̽��ֱ�� of Cambridge - magnetism

Swarming cicadas, stock traders, and the wisdom of the crowd

sc604 — Thu, 01 Feb 2024 14:36:51 +0000

Pick almost any location in the eastern United States – say, Columbus Ohio. Every 13 or 17 years, as the soil warms in springtime, vast swarms of cicadas emerge from their underground burrows singing their deafening song, take flight and mate, producing offspring for the next cycle.

This noisy phenomenon repeats all over the eastern and southeastern US as 17 distinct broods emerge in staggered years. In spring 2024, billions of cicadas are expected as two different broods – one that appears every 13 years and another that appears every 17 years – emerge simultaneously.

Previous research has suggested that cicadas emerge once the soil temperature reaches 18°C, but even within a small geographical area, differences in sun exposure, foliage cover or humidity can lead to variations in temperature.

Now, in a paper published in the journal Physical Review E, researchers from the ̽��ֱ�� of Cambridge have discovered how such synchronous cicada swarms can emerge despite these temperature differences.

̽��ֱ��researchers developed a mathematical model for decision-making in an environment with variations in temperature and found that communication between cicada nymphs allows the group to come to a consensus about the local average temperature that then leads to large-scale swarms. ̽��ֱ��model is closely related to one that has been used to describe ‘avalanches’ in decision-making like those among stock market traders, leading to crashes.

Mathematicians have been captivated by the appearance of 17- and 13-year cycles in various species of cicadas, and have previously developed mathematical models that showed how the appearance of such large prime numbers is a consequence of evolutionary pressures to avoid predation. However, the mechanism by which swarms emerge coherently in a given year has not been understood.

In developing their model, the Cambridge team was inspired by previous research on decision-making that represents each member of a group by a ‘spin’ like that in a magnet, but instead of pointing up or down, the two states represent the decision to ‘remain’ or ‘emerge’.

̽��ֱ��local temperature experienced by the cicadas is then like a magnetic field that tends to align the spins and varies slowly from place to place on the scale of hundreds of metres, from sunny hilltops to shaded valleys in a forest. Communication between nearby nymphs is represented by an interaction between the spins that leads to local agreement of neighbours.

̽��ֱ��researchers showed that in the presence of such interactions the swarms are large and space-filling, involving every member of the population in a range of local temperature environments, unlike the case without communication in which every nymph is on its own, responding to every subtle variation in microclimate.

̽��ֱ��research was carried out Professor Raymond E Goldstein, the Alan Turing Professor of Complex Physical Systems in the Department of Applied Mathematics and Theoretical Physics (DAMTP), Professor Robert L Jack of DAMTP and the Yusuf Hamied Department of Chemistry, and Dr Adriana I Pesci, a Senior Research Associate in DAMTP.

“As an applied mathematician, there is nothing more interesting than finding a model capable of explaining the behaviour of living beings, even in the simplest of cases,” said Pesci.

̽��ֱ��researchers say that while their model does not require any particular means of communication between underground nymphs, acoustical signalling is a likely candidate, given the ear-splitting sounds that the swarms make once they emerge from underground.

̽��ֱ��researchers hope that their conjecture regarding the role of communication will stimulate field research to test the hypothesis.

“If our conjecture that communication between nymphs plays a role in swarm emergence is confirmed, it would provide a striking example of how Darwinian evolution can act for the benefit of the group, not just the individual,” said Goldstein.

This work was supported in part by the Complex Physical Systems Fund.

Reference:
R E Goldstein, R L Jack, and A I Pesci. ‘How Cicadas Emerge Together: Thermophysical Aspects of their Collective Decision-Making.’ Physical Review E (2024). DOI: 10.1103/PhysRevE.109.L022401

̽��ֱ��springtime emergence of vast swarms of cicadas can be explained by a mathematical model of collective decision-making with similarities to models describing stock market crashes.

Ed Reschke via Getty Images

Adult Periodical Cicada

̽��ֱ��text in this work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License. Images, including our videos, are Copyright © ̽��ֱ�� of Cambridge and licensors/contributors as identified. All rights reserved. We make our image and video content available in a number of ways – on our main website under its Terms and conditions, and on a range of channels including social media that permit your use and sharing of our content under their respective Terms.

Yes

Diamonds and rust help unveil ‘impossible’ quasi-particles

sc604 — Tue, 05 Dec 2023 10:02:43 +0000

Researchers led by the ̽��ֱ�� of Cambridge used a technique known as diamond quantum sensing to observe swirling textures and faint magnetic signals on the surface of hematite, a type of iron oxide.

̽��ֱ��researchers observed that magnetic monopoles in hematite emerge through the collective behaviour of many spins (the angular momentum of a particle). These monopoles glide across the swirling textures on the surface of the hematite, like tiny hockey pucks of magnetic charge. This is the first time that naturally occurring emergent monopoles have been observed experimentally.

̽��ֱ��research has also shown the direct connection between the previously hidden swirling textures and the magnetic charges of materials like hematite, as if there is a secret code linking them together. ̽��ֱ��results, which could be useful in enabling next-generation logic and memory applications, are reported in the journal Nature Materials.

According to the equations of James Clerk Maxwell, a giant of Cambridge physics, magnetic objects, whether a fridge magnet or the Earth itself, must always exist as a pair of magnetic poles that cannot be isolated.

“ ̽��ֱ��magnets we use every day have two poles: north and south,” said Professor Mete Atatüre, who led the research. “In the 19th century, it was hypothesised that monopoles could exist. But in one of his foundational equations for the study of electromagnetism, James Clerk Maxwell disagreed.”

Atatüre is Head of Cambridge’s Cavendish Laboratory, a position once held by Maxwell himself. “If monopoles did exist, and we were able to isolate them, it would be like finding a missing puzzle piece that was assumed to be lost,” he said.

About 15 years ago, scientists suggested how monopoles could exist in a magnetic material. This theoretical result relied on the extreme separation of north and south poles so that locally each pole appeared isolated in an exotic material called spin ice.

However, there is an alternative strategy to find monopoles, involving the concept of emergence. ̽��ֱ��idea of emergence is the combination of many physical entities can give rise to properties that are either more than or different to the sum of their parts.

Working with colleagues from the ̽��ֱ�� of Oxford and the National ̽��ֱ�� of Singapore, the Cambridge researchers used emergence to uncover monopoles spread over two-dimensional space, gliding across the swirling textures on the surface of a magnetic material.

̽��ֱ��swirling topological textures are found in two main types of materials: ferromagnets and antiferromagnets. Of the two, antiferromagnets are more stable than ferromagnets, but they are more difficult to study, as they don’t have a strong magnetic signature.

To study the behaviour of antiferromagnets, Atatüre and his colleagues use an imaging technique known as diamond quantum magnetometry. This technique uses a single spin – the inherent angular momentum of an electron – in a diamond needle to precisely measure the magnetic field on the surface of a material, without affecting its behaviour.

For the current study, the researchers used the technique to look at hematite, an antiferromagnetic iron oxide material. To their surprise, they found hidden patterns of magnetic charges within hematite, including monopoles, dipoles and quadrupoles.

“Monopoles had been predicted theoretically, but this is the first time we’ve actually seen a two-dimensional monopole in a naturally occurring magnet,” said co-author Professor Paolo Radaelli, from the ̽��ֱ�� of Oxford.

“These monopoles are a collective state of many spins that twirl around a singularity rather than a single fixed particle, so they emerge through many-body interactions. ̽��ֱ��result is a tiny, localised stable particle with diverging magnetic field coming out of it,” said co-first author Dr Hariom Jani, from the ̽��ֱ�� of Oxford.

“We’ve shown how diamond quantum magnetometry could be used to unravel the mysterious behaviour of magnetism in two-dimensional quantum materials, which could open up new fields of study in this area,” said co-first author Dr Anthony Tan, from the Cavendish Laboratory. “ ̽��ֱ��challenge has always been direct imaging of these textures in antiferromagnets due to their weaker magnetic pull, but now we’re able to do so, with a nice combination of diamonds and rust.”

̽��ֱ��study not only highlights the potential of diamond quantum magnetometry but also underscores its capacity to uncover and investigate hidden magnetic phenomena in quantum materials. If controlled, these swirling textures dressed in magnetic charges could power super-fast and energy-efficient computer memory logic.

̽��ֱ��research was supported in part by the Royal Society, the Sir Henry Royce Institute, the European Union, and the Engineering and Physical Sciences Research Council (EPSRC), part of UK Research and Innovation (UKRI).

Reference:
K C Tan, Hariom Jani, Michael Högen et al. ‘Revealing Emergent Magnetic Charge in an Antiferromagnet with Diamond Quantum Magnetometry.’ Nature Materials (2023). DOI: 10.1038/s41563-023-01737-4.

For more information on energy-related research in Cambridge, please visit the Energy IRC, which brings together Cambridge’s research knowledge and expertise, in collaboration with global partners, to create solutions for a sustainable and resilient energy landscape for generations to come.

Researchers have discovered magnetic monopoles – isolated magnetic charges – in a material closely related to rust, a result that could be used to power greener and faster computing technologies.

If monopoles did exist, and we were able to isolate them, it would be like finding a missing puzzle piece that was assumed to be lost

Mete Atatüre

Anthony Tan and Michael Hoegen

Magnetic monopoles in hematite

̽��ֱ��text in this work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License. Images, including our videos, are Copyright © ̽��ֱ�� of Cambridge and licensors/contributors as identified. All rights reserved. We make our image and video content available in a number of ways – as here, on our main website under its Terms and conditions, and on a range of channels including social media that permit your use and sharing of our content under their respective Terms.

Yes

Roadside hedges can reduce harmful ultrafine particle pollution around schools

cmm201 — Wed, 13 Sep 2023 14:19:33 +0000

̽��ֱ��research, a collaboration with Lancaster ̽��ֱ��, found that hedges can act as protective barriers against air pollution from major city roads by soaking up significant quantities of harmful particles emitted by traffic.

̽��ֱ��researchers applied a new type of pollution analysis, using magnetism to study particles trapped by a hedge separating a major 6-lane road from a primary school in Manchester, UK. They found that the hedge was especially successful in removing ultrafine particle pollution, which can be more damaging to health.

“Our findings show that hedges can provide a simple, cheap and effective way to help reduce exposure to local sources of pollution,” said lead author Hassan Sheikh from Cambridge’s Department of Earth Sciences.

̽��ֱ��new study differs from conventional air pollution studies because the researchers specifically measured magnetic particles, which originate from vehicle exhaust and the wearing of brake pads and tyres. That allowed them to distinguish local traffic pollution from other sources of air pollution.

In England alone, epidemiological studies estimate that 26,000 to 38,000 deaths and thousands of NHS hospital admissions are linked to dust-like particles carried in air pollution — much of which is generated by heavy traffic in urban environments.

This particle pollution — or particulate matter — is made up of a variety of chemical compounds, metals and other materials, some of which are toxic. ̽��ֱ��bigger particles (which are still tiny) measure less than 10 microns in diameter (called PM10) and are easily inhaled. Finer particles of less than 2.5 microns across (PM2.5) can penetrate deeper into the lungs and are small enough to enter the bloodstream.

Children attending schools next to busy roads are especially vulnerable to the effects of air pollution because their airways are still developing and they breath faster than adults.

Sheikh and the team studied magnetic particles captured by a western red cedar ‘tredge’ (trees managed at head-height), which was previously installed outside St Ambrose Primary School as part of a trial led by Lancaster ̽��ֱ��.

“Western red cedar does a great job in 'capturing ' particulate pollution because it has abundant, fine, evergreen leaves into which airborne particles bump and then settle from the roadside air,” said study co-author Professor Barbara Maher from the Lancaster ̽��ֱ��, who led the previous research.

Sheikh and the team measured particles of varying sizes on the leaves of the tredge and used air filters to measure particle abundance at intervals downwind toward the school playground.

They also developed a new experiment that used a tracer gas to understand how ultrafine particles (measuring less that 2.5 microns) moved through and were trapped by the tredge.

Their results revealed that there was a substantial reduction in particle pollution downwind of the tredge. “ ̽��ֱ��tredge acts as a permeable barrier, intercepting and capturing particles effectively on its leaves,” said Sheikh.

In the school playground, 30 metres from the road, they measured a 78% decrease in PM10 relative to roadside air.

They noticed that this removal was even more efficient for ultrafine PM2.5 particles. “What was remarkable was just how efficiently the tredge hoovered up the very finest particles,” said senior author Professor Richard Harrison, also from Cambridge’s Department of Earth Sciences. They measured an 80% reduction in the ultrafine particles just behind the tredge.

They think the ultrafine particles are preferentially filtered out by the tredge because they have a higher likelihood of being captured on the ridged surfaces of the red cedar leaves than coarser particles.

However, they did note a slight uptick in levels of magnetic PM2.5 in the playground, although they were still 63% below roadside air. “ ̽��ֱ��ultrafine particles were very effectively removed, but this shows that some air still goes over or around the tredge,” said Sheikh. Less is currently known about how particulate matter moves and disperses at this higher level, where air mixes around buildings and trees.

“That means the design and placement of tredges near playgrounds and schools should be carefully considered so that their ability to soak up particles can be used to maximum effect,” said Harrison.

Cllr Tracey Rawlins, Executive Member for Environment for Manchester City Council, said: "We were keen to be part of this study as Manchester seeks to embrace innovation in our efforts to become a greener city with cleaner air and tackle climate change.

" ̽��ֱ��findings underline the contribution which nature-based innovations can make to rising to that challenge. We look forward to delivering more green screens as well as many trees at school sites, complementing our education climate change strategy," said Rawlins.

Previously, Sheikh and Harrison used their new magnetic analysis to identify high levels of ultrafine particles polluting the London Underground. They now plan on working with colleagues at the MRC Toxicology Unit in Cambridge to find out what happens when cells are exposed to this type of ultrafine particle pollution.

Reference

Sheikh, H A, Maher, B A, Woods, A W, Tung, P Y, and Harrison, R J (2023). Efficacy of green infrastructure in reducing exposure to local, traffic-related sources of airborne particulate matter (PM). Science of the Total Environment, 166598.

A new study led by Cambridge ̽��ֱ�� confirms that planting hedges between roadsides and school playgrounds can dramatically reduce children’s exposure to traffic-related particle pollution.

Our findings show that hedges can provide a simple, cheap and effective way to help reduce exposure to local sources of pollution

Hassan Sheikh

H A Sheikh

Monitoring particle air pollution either side of the tredge installed at St Ambrose primary school, Manchester

̽��ֱ��text in this work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License. Images, including our videos, are Copyright © ̽��ֱ�� of Cambridge and licensors/contributors as identified. All rights reserved. We make our image and video content available in a number of ways – as here, on our main website under its Terms and conditions, and on a range of channels including social media that permit your use and sharing of our content under their respective Terms.

Yes

London Underground polluted with metallic particles small enough to enter human bloodstrem

sc604 — Thu, 15 Dec 2022 15:55:12 +0000

̽��ֱ��London Underground is polluted with ultrafine metallic particles small enough to end up in the human bloodstream, according to ̽��ֱ�� of Cambridge researchers. These particles are so small that they are likely being underestimated in surveys of pollution in the world’s oldest metro system.