A New Approach to Magnetic Field Homogenization

Homogeneous magnetic fields can be generated over relatively large spatial regions through the targeted arrangement of permanent magnets. A well-known example of an effective design is the so-called Halbach array. However, this approach is based on the idealized assumption that very long — ideally infinitely long — magnets (line dipoles) can be arranged in a circle in such a way that the individual contributions superimpose to produce a homogeneous magnetic field in the center region. In practical applications, using magnets of finite length, the resulting field deviates significantly from this ideal: the field strength inside the circle varies considerably depending on the position. The classical Halbach geometry is therefore clearly suboptimal for compact, practically implementable magnet arrangements when the aim is to achieve the strongest and/or most uniform magnetic field possible.

In their work, Peter Blümler and Ingo Rehberg present optimal three-dimensional arrangements of very compact magnets, idealized by point dipoles. With a view to possible applications, they investigated, among other things, the optimal orientation of the magnets for two geometries relevant to practical use: a single ring and a stacked double ring. A so-called “focused” design additionally allows the generation of homogeneous fields outside the magnet plane, for example in an object positioned above the magnets.

For these new arrangements, Rehberg and Blümler developed analytical formulas, which they subsequently validated experimentally. To this end, they constructed magnet arrays from 16 FeNdB cuboids mounted on 3D-printed supports. The resulting magnetic fields were measured and compared with theoretical predictions, revealing excellent agreement. In terms of both magnetic field strength and homogeneity, the new configurations clearly outperform the classical Halbach arrangement as well as its modifications described in the literature.

Potential for Numerous Applications

The new design concepts offer great potential for applications in which strong and homogeneous magnetic fields are required. In conventional magnetic resonance imaging (MRI), for example, powerful superconducting magnets are used to polarize hydrogen nuclei in tissue. These nuclei are then excited by radio waves, generating measurable voltages in detectors surrounding the body. Algorithms use these signals to calculate detailed cross-sectional images that allow physicians to distinguish tissue types based on properties such as density, water or fat content and diffusion. However, superconducting magnets are technically complex and extremely costly, making this technology hardly available in many parts of the world. For such cases, intensive research is underway to develop alternative methods for generating homogeneous magnetic fields using permanent magnets — a field to which the present study makes a promising contribution. Further potential areas of application include particle accelerators and magnetic levitation systems.

An interdisciplinary research team led by Tibbitt has now turned this vision into reality: it has stably incorporated photosynthetic bacteria — known as cyanobacteria — into a printable gel and developed a material that is alive, grows and actively removes carbon from the air. The researchers recently presented their “photosynthetic living material” in a study in the journal Nature Communications.

Key characteristic: Dual carbon sequestration

The material can be shaped using 3D printing and only requires sunlight and artificial seawater with readily available nutrients in addition to CO₂ to grow. “As a building material, it could help to store CO₂ directly in buildings in the future,” says Tibbitt, who co-initiated the research into living materials at ETH Zurich.

The special thing about it: the living material absorbs much more CO₂ than it binds through organic growth. “This is because the material can store carbon not only in biomass, but also in the form of minerals — a special property of these cyanobacteria,” reveals Tibbitt.

Yifan Cui, one of the two lead authors of the study, explains: “Cyanobacteria are among the oldest life forms in the world. They are highly efficient at photosynthesis and can utilize even the weakest light to produce biomass from CO₂ and water.”

At the same time, the bacteria change their chemical environment outside the cell as a result of photosynthesis, so that solid carbonates (such as lime) precipitate. These minerals represent an additional carbon sink and — in contrast to biomass — store CO₂ in a more stable form.

Cyanobacteria as master builders

“We utilize this ability specifically in our material,” says Cui, who is a doctoral student in Tibbitt’s research group. A practical side effect: the minerals are deposited inside the material and reinforce it mechanically. In this way, the cyanobacteria slowly harden the initially soft structures.

Laboratory tests showed that the material continuously binds CO2 over a period of 400 days, most of it in mineral form — around 26 milligrams of CO₂ per gram of material. This is significantly more than many biological approaches and comparable to the chemical mineralization of recycled concrete (around 7 mg CO₂ per gram).

Hydrogel as a habitat

The carrier material that harbours the living cells is a hydrogel — a gel made of cross-linked polymers with a high water content. Tibbitt’s team selected the polymer network so that it can transport light, CO₂, water and nutrients and allows the cells to spread evenly inside without leaving the material.

To ensure that the cyanobacteria live as long as possible and remain efficient, the researchers have also optimised the geometry of the structures using 3D printing processes to increase the surface area, increase light penetration and promote the flow of nutrients.

Co-first author Dalia Dranseike: “In this way, we created structures that enable light penetration and passively distribute nutrient fluid throughout the body by capillary forces.” Thanks to this design, the encapsulated cyanobacteria lived productively for more than a year, the materials researcher in Tibbitt’s team is pleased to report.

Infrastructure as a carbon sink

The researchers see their living material as a low-energy and environmentally friendly approach that can bind CO₂ from the atmosphere and supplement existing chemical processes for carbon sequestration. “In the future, we want to investigate how the material can be used as a coating for building façades to bind CO₂ throughout the entire life cycle of a building,” Tibbitt looks ahead.

There is still a long way to go — but colleagues from the field of architecture have already taken up the concept and realised initial interpretations in an experimental way.

Two installations in Venice and Milan

Thanks to ETH doctoral student Andrea Shin Ling, basic research from the ETH laboratories has made it onto the big stage at the Architecture Biennale in Venice. “It was particularly challenging to scale up the production process from laboratory format to room dimensions,” says the architect and bio-designer, who is also involved in this study.

Ling is doing her doctorate at ETH Professor Benjamin Dillenburger’s Chair of Digital Building Technologies. In her dissertation, she developed a platform for biofabrication that can print living structures containing functional cyanobacteria on an architectural scale.

For the Picoplanktonics installation in the Canada Pavilion, the project team used the printed structures as living building blocks to construct two tree-trunk-like objects, the largest around three metres high. Thanks to the cyanobacteria, these can each bind up to 18 kg of CO₂ per year — about as much as a 20-year-old pine tree in the temperate zone.

“The installation is an experiment — we have adapted the Canada Pavilion so that it provides enough light, humidity and warmth for the cyanobacteria to thrive and then we watch how they behave,” says Ling. This is a commitment: The team monitors and maintains the installation on site — daily. Until November 23.

At the 24th Triennale di Milano, Dafne’s Skin is investigating the potential of living materials for future building envelopes. On a structure covered with wooden shingles, microorganisms form a deep green patina that changes the wood over time: A sign of decay becomes an active design element that binds CO₂ and emphasises the aesthetics of microbial processes. Dafne’s Skin is a collaboration between MAEID Studio and Dalia Dranseike. It is part of the exhibition “We the Bacteria: Notes Toward Biotic Architecture” and runs until November 9.

The photosynthetic living material was created thanks to an interdisciplinary collaboration within the framework of ALIVE (Advanced Engineering with Living Materials). The ETH Zurich initiative promotes collaboration between researchers from different disciplines in order to develop new living materials for a wide range of applications.

In the study, researchers found that the brains of people diagnosed with Down syndrome and Alzheimer’s disease (DSAD) had twice as much iron and more signs of oxidative damage in cell membranes compared to the brains of individuals with Alzheimer’s disease alone or those with neither diagnosis. The results point to a specific cellular death process that is mediated by iron, and the findings may help explain why Alzheimer’s symptoms often appear earlier and more severely in individuals with Down syndrome.

“This is a major clue that helps explain the unique and early changes we see in the brains of people with Down syndrome who develop Alzheimer’s,” said Max Thorwald, lead author of the study and a postdoctoral fellow in the laboratory of University Professor Emeritus Caleb Finch at the USC Leonard Davis School. “We’ve known for a long time that people with Down syndrome are more likely to develop Alzheimer’s disease, but now we’re beginning to understand how increased iron in the brain might be making things worse.”

Down syndrome and Alzheimer’s

Down syndrome is caused by having an extra third copy, or trisomy, of chromosome 21. This chromosome includes the gene for amyloid precursor protein, or APP, which is involved in the production of amyloid-beta (Aβ), the sticky protein that forms telltale plaques in the brains of people with Alzheimer’s disease.

Because people with Down syndrome have three copies of the APP gene instead of two, they tend to produce more of this protein. By the age of 60, about half of all people with Down syndrome show signs of Alzheimer’s disease, which is approximately 20 years earlier than in the general population.

“This makes understanding the biology of Down syndrome incredibly important for Alzheimer’s research,” said Finch, the study’s senior author.

Key findings point to ferroptosis

The research team studied donated brain tissue from individuals with Alzheimer’s, DSAD, and those without either diagnosis. They focused on the prefrontal cortex — an area of the brain involved in thinking, planning, and memory — and made several important discoveries:

• Iron levels much higher in DSAD brains: Compared to the other groups, DSAD brains had twice the amount of iron in the prefrontal cortex. Scientists believe this buildup comes from tiny brain blood vessel leaks called microbleeds, which occur more frequently in DSAD than in Alzheimer’s and are correlated with higher amounts of APP.
• More damage to lipid-rich cell membranes: Cell membranes are made of fatty compounds called lipids and can be easily damaged by chemical stress. In DSAD brains, the team found more byproducts of this type of damage, known as lipid peroxidation, compared to amounts in Alzheimer’s-only or control brains.
• Weakened antioxidant defense systems: The team found that the activity of several key enzymes that protect the brain from oxidative damage and repair cell membranes was lower in DSAD brains, especially in areas of the cell membrane called lipid rafts.

Together, these findings indicate increased ferroptosis, a type of cell death characterized by iron-dependent lipid peroxidation, Thorwald explained: “Essentially, iron builds up, drives the oxidation that damages cell membranes, and overwhelms the cell’s ability to protect itself.”

Lipid rafts: a hotspot for brain changes

The researchers paid close attention to lipid rafts — tiny parts of the brain cell membrane that play crucial roles in cell signaling and regulate how proteins like APP are processed. They found that in DSAD brains, lipid rafts had much more oxidative damage and fewer protective enzymes compared to Alzheimer’s or healthy brains.

Notably, these lipid rafts also showed increased activity of the enzyme β-secretase, which interacts with APP to produce Aβ proteins. The combination of more damage and more Aβ production may promote the growth of amyloid plaques, thus speeding up Alzheimer’s progression in people with Down syndrome, Finch explained.

Rare Down syndrome variants offer insight

The researchers also studied rare cases of individuals with “mosaic” or “partial” Down syndrome, in which the third copy of chromosome 21 is only present in a smaller subset of the body’s cells. These individuals had lower levels of APP and iron in their brains and tended to live longer. In contrast, people with full trisomy 21 and DSAD had shorter lifespans and higher levels of brain damage.

“These cases really support the idea that the amount of APP — and the iron that comes with it — matters a lot in how the disease progresses,” Finch said.

Looking ahead

The team says their findings could help guide future treatments, especially for people with Down syndrome who are at high risk of Alzheimer’s. Early research in mice suggests that iron-chelating treatments, in which medicine binds to the metal ions and allows them to leave the body, may reduce indicators of Alzheimer’s pathology, Thorwald noted.

“Medications that remove iron from the brain or help strengthen antioxidant systems might offer new hope,” Thorwald said. “We’re now seeing how important it is to treat not just the amyloid plaques themselves but also the factors that may be hastening the development of those plaques.”

The study was supported by the National Institute on Aging, National Institutes of Health (P30-AG066519, R01-AG051521, P50-AG05142, P01-AG055367, R01AG079806, P50-AG005142, P30-AG066530, P30-AG066509, U01-AG006781, T32AG052374, R01AG079806-02S1, and T32-AG000037); Cure Alzheimer’s Fund; Simons Collaboration on Plasticity in the Aging Brain (SF811217); Larry L. Hillblom Foundation (2022-A-010-SUP); Glenn Foundation for Medical Research; and the Navigage Foundation Award.

Published in the journal Nature Communications, the study reveals previously unrecognized rooting patterns, altering our understanding of how ecosystems

respond to changing environmental conditions. More importantly, the study suggests that plants might transport and store fixed carbon deeper than currently thought — welcome news at a time when CO2 levels are at an 800,000-year high, according to the World Meteorological Organization’s “State of the Global Climate Report” issued in March.

“Understanding where plants grow roots is vital, as deeper roots could mean safer and longer-term carbon storage. Harsher conditions at depth may prevent detritus-feeding microbes from releasing carbon back to the atmosphere,” says Mingzhen Lu, an assistant professor at New York University’s Department of Environmental Studies and the paper’s lead author. “Our current ecological observations and models typically stop at shallow depths; by not looking deep enough, we may have overlooked a natural carbon storage mechanism deep underground.”

The research team used data from the National Ecological Observatory Network (NEON) to examine rooting depth. The NEON database includes samples collected from soil 6.5 feet below the surface, far deeper than the one-foot depth of traditional ecological studies. This unprecedented depth allowed researchers to detect additional root patterns, spanning diverse climate zones and ecosystem types from the Alaskan tundra to Puerto Rico’s rainforests.

The scientists’ work focused on three questions — all with the aim of better understanding plants’ resource acquisition strategies and their resilience in response to environmental change:

• How does the abundance of roots change with depth?
• What are the factors that impact the distribution of roots with depth?
• Are nutrients in deeper soils equally, under-, or over-exploited by fine roots compared with surface soil?

The researchers found that nearly 20 percent of the studied ecosystems had roots that peaked twice across depth — a phenomenon called “bimodality.” In these cases, plants developed a second, deeper layer of roots, often more than three feet underground and aligning with nutrient-rich soil layers.This suggests that plants grew — in previously unknown ways — to exploit additional sustenance.

“The current understanding of roots is literally too shallow. Above ground, we have eagle vision — thanks to satellites and remote sensing. But below ground, we have mole vision,” observes Lu, former Omidyar Fellow who conducted part of this research at the Sante Fe Institute and as a postdoctoral affiliate at Stanford University. “Our limited below ground vision means that we cannot estimate the full ability of plants to store carbon deep in the soil.”

“Deep plant roots may cause increased soil carbon storage in one condition or lead to losses in other conditions due to a stimulation of soil microbes,” suggests coauthor Avni Malhotra, the lead author of a companion study that investigated the connection between root distribution and soil carbon stock. “This discovery opens a new avenue of inquiry into how bimodal rooting patterns impact the dynamics of nutrient flow, water cycling, and the long-term capacity of soils to store carbon.”

“Scientists and policymakers need to look deeper beneath the Earth’s surface as these overlooked deep soil layers may hold critical keys for understanding and managing ecosystems in a rapidly changing climate,” concludes Lu. “The good news is plants may already be naturally mitigating climate change more actively than we’ve realized — we just need to dig deeper to fully understand their potential.”

The study also included researchers from Boston College, Columbia University, Dartmouth College, the Morton Arboretum, the National Ecological Observatory Network-Battelle, Pacific Northwest National Laboratory, and Stanford University.

Scientists used satellite data, drones and on-the-ground observations to assess the edges of existing peatlands (waterlogged ecosystems that store vast amounts of carbon).

The study – led by the University of Exeter – found peatlands in the European and Canadian Arctic have expanded outwards in the last 40 years.

While this could slow climate change by storing carbon, the researchers warn that extreme future warming could cause widespread loss of peatlands – releasing that carbon and further accelerating the climate crisis.

“The Arctic has warmed faster than the rest of the planet, with average temperatures increasing by about 4°C in the last four decades,” said Dr Katherine Crichton.

“This has improved growing conditions for plants, causing ‘greening’ of the Arctic. We wanted to identify if this greening could be from peatland plant communities.

“We know from paleo records that warmer periods in Earth’s history led to more carbon being stored in peatlands.

“Our new study puts these pieces together to examine whether our warming climate is causing peatland expansion – and we find strong evidence that it is.”

Peatlands cover just 3% of Earth’s surface but they store about 600 billion tons of carbon – more than all the world’s forest biomass combined.

The Arctic has large peatland areas but these peter out in the far north, where harsh conditions limit plant growth.

In the new study, researchers examined 16 sites – a range of peatlands in both the low and high Arctic – and compared data from 1985-95 with the last 15-20 years.

They found strong evidence of expansion at more than two thirds of sites (measured by “peak-summer greening” – increased growth of peatland-forming plants at the edges of existing peatlands).

The largest changes were found in places with the highest increases in summer temperature, such as the Norwegian islands of Svalbard.

“Our findings suggest Arctic peatlands are an increasingly important natural carbon sink, at least in the near term,” said Professor Karen Anderson, from the Environment and Sustainability Institute on Exeter’s Penryn Campus in Cornwall.

“But if temperatures continue to rise, we are likely to see changes in rainfall, and we are not sure how sustainable new or existing peatlands will be. Plus we could see increases of methane emissions at the same time.

“So – while our study gives us some positive news – it does not detract from the urgent need to reduce greenhouse gas emissions and stabilize our climate.”

The story behind the study

This study took researchers on an unexpected journey that included COVID lockdowns, polar bear safety training and dragging a canoe overland.

Like many research projects, it started with pilot studies – one extracting and analyzing peatland samples in Canada and Finland, the other testing “remote sensing” with drones and satellites.

The team wanted to combine these to find out how climate change is affecting Arctic peatlands. They started applying for funding in 2013, and got their first rejection in 2015. Two more rejections came the following year. In 2018, they finally got a grant – and the project started in summer 2019.

Dr Crichton used Google Earth Engine to identify possible study sites, and Professor Angela Gallego-Sala went on the first fieldwork expedition – to Svalbard, where she received training on avoiding encounters with hungry polar bears.

With the research finally making progress, COVID lockdowns halted fieldwork and lab work. While this hampered the project, Dr Crichton’s computer-based work could continue. “I was still at my desk using Google Earth Engine,” she said. “Lockdown didn’t make any difference to the work I was doing.”

So Dr Crichton continued identifying fieldwork sites, analyzing data and applying for permits – paving the way for fieldwork in Canada in 2021-22. On one of those expeditions, Professor Gallego-Sala stayed at a basic research station on Bylot Island where the washing facility was a “half-frozen lake.” She said: “It was light all the time. You could do fieldwork all day long and all night if you wanted to.”

From that research station, the team visited remote sites via helicopter. Many sites had no name, and the pilot wanted names in order to arrange pick-ups – so sites got informal names including “Glacial Nirvana” and “Angela’s Paradise.” At each site, the team extracted peatland cores to learn about the history of the peatland and how it might be changing.

At Salluit in northern Canada, the team had an Inuit guide for expeditions out into the peatland – during which they saw wildlife including black bears and reindeer, and caught fish and mussels for dinner each evening. When the team laid out their plan one day, the guide shrugged and said: “You can go wherever you want.” He did not mention that their plan would leave their canoe stuck on a large area of sand at low tide.

The three female researchers had to push the stranded boat overland, while the guide sat in it. “We pushed it a long way through the sand,” Professor Gallego-Sala said. “It was pretty tough – but it was also hilarious, and we managed to get it out.”

“Meanwhile, I’m still sat at my computer by the way,” said Dr Crichton, laughing. But this work provided a crucial component – allowing comparison between peatland cores and long-term satellite data that shows peatland edges getting greener as vegetation spreads.

Professor Gallego-Sala added: “Going out for fieldwork is a short time in comparison to the rest of the work. There is lots of lab work to analyse the samples, then extensive data analysis before the findings can be written into a published paper.”

The study is part of a project called Increased Accumulation in Arctic Peatlands (ICAAP), funded by the Natural Environment Research Council.

The paper, published in the journal Communications Earth and Environment, is entitled: “Satellite data indicates recent Arctic peatland expansion with warming.”