands of volatile organic compounds (VOCs). These tiny molecules, produced by human metabolic processes and invading pathogens, hold immense diagnostic potential. Yet, translating this molecular cloud into a definitive medical diagnosis has long faced an analytical bottleneck. Now, an international team of physicists from Botswana and South Africa has harnessed machine learning to decode these complex signatures, offering a rapid, non-invasive pathway to detect tuberculosis (TB) directly from human breath.
Breaking the analytical bottleneck
Traditional gas chromatography-mass spectrometry (GC-MS) excels at separating complex molecular mixtures based on volatility and mass-to-charge ratios. However, a single breath sample generates thousands of overlapping spectral peaks. Manually sifting through this dense landscape is a painstaking, time-consuming process.
To find a faster, more systematic approach to molecule identification, researchers in the Nano –Breath taking group led by George Chimowa from Botswana International University of Science and Technology (BIUST) collected breath samples from three distinct cohorts: patients with active TB, individuals with multidrug-resistant TB (MDR-TB), and healthy control volunteers.
Standard analytical pipelines often rely on aggressive data pre-processing to smooth and simplify the GC-MS spectra. However, this filtering risks erasing subtle, low-concentration molecular features that might hold critical diagnostic clues. Bypassing this limitation, the BIUST group fed a high-dimensional dataset of 1867 spectral features (from 87 breath samples) directly into four competing supervised machine-learning algorithms: decision trees, random forest, k-nearest neighbours, and support vector machines (SVM). The researchers published their findings in Discover Artificial Intelligence.
Geometric optimization avoids the pitfalls of high-dimensional data
The team found that the linear SVM classifier led the algorithmic comparison, distinguishing among the three patient cohorts with 93% accuracy.
This performance stems from how the algorithm handles high-dimensional data spaces. While distance metric models often suffer from overfitting errors, where experimental noise is misidentified as a meaningful diagnostic signal, SVM relies on geometric boundary optimization to separate classes.
Much like clearing a wide highway down the centre of two opposing crowds, it identifies a hyperplane that maximizes the margin between groups. Instead of tracking every individual in the crowd, the algorithm relies solely on a sparse subset of border points known as support vectors. By focusing strictly on these boundary “guards” and ignoring the background movement, this approach completely isolates the classifier from the noise inherent to the surrounding high-dimensional feature space.
Beyond raw classification accuracy, the model yielded a crucial insight for future clinical applications. It pinpointed a specific window within the gas chromatogram, a retention time between 10 and 30 min, where the most diagnostic, high-variance VOCs elute. This 20-min window corresponds to medium- and large-molecule VOCs, including specific chemical biomarkers associated with TB, such as tridecane, decane and O-cymene.
By demonstrating that these vital diagnostic features are concentrated within this single slice of data, the physicists have shown that future diagnostic hardware can be specialized, eliminating the need to analyse the entire spectrum. Narrowing the focus to this specific elution window can drastically shrink data-processing times and maximize instrument throughput in clinical settings.
AI and the future of medical diagnostics
TB remains one of the world’s deadliest infectious diseases. Traditional diagnostics rely heavily on slow sputum cultures and backlogged laboratory queues, delaying critical treatment. A rapid, non-invasive breath test powered by an optimized physical classifier offers an ideal alternative for resource-limited settings where laboratory infrastructure may be scarce.
While the researchers emphasize that larger validation trials are required, the work signals a profound shift in medical diagnostics. It mirrors advanced data-modelling techniques used in engineering, such as those predicting structural degradation in self-healing aerospace composites.
By fusing analytical physics with artificial intelligence, this research points to a future where immediate, automated bedside disease detection could be rapid, accessible and driven entirely by the mathematical profiling of a patient’s breath.
If you’ve ever kept a drink cool on a hot summer day by placing it inside a frozen, gel-filled sleeve, you’ll understand the appeal of phase change materials (PCMs). The reason these sleeves work so well (and so much better than simply putting your drink in a cold bath or cool room) is that the solid inside them has a high latent heat, meaning it can absorb relatively large quantities of energy before melting and beginning to warm up.
But what if surrounding your drink with a frozen PCM isn’t enough? What if you want to cool your drink more quickly and evenly? One option would be to create a PCM sleeve with fin-shaped extensions that protrude into your drinking vessel. These fins would cool your drink – or, equivalently, allow your drink to melt the PCM – much more efficiently than a simple sleeve. But what should the fins look like? How far apart should they be? And how many of them do you need?
These are the questions that Paolo Proia, Mauro Sbragaglia and Giacomo Falcucci considered in a study published in EPL– though not with the aim of keeping their drinks cold. As researchers at the University Tor Vergata of Rome, Italy, Proia, Sbragaglia and Falcucci are interested in PCMs that store and release heat like a battery. Such materials are useful in fields such as electronics and refrigeration where heat is a common byproduct. Other applications include maintaining the efficiency of solar panels by preventing them from getting too hot and keeping buildings cool in the daytime via insulation.
Physics World spoke with them about their work.
What was your motivation for doing this research?
Our interest in PCMs stems, in part, from our interest in their many applications, especially in the ecological transition to less carbon-intensive fuels. PCMs are particularly good at managing heat in hydrogen storage with metal hydrides, for example, because storing hydrogen in these materials produces heat, while releasing the hydrogen requires it. Using a PCM to store the heat of the adsorption process and give it back during the release means that the produced heat doesn’t go to waste. Instead, it improves the efficiency of the process.
We’re also fascinated by the complexity of the equations involved. The coupling of fluid and temperature dynamics already causes interesting phenomena such as convection. By adding a phase transition to the mix, you introduce a moving boundary that complicates the system even more, both phenomenologically and analytically, since the describing equations must account for it.
We started this paper as a way of extending our previous work on the insertion of fins inside a PCM to three dimensions. PCMs are exceptionally good in latent heat but severely lacking in sensible heat; in other words, they store heat well, but they absorb and release it poorly. Fins are useful in relieving this flaw since they enhance the heat transfer surface and provide a horizontal heat source, which is instrumental for the development of convection, the main driver of heat transfer in this kind of system. By switching to a 3D system, we had more freedom to explore complex layouts of multiple fins and the importance of their relative position.
Phase change modellers: (left-right) Paolo Proia, Mauro Sbragaglia and Giacomo Falcucci. (Courtesy: Paolo Proia)
What is the most important advance in the paper?
The most important result is that naively inserting fins too close to each other can cause interference. If there are overlaps in the fins’ “influence zone”, the system will waste energy by, in effect, trying to melt something that was already molten from heating by a nearby fin. Moreover, by comparing a single fin and multiple fins with the same total surface, we found that the latter configuration benefits from the gaps between the fins. This is because the substance in these gaps melts early and starts acting as an extra heating surface, contributing to the development of bigger convective structures.
Why is it so challenging to model melting in phase change materials in 3D?
Beyond the analytical requirements we already mentioned, the success of this type of modelling depends on having a resolution that is high enough to capture correctly all the phenomena in the system. This means the number of computational sites N must be sufficiently large. In 2D, we “only” have N2 sites to model, but in 3D, this scales to N3. That creates a challenge because making N too large would severely slow down the simulation. Moreover, we must be sure to respect the restraints on the physical parameters for which the lattice Boltzmann method is a correct approximation of the equations involved. So, we underwent a thorough validation process to pinpoint the best parameters for the algorithm.
What do you plan to do next?
First, we’d like to further optimize the code. The main bottleneck is the speed of a single iteration. Ideally, we’d like to study a wider range of layouts and physical conditions, but with the code we have now, that would impact heavily on performance. For example, a slower-melting substance requires more iterations to completely melt, which translates into more real-life time to model, sometimes outside the limits of feasibility. This problem would obviously be solved if we can make a single iteration faster.
Another issue we have is that some ranges of physical parameters can make the simulation unstable. Fortunately, there exist some remedies to this, and we plan to eventually adopt them.
Finally, we would be happy to see other researchers use these findings in their own optimization studies on fin shapes and spatial layouts. It would also be very interesting to see someone study this problem from an analytical angle or to see some experimental validation. In the medium term, we are planning to conduct our own experiments to use as a benchmark for our computational results.
Pressure-dependent degradation mechanisms Low stack pressure accelerates cathode cracking, while high pressure promotes lithium plating. At the optimal pressure, balanced interparticle contact and porosity minimize mechanical degradation. (Courtesy: CC BY 4.0/Nat Energy 10.1038/s41560-026-02087-6)
Engineers are constantly striving to improve the safety and performance of electric vehicle (EV) batteries. Much effort has been put into developing new electrode materials over the years, but future improvements may not follow the same path and may just be as simple as utilizing physical pressure.
A recent study, led by researchers at the University of Cambridge, suggests that EV batteries could be made to last up to twice as long, by applying the right amount of pressure to the electrodes. It is, however, a fine balancing act, as too high or too low a pressure can cause the battery to fail. To employ this approach in real world systems, engineers will need to make sure that the process is easily repeatable without significant pressure error, but it’s an interesting avenue of battery engineering that has come to fruition.
“We carried this work out to improve the sustainability of batteries,” says Michael de Volder, one of the lead researchers on the study. “Given that we are not very good at recycling batteries, extending the lifetime of batteries reduces the need for mining critical minerals for making new batteries and therefore improves their sustainability.”
For their study, reported in Nature Energy, the researchers developed a dilatometer with pneumatic bellows to apply pressure to the electrodes. The bellows act like a clamp to maintain a uniform and constant pressure on the electrode, while a sensor detects small volume changes that occur as the battery charges and discharges.
The researchers tested their electrode pressurization approach on commercial nickel manganese cobalt (NMC) lithium-ion pouch batteries (which have a flexible packaging), without changing their electrolyte or electrode composition. By using commercial batteries with a standard setup, they could test them fairly under different pressures.
“In this work we optimized how hard battery anodes and cathodes should be pushed together to maximize the lifetime of batteries,” de Volder tells Physics World. “Importantly, we also unravel which degradation mechanisms kick in if you press too hard, or not hard enough.”
Doubling battery lifetime
The researchers found that increasing the stack pressure fourfold over typical initial values used in conventional coin cells – to an optimal pressure of 12.5 bar – doubled the lifetime of the NMC811 cells. They compared the results with NMC cells tested at an extra-low pressure of 1.5 bar, a low pressure of 3 bar, a medium pressure of 6.5 bar and a high pressure of 37.5 bar.
Different degradation mechanisms emerged at high and low pressures outside of the optimal pressure zone. Low stack pressure accelerated cathode cracking, causing an increase in transition metal dissolution and excessive formation of the solid electrolyte interphase (SEI) layer. The cracking is likely due to a small number of particles bearing most of the mechanical load, leading to localized high-stress concentrations that initiate crack propagation.
Higher stack pressures, meanwhile, caused increased lithium plating on the anode. The team observed that the electrode thickness reduced during initial cycling but then underwent rapid thickness growth. When the electrodes are at their thinnest, they have a lower porosity that limits lithium transport, leading to higher overpotentials and higher lithium plating. This increases the amount of “dead” lithium and reduces the usable lithium inventory in the battery, causing it to degrade faster.
“We found that when the pressure applied to battery cells is sub-optimal, certain dangerous degradation processes can be accelerated. So, in a way, pressure optimization might improve the safety of batteries. However, more research is needed before we can draw reliable conclusions on this front,” says de Volder.
The pressurization results in this study are still in the early stages, but if shown to be viable at scale in commercial systems, could help EV batteries to last longer. In theory, this could give second-hand EVs a higher market value as the vehicle will have a longer battery life when sold. Additionally, if EV batteries can last longer, it will reduce the pressure on lithium mining operations and reduce the amount of raw material required for battery manufacturing (assuming the same demand) – something that is becoming an issue due to the skyrocketing price of lithium.
Cambridge Enterprise, the university’s innovation arm, has filed a patent, so the research team and university obviously see commercial viability in the process. When asked about the team’s future plans, de Volder tells Physics World that “we studied pressure optimization for one specific battery chemistry, but we anticipate that gains can be made in the lifetime of other battery chemistries too”.
This episode of the Physics World Weekly podcast features Antonia Seymour, who is chief executive of IOP Publishing.
Seymour has more than 30 years’ experience in a publishing industry that has evolved significantly from the days of paper journals to today’s sophisticated digital technologies.
In this interview we explore how scholarly publishers are responding to the rapid growth in research output, the rise of artificial intelligence and the increase in threats to research integrity.
A wholly owned subsidiary of the Institute of Physics, IOP Publishing produces more than 100 scholarly journals as well as Physics World.
The STFC cuts come after the council announced late last year that its core annual budget would rise by only £7m to £842m over the four years from 2026 to 2030. One of seven research councils within UK Research and Innovation (UKRI), the STFC runs the UK’s national facilities and supports particle physics, astronomy and nuclear physics (PPAN) research in the UK.
In a strongly worded statement, IOP president Paul Howarth is now urging the government to review “this ruinous set of decisions”, calling the cuts a “terrible blow” that will do “real damage” to the UK’s scientific reputation and put future economic growth at risk.
“Despite reassurances, physics has not been protected, crucial facilities remain under threat and jobs are being lost,” says Howarth. “Scientific capability that has taken years to build up is being put at risk by these decisions – it undermines a number of our most important international collaborations and could put a whole generation of young people off a career in science.”
Balancing the books
Although UKRI has received a record £39bn investment across the four-year period, it said last year that projects at STFC would need to be cut given inflation, rising energy costs as well as “unfavourable movements in foreign exchange rates”. Together, the STFC’s annual costs are projected to rise to over £1bn per year by 2030, forcing it to find ways to balance its books by 2029.
Earlier this year, the STFC said it would have to cut its core science budget by at least 30% over 2024/2025 levels. UKRI also noted it would stop funding two UK facilities – the Relativistic Ultrafast Electron Diffraction and Imaging facility and the C-MASS mass spectrometry centre. A UK-led upgrade to the LHCb experiment at CERN and support for the Electron–Ion Collider at Brookhaven in the US would be axed too.
That announcement caused significant distress within the physics community, prompting the heads of UK university physics departments to publish an open letter to then science minister Patrick Vallance, expressing their “deep concern” about funding changes adding that such cuts cause “reputational risk”.
UKRI then carried out further consultation with researchers and the STFC’s expert advisory bodies, with the results of this “funding prioritisation exercise”now revealed. There is some good news for STFC-funded “discovery-led” PPAN research, which physicists had feared could be cut by a third. Following lobbying, UKRI says this work is being “protected”, although it will still fall by 2.7% over the next four years.
Under attack
While facilities such as Diamond Light Source, the ISIS Neutron and Muon Source, and the Central Laser Facility will not be mothballed, the STFC’s budget for multidisciplinary facilities will reduce by 15% over the next four years to save £28m. As a result, ISIS will have to reduce operational time at the facility.
Yet the STFC warns that if saving and income targets for the programme are not met by 2028 then further action could be taken, which could involve closing a multidisciplinary facility.
STFC’s national laboratories and estates budget fares slightly better, falling by 8% over the four-year period, but individual facilities will be hit harder. The operational budget of the Boulby Underground Mine, for example, will be slashed by 40%.
Particle fever
The STFC insists that subscriptions for international projects, such as CERN and the European Southern Observatory, will remain protected despite their costs expecting to rise by 19% over the next four years. But other projects, including the EIC as well as the LHCb upgrade, will not be funded. The latter is expected to operate until 2033 by which time it would have reached the end of its lifetime after years of intense radiation damage.
An upgrade was planned so that it could take advantage of the upgrade to the LHC – the High-Luminosity LHC (HL-LHC) – and offer an order of magnitude increase in luminosity over upgrade I.
Down and out? UK funding for a major upgrade to LHCb has been cancelled increasing the possibility that it won’t go ahead. (Courtesy: CERN)
Tim Gershon from the University of Warwick, who became international spokesperson for the collaboration this month, says that the outlook for STFC-funded science is “grim”.
“With a 15% cut last year and an outlook that sees funding shrink further due to inflationary pressure, not even excellent-rated and internationally-leading science like LHCb can be supported,” he adds. “LHCb is the canary in the coalmine for the future sustainability of particle physics and astronomy research.”
Gershon states that the decision to cut UK involvement in LHCb will throw away the leadership it has built up. “Not only is this a tragedy for researchers and engineers who have dedicated their lives to making LHCb one of the most successful experiments in history, it destroys opportunities for current and future students to be involved in world-leading scientific discovery,” he adds.
This is a short-sighted move, to save a tiny fraction of the overall UK science budget
Catherine Haymans
Gershon says it will take some time to understand what the UK’s decision means for the upgrade and how other funding agencies will react but without UK expertise it will be hard to progress given the UK is the largest partner in LHCb with a 20% stake.
“Ultimately, the LHCb Upgrade is an essential part of the full exploitation of the HL-LHC, which is the top priority of the European and CERN strategies for particle physics,” adds Gershon. “We are determined to deliver the best detector that is possible within the available resources. But such a major change to the level of expected resources makes this extremely difficult.”
Peter Millington, a particle physicist from the University of Manchester, says that the outcome is “bad news” for accelerator physics and the applications that it fosters, particularly in medical physics. “It is completely at odds with UK priorities across all industrial strategy growth-driving areas, while also eliminating skills pipelines pivotal to a wide range of sectors and eroding the UK’s long-held position as a global scientific leader.”
Astronomy woes
Astronomy is another area that is bearing the brunt of the cuts. The UK contribution to the e-MERLIN network of seven radio telescopes, which includes the iconic Lovell telescope at Jodrell Bank in northern England, is also ear-marked for cancellation. Its funding will now run out in 2028 and the move not only threatens e-MERLIN but also the future of Jodrell Bank , which the Royal Astronomical Society calls a “deeply troubling development”.
Catherine Haymans, Astronomer Royal for Scotland, says she is “absolutely devastated” for those working on e-MERLIN. “This is a short-sighted move, to save a tiny fraction of the overall UK science budget,” she says. They are now considering contacting the new Department for Business, Innovation, Science and Trade to reverse the decision.
Other astronomy cuts include the UK withdrawal from the James Clerk Maxwell Telescope located in Hawaii as well as 20% cuts for the UK’s Square Kilometre Array Regional Centre and activities at the Vera C Rubin Observatory in Chile, which recently began a 10-year survey of the universe.
Jim Wild, president of the Royal Astronomical Society, notes the cuts are “devastating news” for UK astronomy. “At a time when technological innovation is crucial to our country’s prospects, discarding unique, globally significant observatories threatens both our scientific future and the inspiration of future generations of astronomers,” adds Wild.
Michele Dougherty, executive chair of the STFC, who is also Astronomer Royal, says that the situation requires “tough, but necessary decisions”.
“After listening to our community we have protected core discovery research within PPAN, through a more focused portfolio that safeguards postdoctoral researchers, protects PhD opportunities and maintains the UK’s international leadership.” adds Dougherty, who stepped down as president of the IOP in January over the conflict of interest with her position at the STFC. “These are never easy choices, but we have made what we feel are the right decisions to bring STFC to a sustainable financial position by 2029/30″.
A few years ago, I was lucky enough to see the Bayeux Tapestry – the famous embroidered cloth depicting the Norman invasion of England in 1066. More than 900 years old, this historic piece of art is only 50 cm wide but more than 68 m long. It’s also extremely fragile, which why I was astonished when I heard that the Bayeux Tapestry was going to leave its home in Normandy and be transported across the English Channel to the UK.
I’m fascinated by how non-invasive optical techniques have been crucial in advancing our understanding of the tapestry
So what’s all this got to with physics? Well, I’m fascinated by how physics – and specifically, non-invasive optical techniques – have been crucial in advancing our understanding of the tapestry and its historical significance. Thanks to physics-based equipment developed by hi-tech manufacturers, we’ve learned about how the Bayeux Tapestry was initially made, what damage it subsequently suffered, how it was repaired, and the nature of its current condition.
Such information is vital not only for increasing our historical awareness, but also for current conservators who want to understand the tapestry’s underlying condition and find out how to preserve it for future generations. And before the pedants write in, yes I know that while it’s known as the Bayeux Tapestry, technically it’s an embroidery. That means it was created by stitching woollen threads onto a linen backing, which is helpful to know when reviewing the physics involved.
Optical sleuthing
The beauty of using optical methods to study the Bayeux Tapestry is that they are non-destructive and non-intrusive – and so can typically be applied in situ. In 2017 a three-year project was started, in which conservationists used high-resolution 2D imaging, photogrammetry, multimodal scanning and advanced image reconstruction techniques to determine the tapestry’s condition and conservation needs. The project revealed considerable information about how this artwork was created and modified over time.
Thanks to these high-resolution images, we now have a single digital map of the entire tapestry, making it possible to zoom in and look at individual threads. It’s yielded information such as the width of stitches and the positions where the wool threads cross the original linen background. As a result, historians now believe the tapestry was made by a single group of embroiderers, who – knowing the skills that existed at the time – were probably based in Canterbury, UK.
Techniques such as infrared spectroscopy and fluorescent and reflection ultraviolet imaging have revealed information about what’s underneath the surface of the tapestry
From the size and direction of the stitches, we also think the outlines of the figures were stitched first, with the shapes filled in afterwards using coloured wools in a strict, specific order. Meanwhile, techniques such as infrared spectroscopy and fluorescent and reflection ultraviolet imaging have revealed information about what’s underneath the surface of the tapestry. In particular, they’ve located the presence of stains such as glue, wax (dripped from candles that lit the tapestry) and even oil from the hands of people who touched it.
Infrared light passing through the dark-coloured wools have also revealed original sketch lines that were drawn on the linen base before the wool stitching started. It reveals the original artist’s draft, likely to be someone familiar with manuscript drawing – perhaps an illuminator of religious books.
Researchers in France, led by Stéphane Le Mouélic from Nantes University, who originally did a PhD in astrophysics, have also used computer software to combine more than 440 overlapping 2D photos taken from multiple angles to create a detailed 3D model of the Bayeux Tapestry (J. Cult. Heritage71 211).
It digitally “irons out” all the sags and wrinkles in the line fabric, recreating the original, “flat” tapestry and allowing the original physical shape of the artwork to be revealed for the first time. The 3D model can be viewed for free at the Bayeux Museum website, allowing historians, researchers and members of the public to study it without having to handle the delicate material.
Physics-based techniques have also allowed us to deal with the fact that parts of the fabric have been repaired over the last 900 plus years. Some of those repairs used non-authentic dyes and colours, while others covered up the original stitching. But using computer vision and image processing, threads that were added later can be subtracted digitally, providing a clearer, corrected view of what the original tapestry looked like.
Finally, optical tools can help keep the tapestry safe for future generations. Museum curators need to know if the cloth is sagging, tearing, or changing shape over time. Instead of putting heavy tools on the cloth, lasers can scan the cloth to accurately map of the contours of its surface. By repeating this exercise every few years, conservationists can spot if any part of the cloth has stretched or sagged, enabling minor problems to be rectified before they end up causing significant damage.
Without the huge amount of investigative and restorative work carried out, the Bayeux Tapestry would never have been allowed to make the journey to London
In 2025 Le Monde newspaper reported that experts had, over the previous five years, meticulously documented 24,204 stains, 9646 holes and 30 tears in the artwork. Without the huge amount of investigative and restorative work carried out, the Bayeux Tapestry would never have been allowed to make this year’s journey to London. Advanced and detailed optical measurement has “de-risked” the tapestry’s trip.
Quantum theory is one of humanity’s great intellectual achievements, radically transforming our understanding of nature at the deepest level while delivering unprecedented technological advances. We have thus always felt it a great pity that most young people never get the opportunity to engage with the theory at a substantive level.
The solid-state physicist David Mermin, who has studied the fundamentals of quantum mechanics, once memorably wrote of quantum theory: “We now know that the Moon is demonstrably not there when nobody looks”. It was a comment that certainly captures the imagination, but it is difficult to appreciate what he meant meant without engaging with the mathematics that lies behind it.
In an attempt to see if we could change that, we ran our first Quantum in Pictures programme at the University of Hertfordshire earlier this month. A five-day, in-person course, it was attended by about 45 students aged 16–18 and was built around Quantum Pictorialism – a diagrammatic approach to quantum theory pioneered by Bob Coecke from the University of Oxford and collaborators.
Seeing for real Bob Coecke using his pictorial approach to the subject (Courtesy: Shanti Pise and Leron Borsten)
The crucial point is that the pictures aren’t illustrations of some more fundamental mathematics hidden underneath. The pictures are the mathematics. A rigorous graphical calculus built from spider diagrams enables students to reason directly about quantum processes. Since this diagrammatic formulation is fully equivalent to the usual Hilbert space formalism, the students were doing quantum mechanics for real.
We felt truly privileged to share the mysteries of quantum mechanics with a fantastically friendly, interested and diverse cohort from schools across south-east England. What struck me was how readily they engaged with the material: asking excellent (and sometimes rather challenging) questions, debating ideas and working collaboratively through the problem-solving sessions.
The graphical problems proved particularly popular, with repeated cries for “more spider diagrams!”. The course was deliberately ambitious, but by the end, they were able to work through the complete quantum teleportation protocol. Indeed, one student was confident enough to get up and reason through it for the whole class (something we certainly would not have dared to do at their age).
As Maya, a year-12 student from Highams Park Sixth Form in London, put it: “I really enjoyed seeing how ideas in quantum physics could be explained through simple pictures and diagrams. I was surprised that concepts like quantum teleportation, which seemed very complicated at first, could become much easier to understand through this approach. The programme has made me even more interested in studying physics and exploring quantum theory in the future.”
The approach also worked for students without a traditional mathematics or physics background, such as Andrew, a year-12 student from Sir John Lawes School in Harpenden.
“The programme was captivating,” he said. “The concept of using diagrams was innovative and explained things in a logical manner to help me understand topics such as quantum teleportation. The programme showed the stark differences between classical and quantum physics through real-world examples, enriched by talks from industry experts and pioneers with different backgrounds.”
Muhammad Hamza Waseem, who helped develop the programme and joined us on the final day, captured the atmosphere perfectly. “I found the enthusiasm, curiosity, and irreverence of the students very inspiring,” he said, “and I hope that they take the same spirit into their university education and beyond.”
That sense of joy and excitement was, for me, the lesson of the week. We’ve been thoroughly convinced that quantum theory isn’t intrinsically beyond the reach of curious 16-year-olds. We just need to give them the right mathematical language. The next step is an optional graduate-level exam, which will put that claim to the test. Watch this space.
The authors would like to thank staff, researchers and students from the University of Hertfordshire who volunteered their time to make the programme possible. They are also grateful to Ian Loffler, Bob Coecke and Muhammad Hamza Waseem for their support and inspiring contributions.
Science is often easier to learn and understand when its abstract ideas are presented through the lens of our everyday world. Indeed, a key challenge for science teachers is to make the subject as interesting as possible to students, usually by showing its applications to real-world problems. As a former college lecturer turned science journalist, Trisha Muro is very well suited to this task.
To introduce her new book It’s (Just) Rocket Science: Exploring Physics Through Spaceflight Missions, Muro recalls how, while teaching high-school physics, she had a student drop out of her course because they “thought it would be more like ‘story’ physics”. Muro wasn’t exactly sure what the student meant, but the phrase stuck with her over the years, eventually leading her to write this book. Within its pages, Muro presents quintessential physics concepts in the context of spaceflight. She touches upon everything from the Apollo space programme to the Mars rovers, to provide the narrative aspect that makes abstract science relatable.
I’d argue that rather than story, the examples she uses in the book are more like case studies, as there is not much of a continuing narrative. Indeed, I couldn’t help but wonder if by “story”, Muro’s student meant science-fiction physics rather than real-life examples, but that’s semantics. What Muro has written is a very effective guide to all manner of basic physics that draws upon all her experience as a physics teacher and all her skills as a science writer.
In It’s (Just) Rocket Science, each chapter features an interview with one or two scientists (refreshingly, mostly women) providing insights into how the missions that they work on employ physics. There are some clear and concise explanations and neat analogies throughout. Muro provides a treatise on general relativity by highlighting the Hubble Space Telescope’s observations of gravitational lensing. She also includes a fascinating explanation of momentum via the physics of NASA’s DART mission, which impacted and deflected the little asteroid Dimorphos. Muro’s description of the electromagnetic spectrum is aided by discussions about interplanetary radio communications, the spectroscopic measurements of Venus that the forthcoming DAVINCI mission will make, and the X-ray vision of the Chandra Observatory.
The chapters I enjoyed best were in part two of the book where, as a self-confessed Space Cadet, Muro talks about how she attended a NASA Space Camp in the 1980s. (She is donating 100% of the proceeds from this book towards funding scholarships for children to attend the camp too.) In this section, Muro takes us through the science of rocket launches and landing on other worlds. She explains how the balance of forces as described by Newton’s laws of motion will enable NASA’s Dragonfly helicopter mission to fly on Saturn’s moon Titan. I especially liked the ice-skating analogy that Muro used to describe gravitational slingshots. Imagine two ice skaters, one being yourself and the other a champion speed skater, writes Muro. You get a head start, then the speed skater races up alongside you, takes your hand just for a moment and then lets you go, giving you an energy boost.
Muro gets through an impressive amount of science in a short space – the first 50 pages alone are full of heavy topics such as Kepler’s laws of orbital motion, planetary transits, exoplanet science, Lagrange points, gravitation, the three-body problem, general and special relativity, the concept of space–time, the speed of light, the Doppler effect, and even an equation or two. Phew! That’s a lot of science, and while at times it might feel dense to the uninitiated, at no point is it too confusing or impenetrable for the science or space enthusiast.
Muro’s willingness to include equations (there are even two interludes featuring derivations) reminds us of her teaching background. I found it refreshing to see maths presented front and centre when most popular-science books shy away from it, in an attempt not to lose readers. In this book, the maths isn’t complex and it is crucial in showing us why various physical laws work the way that they do.
One small issue for me was Muro’s decision to incorporate both imperial and metric units, which made for some confusing reading. In some instances, she mixes the systems in the same sentence – for example, giving a distance in kilometres followed by a weight in pounds, or a speed in miles per hour followed by energy in joules. Muro comments in the chapter about momentum and the DART mission that she has been using both systems to help readers become more comfortable with them. However, if the conversions between imperial and metric are not going to be given, then I’m not sure she really succeeds at making people more comfortable using metric.
If I were to nitpick further, I’d point out that when Muro strays from straight physics and engineering to astrophysics, some mistakes do crop up. These include stating that objects in the early universe are “red” because they have been cooling for billions of years. What is really happening is we are seeing them as they were long ago and their colour is the product of cosmological redshift, not temperature. Another is implying that gravitational waves are what cause the orbits of asteroids and comets to be perturbed. This ignores the fact that gravitational interaction from the planets, particularly Jupiter, is the dominant influence. However, these errors do not detract from the otherwise clear and correct explanations of the physics, which are easy to read and pitched perfectly for students below university level.
Overall, It’s (Just) Rocket Science is an excellent book that turns abstract physics into something more relevant. With the popularity of the recent Artemis II mission, the book’s focus on space missions will hopefully help it find an audience who will really take all that Muro has to teach on board.
2026 Johns Hopkins University Press £25.50 hb 384pp
Many catalysts are made using core-shell nanoparticles, in which the core is a structurally important or inexpensive material and the thin shell surrounding it is an expensive metal such as platinum. Since catalytic reactions occur on the surface, this helps to reduce the amount of platinum required and therefore lowers costs. Crystal structures are described based on the smallest repeating unit of the crystal (the unit cell) using the Bravais lattice system. Three important crystal structures are face-centred cubic (fcc, atoms at the corners and faces of a cube), body-centred cubic (bcc, atoms at the corners and centre of a cube), and hexagonal close-packed (hcp, a hexagonal arrangement of atoms).
Different materials have different crystal structures; for example, platinum is fcc, many alloys are bcc, and magnesium and zinc are hcp. In core–shell nanoparticles, differences between the crystal structures of the core and shell mean that the atoms do not line up perfectly. This mismatch creates strain, which can significantly affect catalytic performance. In this work, the researchers explored how a platinum shell grows on a different crystal structure in a process known as heteroepitaxy.
They studied platinum shells (Pt, fcc) grown on cores made of ruthenium (Ru, hcp), palladium–copper (PdCu, bcc), and specially synthesised ruthenium with an fcc structure. It was found that each system accommodates the atomic mismatch differently. In hcp/fcc particles, some areas lined up coherently while others contained defects called dislocations, which formed networks in particles smaller than 10 nm. In bcc/fcc particles, both the core and shell stretched or compressed to fit together. In fcc/fcc particles, the matching crystal structures aligned more readily, but twin defects formed in which one region mirrored another.
Overall, this study shows that the way a Pt shell grows on a nanoparticle core is determined by a balance between the energies of the interface, shell, and core, with the system naturally adopting the lowest-energy configuration. These findings could help scientists achieve atomic-precision interfacial engineering, controlling the catalytic, mechanical, and electrical properties of core-shell nanoparticles.
Quasicrystals are unusual yet relatively common materials. They show up in lots of different places from alloys to colloids and even in meteorites. They have some ordered structure, but unlike ordinary crystals their patterns never repeat.
This mix of order and irregularity leads to interesting behaviour when waves move through them. In optical versions of these materials, light can become trapped or guided in ways that doesn’t happen in regular structures.
In a new study published recently, a team of researchers investigated what happens when light beams with a twist, called vortex beams, travel through quasicrystals that have been deliberately altered. They began with a classic pattern known as the Penrose tiling and then introduce large scale defects by removing or adding wedge shaped sections. This let the researchers tune the rotational symmetry of the structure and compare how light behaves in each case.
Using a standard model for how light travels through the material, the researchers showed that these modified quasicrystals can support new vortex states. These include two distinct types of vortex solitons, which are twisted beams of light that keep their shape as they travel rather than spreading out.
Usually, these light states require carefully tuned input power and are easily disrupted. What’s different in this case though is they form even with weak input and remain stable under small disturbances. This makes them far more applicable to real-world conditions.
These vortex beams can carry information in the amount of twist they have, providing an extra way to encode data alongside commonly used properties such as intensity or colour. If they remain stable as they travel, they would allow more information to be sent through the same optical system. This could be very useful in optical communication systems, where fast and efficient data transmission is essential.
A new method of stabilizing radioactive molecules could open the door to sensitive searches for physics beyond the Standard Model. The approach, which involves cooling radium-bearing molecules to just above absolute zero, offers a tabletop alternative to experiments that use particle accelerators to look for violations of fundamental symmetries. According to lead researcher Nick Hutzler, a physicist at the California Institute of Technology (Caltech), US, it also shows that university laboratories can safely handle these radioactive materials, paving the way for similar studies at other institutions.
One of the greatest puzzles in physics is the fact that the early universe created more matter than antimatter. For decades, physicists have tried to solve this mystery (and others) by using particle accelerators to search for violations of nuclear symmetry at ever-higher energies. However, molecules that contain heavy radioactive nuclei could also act as super-sensitive sensors for symmetry violations – with the advantage that the equipment required to manipulate them generally fits in a single room, rather than an entire building.
Pear review
The basic idea is this: when electron orbitals overlap with a nucleus, the system’s atomic or molecular energy levels shift by tiny amounts that depend on the nucleus’ size and shape. Variations in nuclear structure due to symmetry-violating effects would therefore produce changes in the electron orbitals, and these changes could be measured with high-precision spectroscopy.
Asymmetric nuclei are ideal for this purpose because their lopsided shape makes small changes easier to detect. Radium, for example, has a pear-shaped nucleus, and radium-containing molecules offer additional advantages because the repulsion and attraction of neighbouring atoms further distorts the electron orbitals.
The downside is that radium is both radioactive and highly reactive, making it dangerous to handle without specialized equipment that is not present in standard university laboratories. It is also only available in extremely small quantities.
Sweet as candy
In the latest study, which is published in Science, physicists at Caltech and chemists at Johns Hopkins University and Michigan State University (all in the US) found a possible way around these obstacles. Their first step was to make radium stable and transportable. For this, they developed a process that resembles candy-making, though they do not recommend eating the results. By “caramelizing” small amounts of radium-226 in a solution of xylitol sweetener, they created a material they could transport in small quantities, keeping radioactivity levels low enough to comply with standard radiation-safety frameworks.
Next, they added their sticky radium “goo” to gold foil; installed it in a copper cryogenic cell; and cooled it to 4K using helium gas. They then used a laser to excite the radium into a chemically reactive state, allowing it to bond with targets such as hydroxide, deuteroxide and fluoride. Collisions with surrounding helium atoms further cooled these radium-bearing molecules into a mixture of only a few rotational and vibrational states. At this point, the team was finally able to perform the first-ever high-precision spectroscopic analysis of such molecules.
Opening doors
Hutzler acknowledges that several challenges remain before precision searches for symmetry violation can begin in earnest. Though theory predicts that these radium-bearing molecular species will be amenable to standard laser cooling and trapping techniques, no one has yet cooled them to ultracold temperatures. Another challenge will be to extend the process to other isotopes. Radium-225, for example, has a better nuclear shape for high-precision searches for symmetry violation, but it is also much more radioactive than radium-226, with a half-life of 15 days rather than 1600 years.
The team is also interested in studying the spectra of other radioactive species, with the aim of better understanding nuclear structure and chemistry at the extremes of the periodic table. A final possibility, Hutzler adds, would be to study other radium-containing molecules, as this would enable different precision measurements.
David DeMille, a physicist at Johns Hopkins who studies symmetry violations in atomic and molecular systems but was not involved in this research, calls it an “extremely promising way” to search for interactions that violate charge-parity (CP) symmetry. The efficiency with which the team converts solid-phase radium atoms into gas-phase molecules is a good sign, he adds, and extending the process to other radioactive molecules could help scientists understand species that have been observed astronomically.
However, DeMille points out that achieving ultracold temperatures poses additional challenges, including finding a way to release the confined molecules into a larger, much more complex experimental setup, without helium, while maintaining safe conditions. That said, he notes that the spectroscopic results are, in themselves, an important step towards reaching this ultracold regime.
A new type of “photonic multi-lane highway” that can carry multiple topologically-protected optical signals at once – without the need for a bulky insulator – has been demonstrated by researchers in China. The technology, which relies on a new type of material called a photonic valley half-semimetal to achieve topological protection, is currently at the prototype stage. However, the researchers believe that, if fabrication challenges can be addressed, the combination of spatial efficiency and topological robustness could be promising for future photonic technologies.
In the past 20 years, photonic topological insulators have become widespread for connections in devices such as on-chip photonic circuits because their edge modes can only conduct light in one direction and are therefore are inherently immune from scattering off imperfections. However, the protected edge mode of a topological insulator comes at a cost: the bulk must have an optical band gap, which means it must be opaque to the relevant frequency. Meanwhile, the photonic analogue of another concept from electronics has also become popular in optical waveguides. Gapless photonic semimetals – analogous to graphene – can be placed between topologically distinct optical insulators to broaden the guided modes, but non-guiding insulating claddings are still required.
To address the fundamental trade-off between spatial efficiency and topological protection in conventional topological waveguides, researchers in the group of Che Ting Chan at the Hong Kong University of Science and Technology in China and their collaborators introduced a novel photonic structure called a photonic valley half-semimetal. Here, the valley degree of freedom refers to inequivalent local energy extrema in momentum space, which can be used as independent degrees of freedom for transport. Crucially, a single photonic valley half-semimetal plays a dual role via its two valley channels: one valley acts as a gapless semimetal that enables waveguiding, while the other functions as a topological insulator that provides a topological barrier for the corresponding valley mode in adjacent regions.
Four stacked layers
The researchers designed a waveguide comprising four stacked layers of a honeycomb structure made from interconnected rods of the magnetic material yttrium iron garnet, which interfered with the propagating photons. By altering the diameters of the rods or the magnetic field, the researchers constructed four inequivalent photonic valley half-semimetal domains and arranged them in a specific periodic sequence. This creates adjacent domains that mutually insulate each other.
Xiaohan Cui is lead author on a paper in Nature that describes the research. She explains that the underlying topological physics is similar to that in a traditional photonic topological insulator.
“The important difference lies in how the mode is spatially implemented,” she says, “In a conventional photonic topological-insulator waveguide, two gapped bulk domains meet at an interface, and the propagating mode is tightly localized to that interface. Most of the surrounding insulating material remains inert, serving only as cladding.”
In the present configuration, however, the researchers were able to use the blocked valley as topological protection for unidirectional propagation in the neighbouring domain, and utilize this to create a four-lane highway, with two lanes in each direction, that could guide signals around sharp bends and through constrictions without backscattering or inter-lane crosstalk:
No wasted space
“The architecture transforms the usual narrow interface state into a set of directly adjacent, large-area waveguiding lanes. Consequently, no region of the device is ‘wasted’ as inert cladding,” explains Cui.
The team’s current device works for microwave radiation but the team says that the design could be adapted and extended to operate at higher frequencies.
“The present experiment is a proof of principle demonstration at microwave frequencies, so one clear next step is to move the concept towards higher-frequency, chip-scale integrated photonics platforms, thereby paving the way toward ultra-compact topological photonic circuitry,” says Cui.
The researchers believe application in the terahertz regime should be possible using magnetized semiconductors such as indium antimonide. However, non-reciprocal applications at higher frequencies could be challenging owing to the weakness of magnetic effects.
“The major experimental challenges will be to realize these higher-frequency designs while managing geometric complexity, fabrication tolerances, and propagation loss, and ensuring efficient coupling with practical sources, detectors and other photonic components,” she explains.
Quantum optician Mahmoud Jalali Mehrabad of Massachusetts Institute of Technology believes the work brings an important issue into focus. “A paper doesn’t always have to have the perfect solution as long as it highlights and really streamlines a key problem…To me this paper does that,” he says. “Spatial efficiency has been a problem in topological physics and the question is why? Is there any other way to destroy this trade-off? It shouldn’t be a side problem in the supplementary material of a paper – this is a big problem.” Whether or not the researchers can make their own solution viable, he says, “time will tell”.
A new measurement of the ground-state hyperfine splitting in antihydrogen shows that it is identical to that of normal hydrogen to within four parts per million – two orders of magnitude more precise than previous experiments. Although the measurement by CERN’s ALPHA collaboration did not reveal any asymmetries between matter and antimatter, the result is nevertheless a milestone in the search for reasons why the universe appears to be made up almost entirely of matter, with only minute amounts of antimatter.
According to the Standard Model of particle physics, all matter particles have a corresponding antimatter particle that is identical to them in every way apart from their charge and magnetic properties, which are reversed. If this model is correct, then the Big Bang that formed our universe nearly 14 billion years ago should have generated equal amounts of antimatter and matter. But in that case, neither we nor almost everything else we observe should exist, because pairs of antimatter and matter particles annihilate each other whenever they collide.
“This apparent lack of antimatter in the universe remains one of the biggest mysteries in modern physics and suggests there is something about antimatter and matter that we do not understand,” says Timothy Friesen of the University of Calgary, Canada, one of the lead authors of a Naturepaper on the new measurement.
Measuring antihydrogen
To look for subtle asymmetries that might explain why matter triumphed and antimatter all but disappeared, ALPHA is performing precise measurements on the simplest antimatter atom: antihydrogen, which consists of an antiproton bound to an antielectron, or positron.
These measurements take place at the CERN Antiproton Decelerator Facility using the ALPHA-2 antihydrogen apparatus, which is designed to prevent antihydrogen from coming into contact with normal matter. It does this by confining the antimatter within a cylindrical Penning–Malmberg trap under an extremely high vacuum and surrounded by strong superconducting magnets. These magnets suspend the antimatter in the trap so that it does not touch the walls of the container it is held in, preventing it from annihilating before measurements can take place.
In the latest work, the ALPHA collaboration focused on a parameter known as hyperfine splitting. This splitting occurs because magnetic interactions between the spins of the antiproton and positron cause the positronic ground state in antihydrogen to split into four sublevels, which the researchers label |a⟩, |b⟩, |c⟩ and |d⟩.
In hydrogen, the magnitude of this hyperfine splitting has been measured extremely precisely – we know its value to within a few parts per trillion – and it is particularly sensitive to the structure of the proton. Measuring this splitting in antihydrogen with the same precision would therefore be an excellent way of searching for differences between matter and antimatter. Previously, however, the most sensitive measurements only managed a precision of 400 parts per million (ppm).
In pursuit of precision
To push beyond this level, the ALPHA researchers applied pulses of microwaves at frequencies between 28 GHz and 31 GHz to induce the positron spin flip transitions |c⟩ → |b⟩ and |d⟩ → |a⟩ between the hyperfine levels of ground-state (2S and 1S) antihydrogen atoms. By measuring the frequencies at which these transitions occurred, they could then calculate the hyperfine splitting energy.
“At a magnetic field of 1 Tesla, we measured the hyperfine splitting for antihydrogen to a precision of 4 ppm – a result that has allowed for one of the best comparisons of matter-antimatter symmetry in antihydrogen ever,” Friesen says.
While the new measurement is precise enough to push experiments into a regime that is sensitive to the structure of the antiproton, Friesen notes that it is still five orders of magnitude less precise than comparable measurements in ordinary hydrogen. “The comparisons at this level of precision with matter hydrogen are identical, and our current models of physics therefore still hold,” he says.
The team does have some ideas for further improvements. “To push the measurement to improved precisions we are aiming to induce antiproton spin flip transitions, since these can be less sensitive to magnetic field inhomogeneities, which are our biggest systematic uncertainty,” Friesen explains. “This, combined with laser cooling the antihydrogen samples to reduce the width of our spectroscopic line-shapes, could help improve the precision by at least another factor of 100.”
At what point does a material become so viscous that it cannot flow? The question is a tricky one because some apparently solid objects are not as rigid as they seem. A glacier, for example, may look immobile, but when viewed over long-enough timescales, its slow flow becomes apparent.
Now, thanks to satellite observations of tectonic plate deformations as well as physical and geodynamic modelling, geophysicist Masaki Yoshida of Ritsumeikan University, Japan, claims to have found an answer. The upper limit for viscosity, he says, is 1028 Pascal-seconds (Pa s), and the new boundary could yield insights into Earth’s geodynamics.
Viscosity is a measure of a material’s resistance to flow. Gases such as air and hydrogen have a viscosity of 10-5 Pa s at room temperature; the viscosity of liquid water is 10-3 Pa s; and glaciers have a viscosity of 1013–1017 Pa s depending on factors such as temperature, stress and microstructure. At the upper end, Yoshida says that the long-held view, based on rock deformation experiments, is that the viscosity of tectonic plates at the Earth’s surface (where temperatures are relatively low) is 1070 Pa s.
This number is so high that for most purposes, it might as well be infinite, meaning that these plates should behave like rigid bodies. But this accepted wisdom poses a problem: “I realized that I was unable to explain to my students why plates with such high viscosity bend and subduct into the mantle,” Yoshida tells Physics World.
Observed flow and flow parameters
To determine the “effective viscosity” of rock under the temperature and pressure conditions on Earth, Yoshida began by analysing satellite data showing tectonic plate deformations over tens to hundreds of kilometres. Using these data, he could ascertain strain rates – deformations in the plate over a given distance and time – as small as 10-9 per year.
Slow flow: Geodetic observations, laboratory rock-deformation experiments and numerical simulations suggest that there is a geophysically meaningful upper bound of viscosity that marks the transition from deformable flow to effectively rigid behaviour over geological timescales. (Courtesy: Masaki Yoshida/Ritsumeikan University)
By comparing regions under similar stress levels, Yoshida obtained an indication of comparative effective viscosity, which depends on factors such as temperature, composition, grain size, water content, stress state, deformation mechanism and structural heterogeneity. After accounting for assumed stresses, these observations suggested that observed viscosity maxes out at 1028 Pa s.
Yoshida also considered empirical descriptions for the viscosity of various minerals under different types of deformation using parameters from the literature. These yielded a similar upper bound of 1030+/-2 Pa s. Numerical simulations further corroborated this value as a viscosity maximum.
Importance of an upper bound
Taras Gerya, a geodynamicist at ETH Zürich in Switzerland who was not involved in the study, calls Yoshida’s work “an interesting discussion on the significance of viscous deformation for the lithosphere”. However, he notes that, given a realistic stress level of 30 MPa, the maximum viscosity identified gives a cumulative viscous deformation of just 8.5 m for the full 4.5 billion years of Earth’s history. That, he says, is “1000 times smaller than elastic deformation for the same deviatoric stress level”.
While pinning down an exact magnitude for such high viscosities may not greatly change models of deformation, Yoshida thinks that delineating an upper bound may nevertheless improve our understanding of the physical quantities that characterize the behaviour of matter. He also points out that thermal conductivity, which indicates how easily heat is transferred in materials, ranges over only about five orders of magnitude from water to diamond, making it “surprising that viscosity spans a range of about 35 orders of magnitude”.
Yoshida is keen to explore other implications of these results. During the first hundreds of millions of years of Earth’s existence, when it formed and rapidly cooled, he explains that it was covered by a single rigid lid known as the lithosphere. Plate boundaries and motion didn’t emerge until later, approximately 4 billion years ago. “I believe that the question of why plate motion began after the rigid lid formed is closely related to the results of this study,” he says.
Researchers in China have cross-calibrated radiation detectors on 25 navigation satellites. Data from two decades of measurements have been combined to create a record of the flux of relativistic electrons that impinges on Earth’s atmosphere. The technique can be applied to other satellite data, and could boost our understanding of the threat that this radiation poses to satellites and shed light on the solar processes that generate the electron flux.
The Global Positioning System (GPS) uses signals from a constellation of satellites to locate the position of receivers on the Earth’s surface to within several metres. There are currently 32 GPS satellites orbiting about 20,000 km above the Earth and each of them carries a radiation detector. These detectors allow scientists to observe changes in radiation levels in space. Much of this radiation comes in the form of high-energy electrons from the Sun, which can disrupt the operation of satellites and even damage them.
The electron flux rises and falls with the solar cycle. This has a period of about 11 years and involves the waxing and waning of sunspots, solar flares and coronal mass ejections.
For those who design and operate satellites, it is crucial to understand this electron flux. However, it has proven difficult to make full use of the data generated by these detectors because the instruments had not been cross calibrated. Indeed, measurement values of high-energy electrons can vary between satellites by several orders of magnitude when the flux is low. One important issue is that not all satellites use the same detectors – with two different instruments having been deployed.
Cross calibration
Now, researchers in China have done a cross-calibration of the particle detectors on 25 GPS satellites. The result is a calibrated dataset of relativistic-electron flux that spans two complete solar cycles (2000–2020).
To do this, the team looked at two different measurements made by the detectors. One is the differential electron flux at 2 MeV arriving from one specific direction. The other is the integral electron flux electrons arriving from all directions at energies greater than 2 MeV.
Because electron flux is affected by Earth’s magnetic field, the team had to consider its effect on measurements. This was done using a concept called magnetic local time, which accounts for the fact that Earth’s magnetic poles are offset from our planet’s axis of rotation.
The team used a satellite called NS59 as the reference for their study because its detector has produced a consistent set of data from 2004 – overlapping in time all other satellites in the study. By doing several statistical analyses, the team was able incorporate data from 24 of the 25 satellites. One detector, however, remained problematic and the researchers recommend that data from this satellite not be used.
The team says that their technique can now be used to cross-calibrate the detectors at other energies – there are 14 differential and 29 integral channels that can be also be analysed. They have already used the same techniques to cross-calibrate the GPS data with measurements made by satellites in China’s BeiDou positioning system and observations made by NASA’s two Van Allen Probes.
Join us for an in‑depth conversation with Simon Cherry, former editor‑in‑chief of Physics in Medicine & Biology (PMB), as he shares his expert perspective on the evolving landscape of medical physics research, molecular imaging, and non-invasive imaging technologies. Drawing on decades of leadership in biomedical imaging and academic publishing, Simon will reflect on major advances shaping the field, define the characteristics of high‑impact imaging research, and highlight how PMB continues to support rigorous, influential scientific work through its editorial standards and peer‑review practices.
This session will additionally spotlight the research of Xinchen (Alison) Deng, a finalist of the PMB 2024 Early Career Award. Attendees will gain insights into her contributions to the advanced medical imaging community, such as photon-counting CT for clinical applications and how her work supports broader advances in medical physics and X-ray/CT imaging research.
Simon will also discuss what makes early‑career research stand out and share strategies for researchers aiming to increase the visibility, reach, and long‑term impact of their publications within competitive scientific journals.
Left to right: Carol Clark, Simon Cherry, Xinchen (Alison) Deng
Moderator
Carol Clark, Publisher,Physics in Medicine & Biology
Speakers
Simon R Cherry, PhD received his BSc (Hons) in physics with astronomy from University College London in 1986 and a PhD in medical physics from the Institute of Cancer Research, University of London in 1989. Simon is currently Distinguished Research Professor in the Departments of Biomedical Engineering and Radiology at UC Davis and Professor of Total-Body Imaging at King’s College London. Simon’s research interests centre around biomedical imaging. His major contributions have been in developing systems for positron emission tomography (PET), including designing the microPET scanner for small-animal imaging, the earliest examples of simultaneous PET and MRI studies and co-leading the EXPLORER consortium that developed the world’s first total-body PET scanner. Simon is a Fellow of the Royal Society and Member of the U.S. National Academy of Engineering and National Academy of Inventors. He has received several international awards including the Society of Nuclear Medicine and Molecular Imaging Cassen Prize in 2022. He served as editor-in-chief of the journal Physics in Medicine & Biology from 2011–2020. Simon is the author of more than 350 peer-reviewed journal articles, review articles and book chapters in the field of biomedical imaging. He is also lead author of the widely-used textbook Physics in Nuclear Medicine.
Xinchen (Alison) Deng, PhD, is a diagnostic imaging physics resident at The Ohio State University. Her research focuses on advancing photon-counting CT for clinical applications, including multi-contrast imaging, early disease detection, detector optimization, and AI-based improvements in image quality. Before beginning the residency, Xinchen (Alison) was a postdoctoral fellow in medical physics at the University of Victoria, where she worked with Magdalena Bazalova-Carter and collaborated with Redlen Technologies on the optimization of photon-counting detectors and the clinical applications of spectral CT. She received her PhD in medical physics from the University of British Columbia, where she applied Raman spectroscopy, machine learning, and explainable AI to study radiation treatment response in cancer cells and tissues. Her broader research background spans photon-counting CT, spectral X-ray imaging, Raman spectroscopy, radiotherapy response assessment, and AI-driven image and data analysis. Her photon-counting CT research has been featured in the Physics in Medicine & Biology Early Career Researcher Focus Collection. She is a finalist for the PMB Early Career Researcher Award.
About this journal
Physics in Medicine & Biology. The international journal of biomedical physics and engineering, published by IOP Publishing on behalf of the Institute of Physics and Engineering in Medicine (IPEM)
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