Replacing conventional building materials with alternatives that sequester carbon dioxide could allow the world to lock away up to half the CO2 generated by humans each year – about 16 billion tonnes. This is the finding of researchers at the University of California Davis and Stanford University, both in the US, who studied the sequestration potential of materials such as carbonate-based aggregates and biomass fibre in brick.
Despite efforts to reduce greenhouse gas emissions by decarbonizing industry and switching to renewable sources of energy, it is likely that humans will continue to produce significant amounts of CO2 beyond the target “net zero” date of 2050. Carbon storage and sequestration – either at source or directly from the atmosphere – are therefore worth exploring as an additional route towards this goal. Researchers have proposed several possible ways of doing this, including injecting carbon underground or deep under the ocean. However, all these scenarios are challenging to implement practically and pose their own environmental risks.
Modifying common building materials
In the present work, a team of civil engineers and earth systems scientists led by Elisabeth van Roijen (then a PhD student at UC Davis) calculated how much carbon could be stored in modified versions of several common building materials. These include concrete (cement) and asphalt containing carbonate-based aggregates; bio-based plastics; wood; biomass-fibre bricks (from waste biomass); and biochar filler in cement.
The researchers obtained the “16 billion tonnes of CO2” figure by assuming that all aggregates currently employed in concrete would be replaced with carbonate-based versions. They also supplemented 15% of cement with biochar and the remainder with carbonatable cements; increased the amount of wood used in all new construction by 20%; and supplemented 15% of bricks with biomass and the remainder with carbonatable calcium hydroxide. A final element in their calculation was to replace all plastics used in construction today with bio-based plastics and all bitumen with bio-oil in asphalt.
“We calculated the carbon storage potential of each material based on the mass ratio of carbon in each material,” explains van Roijen. “These values were then scaled up based on 2016 consumption values for each material.”
“The sheer magnitude of carbon storage is pretty impressive”
While the production of some replacement materials would need to increase to meet the resulting demand, van Roijen and colleagues found that resources readily available today – for example, mineral-rich waste streams – would already let us replace 10% of conventional aggregates with carbonate-based ones. “These alone could store 1 billion tonnes of CO2,” she says. “The sheer magnitude of carbon storage is pretty impressive, especially when you put it in context of the level of carbon dioxide removal needed to stay below the 1.5 and 2 °C targets set by The Intergovernmental Panel on Climate Change (IPCC).”
Indeed, even if the world doesn’t implement these technologies until 2075, we could still store enough carbon between 2075 and 2100 to stay below these targets, she tells Physics World. “This is assuming, of course, that all other decarbonization efforts outlined in the IPCC reports are also implemented to achieve net-zero emissions,” she says.
Building materials are a good option for carbon storage
The motivation for the study, she explains, came from the urgent need – as expressed by the IPCC – to not only reduce new carbon emissions through rapid and significant decarbonization, but to also remove large amounts of CO2 already present in the atmosphere. “Rather than burying it in geological, terrestrial or ocean reservoirs, we wanted to look into the possibility of leveraging existing technology – namely conventional building materials – as a way to store CO2. Building materials are a good option for carbon storage given the massive quantity (30 billion tonnes) produced each year, not to mention their durability.”
Van Roijen, who is now a postdoctoral researcher at the US Department of Energy Renewable Energy Laboratory, hopes that this work, which is detailed in Science, will go beyond the reach of the research lab and attract the attention of policymakers and industrialists. While some of the technologies outlined in this study are new and require further research, others, such as bio-based plastics, are well established and simply need some economic and political support, she says. “That said, conventional building materials such as concrete and plastics are pretty cheap, so there will need to be some incentive for industries to make the switch over to these low-carbon materials.”
Braille is a tactile writing system that helps people who are blind or partially sighted acquire information by touching patterns of tiny raised dots. Braille uses combinations of six dots (two columns of three) to represent letters, numbers and punctuation. But learning to read braille can be challenging, particularly for those who lose their sight later in life, prompting researchers to create automated braille recognition technologies.
One approach involves simply imaging the dots and using algorithms to extract the required information. This visual method, however, struggles with the small size of braille characters and can be impacted by differing light levels. Another option is tactile sensing; but existing tactile sensors aren’t particularly sensitive, with small pressure variations leading to incorrect readings.
To tackle these limitations, researchers from Beijing Normal University and Shenyang Aerospace University in China have employed an optical fibre ring resonator (FRR) to create a tactile braille recognition system that accurately reads braille in real time.
“Current braille readers often struggle with accuracy and speed, especially when it comes to dynamic reading, where you move your finger across braille dots in real time,” says team leader Zhuo Wang. “I wanted to create something that could read braille more reliably, handle slight variations in pressure and do it quickly. Plus, I saw an opportunity to apply cutting-edge technology – like flexible optical fibres and machine learning – to solve this challenge in a novel way.”
Flexible fibre sensor
At the core of the braille sensor is the optical FRR – a resonant cavity made from a loop of fibre containing circulating laser light. Wang and colleagues created the sensing region by embedding an optical fibre in flexible polymer and connecting it into the FRR ring. Three small polymer protrusions on top of the sensor act as probes to transfer the applied pressure to the optical fibre. Spaced 2.5 mm apart to align with the dot spacing, each protrusion responds to the pressure from one of the three braille dots (or absence of a dot) in a vertical column.
Sensor fabrication The optical FRR is made by connecting ports of a 2×2 fibre coupler to form a loop. The sensing region is then connected into the loop. (Courtesy: Optics Express 10.1364/OE.546873)
As the sensor is scanned over the braille surface, the pressure exerted by the raised dots slightly changes the length and refractive index of the fibre, causing tiny shifts in the frequency of the light travelling through the FRR. The device employs a technique called Pound-Drever-Hall (PDH) demodulation to “lock” onto these shifts, amplify them and convert them into readable data.
“The PDH demodulation curve has an extremely steep linear slope, which means that even a very tiny frequency shift translates into a significant, measurable voltage change,” Wang explains. “As a result, the system can detect even the smallest variations in pressure with remarkable precision. The steep slope significantly enhances the system’s sensitivity and resolution, allowing it to pick up subtle differences in braille dots that might be too small for other sensors to detect.”
The eight possible configurations of three dots generate eight distinct pressure signals, with each braille character defined by two pressure outputs (one per column). Each protrusion has a slightly different hardness level, enabling the sensor to differentiate pressures from each dot. Rather than measuring each dot individually, the sensor reads the overall pressure signal and instantly determines the combination of dots and the character they correspond to.
The researchers note that, in practice, the contact force may vary slightly during the scanning process, resulting in the same dot patterns exhibiting slightly different pressure signals. To combat this, they used neural networks trained on large amounts of experimental data to correctly classify braille patterns, even with small pressure variations.
“This design makes the sensor incredibly efficient,” Wang explains. “It doesn’t just feel the braille, it understands it in real time. As the sensor slides over a braille board, it quickly decodes the patterns and translates them into readable information. This allows the system to identify letters, numbers, punctuation, and even words or poems with remarkable accuracy.”
Stable and accurate
Measurements on the braille sensor revealed that it responds to pressures of up to 3 N, as typically exerted by a finger when touching braille, with an average response time of below 0.1 s, suitable for fast dynamic braille reading. The sensor also exhibited excellent stability under temperature or power fluctuations.
To assess its ability to read braille dots, the team used the sensor to read eight different arrangements of three dots. Using a multilayer perceptron (MLP) neural network, the system effectively distinguished the eight different tactile pressures with a classification accuracy of 98.57%.
Next, the researchers trained a long short-term memory (LSTM) neural network to classify signals generated by five English words. Here, the system demonstrated a classification accuracy of 100%, implying that slight errors in classifying signals in each column will not affect the overall understanding of the braille.
Finally, they used the MLP-LSTM model to read short sentences, either sliding the sensor manually or scanning it electronically to maintain a consistent contact force. In both cases, the sensor accurately recognised the phrases.
The team concludes that the sensor can advance intelligent braille recognition, with further potential in smart medical care and intelligent robotics. The next phase of development will focus on making the sensor more durable, improving the machine learning models and making it scalable.
“Right now, the sensor works well in controlled environments; the next step is to test its use by different people with varying reading styles, or under complex application conditions,” Wang tells Physics World. “We’re also working on making the sensor more affordable so it can be integrated into devices like mobile braille readers or wearables.”
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Written with Los Alamos National Laboratory theoretical physicist Ian Tregillis, who is also a science-fiction author of several books, they have derived a mathematical model of the so-called wild cards virus.
The Wild Cards universe is a series of novels created by a consortium of writers including Martin and Tregillis.
Set largely during an alternate history of the US following the Second World War, the series follows events after an extraterrestrial virus, known as the Wild Card virus, has spread worldwide. It mutates human DNA causing profound changes in human physiology and society at large.
The virus follows a fixed statistical distribution of outcomes in that 90% of those infected die, 9% become physically mutated (referred to as “jokers”) and 1% gain superhuman abilities (known as “aces”). Such capabilities include the ability to fly as well as being able to move between dimensions. The stories in the series then follow the individuals that have been impacted by the virus.
Tregillis and Martin have now derived a formula for the viral behaviour of the Wild Card virus. “Like any physicist, I started with back-of-the-envelope estimates, but then I went off the deep end,” notes Tregillis. “Being a theoretician, I couldn’t help but wonder if a simple underlying model might tidy up the canon.”
The model takes into consideration the severity of the changes (for the 10% that don’t instantly die) and the mix of joke/ace traits. After all, those infected can also become cryto-jokers or crypto-aces – undetected cases where individuals have subtle changes or powers – as well as joker-aces, in which a human develops both mutations and superhuman abilities.
The result is a dynamical system in which a carrier’s state vector constantly evolves through the model space — until their “card” turns. At that point the state vector becomes fixed and its permanent location determines the fate of the carrier. “The time-averaged behavior of this system generates the statistical distribution of outcomes,” adds Tregillis.
The purpose of the paper, and the model, is also to provide an exercise in demonstrating how “whimsical” scenarios can be used to explore concepts in physics and mathematics.
“The fictional virus is really just an excuse to justify the world of Wild Cards, the characters who inhabit it, and the plot lines that spin out from their actions,” says Tregillis.
The exact origins of cosmic phenomena known as fast radio bursts (FRBs) are not fully understood, but scientists at the Massachusetts Institute of Technology (MIT) in the US have identified a fresh clue: at least one of these puzzling cosmic discharges got its start very close to the object that emitted it. This result, which is based on measurements of a fast radio burst called FRB 20221022A, puts to rest a long-standing debate about whether FRBs can escape their emitters’ immediate surroundings. The conclusion: they can.
“Competing theories argued that FRBs might instead be generated much farther away in shock waves that propagate far from the central emitting object,” explains astronomer Kenzie Nimmo of MIT’s Kavli Institute for Astrophysics and Space Research. “Our findings show that, at least for this FRB, the emission can escape the intense plasma near a compact object and still be detected on Earth.”
As their name implies, FRBs are brief, intense bursts of radio waves. The first was detected in 2007, and since then astronomers have spotted thousands of others, including some within our own galaxy. They are believed to originate from cataclysmic processes involving compact celestial objects such as neutron stars, and they typically last a few milliseconds. However, astronomers have recently found evidence for bursts a thousand times shorter, further complicating the question of where they come from.
Nimmo and colleagues say they have now conclusively demonstrated that FRB 20221022A, which was detected by the Canadian Hydrogen Intensity Mapping Experiment (CHIME) in 2022, comes from a region only 10 000 km in size. This, they claim, means it must have originated in the highly magnetized region that surrounds a star: the magnetosphere.
“Fairly intuitive” concept
The researchers obtained their result by measuring the FRB’s scintillation, which Nimmo explains is conceptually similar to the twinkling of stars in the night sky. The reason stars twinkle is that because they are so far away, they appear to us as point sources. This means that their apparent brightness is more affected by the Earth’s atmosphere than is the case for planets and other objects that are closer to us and appear larger.
“We applied this same principle to FRBs using plasma in their host galaxy as the ‘scintillation screen’, analogous to Earth’s atmosphere,” Nimmo tells Physics World. “If the plasma causing the scintillation is close to the FRB source, we can use this to infer the apparent size of the FRB emission region.”
According to Nimmo, different models of FRB origins predict very different sizes for this region. “Emissions originating within the magnetized environments of compact objects (for example, magnetospheres) would produce a much smaller apparent size compared to emission generated in distant shocks propagating far from the central object,” she explains. “By constraining the emission region size through scintillation, we can determine which physical model is more likely to explain the observed FRB.”
Challenge to existing models
The idea for the new study, Nimmo says, stemmed from a conversation with another astronomer, Pawan Kumar of the University of Texas at Austin, early last year. “He shared a theoretical result showing how scintillation could be used a ‘probe’ to constrain the size of the FRB emission region, and, by extension, the FRB emission mechanism,” Nimmo says. “This sparked our interest and we began exploring the FRBs discovered by CHIME to search for observational evidence for this phenomenon.”
The researchers say that their study, which is detailed in Nature, shows that at least some FRBs originate from magnetospheric processes near compact objects such as neutron stars. This finding is a challenge for models of conditions in these extreme environments, they say, because if FRB signals can escape the dense plasma expected to exist near such objects, the plasma may be less opaque than previously assumed. Alternatively, unknown factors may be influencing FRB propagation through these regions.
A diagnostic tool
One advantage of studying FRB 20221022A is that it is relatively conventional in terms of its brightness and the duration of its signal (around 2 milliseconds). It does have one special property, however, as discovered by Nimmo’s colleagues at McGill University in Canada: its light is highly polarized. What is more, the pattern of its polarization implies that its emitter must be rotating in a way that is reminiscent of pulsars, which are highly magnetized, rotating neutron stars. This result is reported in a separate paper in Nature.
In Nimmo’s view, the MIT team’s study of this (mostly) conventional FRB establishes scintillation as a “powerful diagnostic tool” for probing FRB emission mechanisms. “By applying this method to a larger sample of FRBs, which we now plan to investigate, future studies could refine our understanding of their underlying physical processes and the diverse environments they occupy.”
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