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Physics in the pandemic: ‘Our mission was to include young nuclear physicists wherever they were in the world’

Cebo Ngwetsheni2
Online success: Cebo Ngwetsheni, a PhD student from the University of the Western Cape, receives an award at the 10th anniversary “Tastes of nuclear physics” conference for a paper in Physics Letters B (Courtesy: David Jenkins)

We all remember the pictures of the famous Solvay conferences in the 1910s and 1920s, where the foundations of the “new physics” and quantum mechanics were discussed. A group of distinguished, wing-collared and moustachioed Edwardian gentlemen admits a single interloper in the form of Marie Curie. It was all a very different age.

But are our present-day conferences really more diverse? At first glance, they seem to be, as advisory committees challenge themselves to support diversity and gender inclusion.

However, we often choose to ignore the barriers to involvement of participants: those whose family situation does not allow them to travel, those who are uncomfortable to travel because of hostility to difference in the host country particularly attitudes to gender, race, homosexuality or disability.

A bigger issue still is the difficulty in including those who don’t have the resources to travel. Some conferences offer bursaries but nowhere near the levels needed to include large numbers of participants from developing countries.

If 2020 has taught us anything, it’s that our ability to communicate across the planet and talk “face-to-face” is limited only by our internet bandwidth.

We exacerbate this issue by holding conferences at which the main event is, in practice, a skiing holiday, or beach holiday, or safari excursion with conference talks pushed to the margins to facilitate freeing up the day for leisure. Many see their involvement in such conferences as “a perk of the job”.

If 2020 has taught us anything, it’s that our ability to communicate across the planet and talk “face-to-face” is limited only by our internet bandwidth. Recently, I was privileged to be part of an online conference that promises to change how we view such events forever.

Entitled “Tastes of nuclear physics”, it is one that I have supported for some years. It began 10 years ago at the University of Western Cape (UWC) – a historically-disadvantaged university in South Africa.

Its driving force is Nico Orce, who initially devised the “Tastes of nuclear physics” as a way of bringing foreign visitors to UWC to teach students on their MaNuS (Masters of nuclear science) programme about nuclear physics in a “summer school” format.

Since then, the event has grown and grown. Last year, it travelled 2000 km to the University of Zululand and hundreds of undergraduate students there also attended and heard speakers not only on the state-of-the-art but inspiring speakers who talked about their own careers and surmounting the challenges they had felt growing up in South Africa.

This year, we had to go online but we made it our mission to include any young people working in nuclear physics wherever they were in the world.

I feel it is no exaggeration to say that this year’s tenth anniversary “Tastes” on-line on Zoom was a historic event. The technology actually worked: the first speaker was in Australia, the chair was in the UK and the first question came from a scientist in India.

The sessions were punctuated with videos of the UWC choir singing that made you want to get up from the Zoom slump and jig about.

Students from all over the world joined including from Lebanon, India and, of course, South Africa. They asked questions and interacted with the speakers in virtual coffee breaks. We also recorded the lectures and rebroadcast them on YouTube for those with poor internet connections.

The diversity of the participants and speakers was impressive. We had talks from South African scientists on their own work in nuclear physics, the application of nuclear-physics technology to improving diamond mining, and again, saw role models speak about their careers.

The sessions were punctuated with videos of the UWC choir singing and renditions of “Gimme hope Jo’anna” and other music that made you want to get up from the Zoom slump and jig about.

Parts of the conference were moving and inspirational, particularly the “Women in science” session and the award of prizes from sponsors to some MaNuS students for publications they had lead.

We heard, for example, of one student, an orphan, whose sister had sat selling vegetables on the side of the road to pay for his university studies. I was left feeling at the end of the conference, as I have at many points in this turbulent year, that some things had significantly changed.

We all miss conferences where we can meet face-to-face but, as we hopefully return to something more like normality in 2021, let’s see how we can retain benefits for the many and not for the privileged few.

Silicon qubits find the right position

Two-qubit gates – the central building blocks of quantum computers – operate by exploiting tunnelling interactions between qubits. A team of researchers in Australia has now found a way to optimize these interactions in silicon by determining where the qubits should be positioned within the silicon crystal lattice. The work, which was carried out at the Centre of Excellence for Quantum Computation and Communication Technology (CQC2T) and Silicon Quantum Computing (SQC), is a step forward in the race to scale up silicon-based quantum processors.

Quantum tunnelling occurs when a particle passes through an energy barrier despite not having enough energy (according to classical physics) to overcome it. The phenomenon is at the heart of many modern technologies, including scanning tunnelling microscopy (STM), some types of CMOS electronics and quantum devices in which electrons are confined and manipulated.

Creating robust interactions between qubits

In 2018, the CQC2T/SQC team, led by Michelle Simmons of UNSW Sydney, used STM lithography to create qubits from phosphorus donor atoms in a silicon crystal. This technique makes it possible to position the atoms anywhere in a single atomic plane of the crystal. By placing phosphorus atoms a few nanometres from each other, the team created 2D donor arrays in which direct tunnelling interactions take precedence over dipolar (Coulomb) coupling. In this previous work, the researchers were able to map out the atoms’ wavefunction in 2D STM images and identify their exact spatial location.

In the new work, led this time by Sven Rogge, the researchers used STM to observe atomic-scale details of the interactions between coupled atom qubits. They also determined both the anisotropy in the wavefunction and the interference between the atoms directly in the plane. From this, the researchers learned that the positions of the qubits in the silicon lattice strongly affect the robustness of their interactions. In particular, they found that there is a special angle within the [110] plane of the silicon crystal in which these interactions are the most resilient. Such strong interactions are essential for making multi-qubit processors and, ultimately, a useful quantum computer.

Towards larger-scale processors

The advance in qubit positioning came about via a collaboration with researchers at the University of Melbourne. “Our colleagues at UNSW Sydney were able to obtain atomic-resolution images of coupled electron wave functions while we conducted advanced theoretical simulations to analyse these images and map the two-qubit interactions,” says CQC²T Deputy Director Lloyd Hollenberg, who led the Melbourne team. “We can use our previously-developed STM lithography technique to precisely place the phosphorus atoms at the special angle we discovered, so atom-based qubit devices could immediately benefit from the new result.”

The work, which is reported in Nature Communications, follows on from experiments done by the team in 2019 in which they used their precision placement approach to build the fastest two-qubit gate in silicon to date. The latest findings will allow for larger-scale processors, the researchers say.

The team is now working on building the first useful commercial quantum computer in silicon. “Since our results directly link to the STM lithography technique pioneered at UNSW, we hope to demonstrate enhanced device performance and reliability of multi-qubit devices fairly quickly,” study lead author Benoit Voisin tells Physics World. “We would also like to scale up our imaging technique to explore complex many-body regimes. For instance, strong tunnelling Coulomb couplings can be achieved at very short inter-dopant distances – a regime thought to be linked to high-temperature superconductivity.”

Video summary of the Physics World 2020 Breakthrough of the Year

The Physics World 2020 Breakthrough of the Year has been awarded to an international team for creating a silicon-based material with a direct band gap that emits light at wavelengths used for optical telecommunications. This video provides a brief overview of the research and the applications it might enable in the coming years.

The highs and lows of physics in 2020, we reveal our Breakthrough of the Year

While 2020 started like any other year, it quickly became apparent that it was going to be a year like no other. In this episode of the Physics World Weekly podcast, we have a lively chat about how the extraordinary events of 2020 affected physics and physicists, and how scientists around the world have rallied to fight COVID-19.

Also in this episode is an interview with Erik Bakkers of the Eindhoven University of Technology in the Netherlands, whose team has won the Physics World 2020 Breakthrough of the Year.

This is the final Physics World Weekly podcast of 2020. Please join us again next year on 7 January for the next episode.

Silicon-based material with a direct band gap is the Physics World 2020 Breakthrough of the Year

It is no exaggeration to say that finding a silicon-based material that emits useful light has been the Holy Grail of optoelectronics. Normally, silicon has an indirect electronic band gap, which means that it does not emit light. As a result, silicon must be integrated with other direct-band-gap semiconductor materials to create the optoelectronic devices that supply the pulses of light that drive information on the Internet. While this integration is possible, it is difficult and expensive.

To create a direct band gap, Bakkers and colleagues had to find a way of growing crystals of silicon-germanium alloy with a hexagonal crystal structure, rather than the usual diamond-like structure. They did this by creating nanowires of the alloy, which emitted infrared light. As well as having applications in optical telecoms and optical computing, the new silicon-based material could be used to create chemical sensors.

Interview with Erik Bakkers
Interview with Erik Bakkers

However, as Bakkers points out in the above audio interview, there is more work to be done before the material can be used in practical devices. In particular, the team will have to work out how to get the material to grow on flat surfaces, rather than as nanowires, so that it can be used in large-scale semiconductor processing.

Bakkers expects that the team will soon be able to create a silicon-based laser. Ultimately, he hopes that the material could be used to fabricate lasers on a chip that can create optical signals. Other components that are needed to convert optical signals into electronic signals and vice versa could also be made, including optical amplifiers and detectors.

Indeed, the breakthrough could lead to a new world of opportunities for silicon devices.

The Breakthrough of the Year and the nine runners-up are selected by five Physics World editors, who have sifted through hundreds of research updates published on the website this year. In addition to having been reported in Physics World in 2020, our selections must meet the following criteria:

  • Significant advance in knowledge or understanding
  • Importance of work for scientific progress and/or development of real-world applications
  • Of general interest to Physics World readers

Here are the nine runners-up that make up the rest of the Physics World Top 10 Breakthroughs for 2020.

Taking snapshots of a quantum measurement

To Markus Hennrich and colleagues at Stockholm University, Sweden, together with researchers at the universities of Siegen in Germany and the Basque Country and Seville in Spain, for using a series of “weak” measurements (the subject of Physics World’s 2011 Breakthrough of the Year) to probe the nature of superposition collapse in quantum mechanics. While the act of measurement usually forces quantum systems into definite classical states, the work of Hennrich and colleagues showed that some measurements don’t destroy all quantum information. By taking a series of “snapshots” during experiments on a single ion of strontium, the team revealed that measurements are not instantaneous, but instead gradually convert superposition states into classical ones. Because weak measurements could in principle allow errors to be detected in quantum states without destroying those states in the process, the work might be used to improve error correction in quantum computers.

LIGO reveals quantum correlations at work in mirrors weighing tens of kilograms

To Haocun Yu and Lee McCuller of the Massachusetts Institute of Technology and their colleagues on the LIGO Scientific Collaboration for showing that quantum-scale correlations can leave their mark on macroscopic objects weighing tens of kilograms. The team explored the exquisite interplay between the laser beam of a LIGO interferometer and its mirrors – each of which weighs 40 kg. They observed that radiation noise contributes to the motion of the mirrors, which is a result of Heisenberg’s uncertainty principle. When using squeezed vacuum states of laser light they showed that the quantum noise drops below the standard quantum limit, which demonstrates quantum correlations between the laser beam and the mirrors. The research could lead to the improved detection of gravitational waves by LIGO and similar observatories.

Thin-film perovskite detectors slash the imaging dose

To Wanyi Nie and colleagues at Los Alamos National Laboratory for using thin-film perovskites to create an extremely sensitive X-ray detector. Using a synchrotron beamline to characterize their thin-film perovskite detectors, the researchers found that the X-ray absorption coefficients of the perovskite materials were on average 10 to 40 times higher than that of silicon for higher-energy X-rays. They also demonstrated that the new X-ray detectors are 100 times more sensitive than conventional silicon-based devices. This new type of solid-state X-ray detector could enable medical and dental imaging at extremely low radiation dose, enabling the same quality image to be generated using a much-reduced X-ray dose, making scans safer for patients. Nie also notes that it should be possible to fabricate large-scale detector arrays at far lower cost than for semiconductor detectors.

Borexino spots solar neutrinos from elusive fusion cycle

To the Borexino collaboration for observing neutrinos from the carbon–nitrogen–oxygen (CNO) cycle in the Sun. To do so the team had to first painstakingly minimize the effects of background radiation in the Borexino detector, which comprises 278 tonnes of ultrapure liquid scintillator located deep inside Italy’s Gran Sasso mountain. The observation confirms a theory of stellar nucleosynthesis first proposed more than 80 years ago and will encourage physicists to use the next generation of neutrino detectors to try to resolve the “metallicity puzzle” of the Sun – a mystery regarding the abundance of carbon, nitrogen and oxygen in the star.

First observation of a ferroelectric nematic liquid crystal

To Noel Clark and colleagues at the University of Colorado Boulder and the University of Utah in the US, for observing a ferroelectric nematic phase of matter in liquid crystals more than 100 years after it was predicted to exist. In this phase, all the molecules within specific patches, or domains, of the liquid crystal point in roughly the same direction – a phenomenon known as polar ordering that was first hypothesized by Peter Debye and Max Born back in the 1910s. Clark and colleagues found that when they applied a weak electric field to an organic molecule known as RM734, a striking palette of colours developed towards the edges of the cell containing the liquid crystal. In this phase, RM734 proved far more responsive to electric fields than traditional nematic liquid crystals. Although further work is required to identify materials that display the phenomenon at room temperatures, ferroelectric nematics could find applications in areas from new types of display screens to reimagined computer memory.

Fundamental constants set upper limit for the speed of sound

To Kostya Trachenko of Queen Mary University of London, Bartomeu Monserrat and Chris Pickard of the University of Cambridge and Vadim Brazhkin of the Russian Academy of Sciences for calculations showing that the upper limit on the speed of sound in solids and liquids depends on just two dimensionless quantities – the fine structure constant and the proton-to-electron mass ratio. The team’s theoretical prediction is backed up by experimental data of the speed of sound in a range of solid materials and a calculation of the speed of sound in metallic hydrogen – a material that is yet to be created in the lab but should have the fastest speed of sound. The research provides insight into how fundamental constants impose bounds on physical properties.

Expanding twistronics to photons

To Andrea Alù, Qiaoliang Bao, Cheng-Wei Qiu and an international team of collaborators at the City University of New York, National University of Singapore, Monash University, China University of Geosciences and the University of Texas at Austin, for showing that dispersion- and diffraction-free propagation of light is possible, with a resolution that beats the diffraction limit by more than an order of magnitude, in twisted layers of 2D molybdenum trioxide. Their work builds on the discovery of “magic-angle” graphene – Physics World’s Breakthrough of the Year in 2018 – by using twisted layers of 2D materials to change the behaviour of propagating photons, rather than electrons. Just as the electron version of twistronics has led to a flurry of research on superconductivity and electron states, the new photonics variant has important implications for nano-imaging, quantum optics, computing and low-energy optical signal processing.

Mixed beams enhance particle therapy accuracy

To a team headed up by Joao Seco at the German Cancer Research Centre and Simon Jolly at University College London (UCL), for demonstrating how a mixed particle beam could enable simultaneous cancer therapy and treatment monitoring. The idea is to use a beam containing both carbon ions, which provide therapeutic irradiation of the target tumour, and helium ions, which travel straight through the patient and can therefore be used for imaging. In experiments at the Heidelberg Ion Beam Therapy Center using pelvis phantoms, the researchers showed that even small inflations of an air balloon inside the phantom caused an observable change in helium range. They also demonstrated that small phantom rotations changed the measured signal. The experiments reveal the potential of using a mixed beam to monitor intra-fractional anatomy changes, enabling more accurate delivery of particle therapy and, ultimately, providing better outcomes for cancer patients.

The first room-temperature superconductor

To Ranga Dias and colleagues at the University of Rochester and the University of Nevada Las Vegas in the US for observing superconductivity at temperatures up to 15 °C in a hydrogen-rich material under immense pressure. Superconductors carry electrical current with no electrical resistance and have a range of applications from the high-field magnets used in MRI scanners to particle accelerators. Practical devices based on superconductors must be chilled to very cold temperatures, which is costly and can involve the use of helium, so a long-standing goal of condensed-matter physicists has been to develop a material that is a superconductor at room temperature. The carbonaceous sulphur hydride material made by Dias and colleagues shattered the previous high-temperature record by about 35 °C and was the first to claim room-temperature superconductivity. While a pressure of 2.6 million atmospheres was required to achieve room-temperature superconductivity, the researchers think it may be possible to reduce the pressure by changing the chemistry of the material.

Physics societies call for sustainable approach to open access

A group of 16 major physics societies around the world have come together to support open-access publishing and welcome the increased “policy momentum” towards it. Yet in a joint statement, the societies urge policy makers to preserve the “diversity, quality and financial sustainability” of peer-reviewed publishing. They also warn that certain policies, such as the proposed cOAlition S “rights retention strategy”, could “undermine the viability of high-quality hybrid journals”.

Physics has been at the forefront of open access ever since the arXiv pre-print server was founded in 1991. While arXiv provides access to early drafts of scientific articles, the final peer-reviewed versions of the papers have traditionally been accessible to readers only through an institutional subscription. Open-access publishing, however, removes the requirement for subscriptions: by charging authors instead a fee, known as an article-processing charge (APC), articles are made immediately and freely available for anyone to read.

Over the past decade, the total number of papers in physics has grown by an average of 2% a year, but the number of open-access papers in physics has surged by about 25% a year. Despite this progress, however, more than 85% of physics articles are published in “hybrid journals”, which are publications that remain subscription based but give authors the choice to make their papers open access by paying an APC.

Undermining quality

One of the biggest open-access drives underway is Plan S, which seeks to make research papers open access immediately after publication. Unveiled in September 2018 by 11 national research funding organizations — dubbed cOAlition S – their goal is that from 2021 “all scholarly publications on the results from research funded by public or private grants provided by national, regional and international research councils and funding bodies, must be published in open access journals, on open access platforms, or made immediately available through open access repositories without embargo”.

Backed by funding bodies such as UK Research and Innovation and the French National Research Agency, Plan S does not support the hybrid model but acknowledges a “transitional pathway” towards fully open access “within a clearly defined timeframe, and only as part of transformative arrangements”. cOAlition S has also developed its rights retention strategy, which would give researchers supported by a cOAlition S Organizations “the freedom to publish in their journal of choice, including subscription journals, whilst remaining fully compliant with Plan S”.

Significantly, however, cOAlition S wants publishers to modify their existing publishing agreements so that authors can make their “accepted manuscripts” -- those that have been accepted for publication and include author-incorporated changes suggested during peer review but may not be in their final form -- available at the time of publication under a “CC BY” licence. Such a move would allow the work to be copy and distributed with attribution.

The 16 societies, which include the Institute of Physics, which publishes Physics World, as well as the American Physical Society and the Chinese Physical Society, maintain, however that the right retention policy would “undermine the viability of high-quality hybrid journals”. They also say that the move would mean that many physics researchers “no longer have an adequate range of options or freedom of choice in where they publish their work”.

The societies instead call for a “pragmatic, inclusive and sustainable approach to open access”, which includes broader international financial support for open access to be in place before hybrid journals can fully transition to open access.

Ask me anything: Carol Marsh

What skills do you use every day in your job?

At the start of my career and during my doctorate I used physics and maths. I produced designs with VHDL – a hardware description language that takes code and converts it into digital circuits. It’s different from a software language like C++, which runs a sequential set of instructions; instead, VHDL creates components such as flipflops that run in parallel.

The skill I use most now is communication. I’m always talking to customers, members of my team and organizations that promote engineering and diversity and inclusion. I do a lot of mentoring, mainly for people who want to become professionally registered and I regularly give presentations on technical topics, or about women in engineering. But my main job is chairing design reviews, which lets me see everything that’s going on across the whole site – all the different designs, how they work, what challenges the teams are experiencing, and every now and again I can still help people with their technical problems.   

What do you like best and least about your job?

My job is to support a team of engineers and it’s wonderful to see someone who started off at the company straight out of university leading major projects several years later. It’s great to see them grow; I really enjoy that. I also like doing a wide range of activities: often I don’t know what I’m going to be doing on any given day. It can change instantly from updating a process, ordering licences, approving designs for release to the customer, or helping members of my team. The thing I like least is the number of meetings I have to attend; some days my diary is just full of them.

What do you know today, that you wish you knew when you were starting out in your career?

I wasn’t confident when I was younger. When someone asked me to develop a design, I’d look at it and think “How am I going to do this?” But over the years, I’ve learned to take really complicated problems and break them down into smaller parts that I can solve. So if I could go back, I’d tell myself to be more confident and learn from my mistakes. In engineering, if you’re not learning you’re not growing. In school, you’re told that failure is a bad thing, but in engineering it is an opportunity to learn – you have to stay flexible and adapt to new information as soon as you receive it, while remaining confident about your skills. That ability to adapt is becoming more and more important in engineering. I also wish I had a crystal ball, as 30 years ago I had no idea how phenomenal the electronics we have would become. I give talks about what I think the impact of electronics will have over the next 30 years and it’s going to be absolutely incredible.

Optical sensor offers non-invasive monitoring of intracranial pressure

Traumatic brain injury is a major cause of death and disability. When a patient attends an A&E or neurocritical care unit with a head injury, one of the most important parameters to assess injury severity is intracranial pressure (ICP), as raised ICP is particularly associated with poor outcome. Measuring ICP, however, is currently a highly invasive process.

Speaking at the recent IOP symposium “Optics in Clinical Practice”, Panicos Kyriacou from the Research Centre for Biomedical Engineering at City, University of London described his team’s work in designing a non-invasive optical sensor technology for dynamically measuring ICP.

Measurement of ICP requires a surgeon to drill a hole in the patient’s skull and insert a pressure transducer (the ICP bolt). As well as being one of the most invasive non-therapeutic procedures, it cannot be performed at the site of an accident and carries large associated risks. “Stabbing a transducer into your brain carries certain risks – haemorrhage, leakage of cerebrospinal fluid or infection – and requires an expert neurosurgeon to perform the procedure. There needs to be a measured decision as to whether a patient really needs an ICP bolt,” Kyriacou explained.

As such, much research effort is now underway to develop methods for non-invasive ICP (nICP) monitoring. Currently, however, there is not a practical dynamic measurement that can rapidly determine absolute ICP values in mmHg.

“Our vision is to have a standalone ICP monitor that is completely non-invasive. Such a device will be placed on the forehead and will continuously monitor ICP in absolute numbers, as well as providing graphical ICP trends during monitoring,” said Kyriacou. “The vision of this research is to create a disruptive technology that will replace the most invasive monitor in clinical practice.”

Optical sensing

To create the nICP detector, Kyriacou and colleagues, along with clinical partners from the Royal London Hospital, developed an optical sensor based on photoplethysmography (PPG), which uses light to measure variations in blood volume. The device emits near-infrared light at various wavelengths into the skull and the reflected optical signals are detected by proximal and distal photodiodes. The proximal photodiode detects superficial PPG signals arising from layers of the forehead or scalp. These can be subtracted from the PPG signals read by the distal photodiode, which detects photons from deeper into the brain.

As a first step in evaluating the developed sensor technology and the capability of the acquired optical signals to reflect changes in ICP, the research team performed an in vitro evaluation using a custom made brain phantom. Kyriacou explained that this was a necessary step, as “obviously, we couldn’t recruit volunteers and put bolts in their heads to evaluate the sensor prior to clinical trials”.

The researchers created a brain phantom incorporating vessels with pulsatile flow and contained within a chamber (representing the scalp) that could be pressurized. They placed the optical sensor on the top surface of the phantom and raised the pressure inside the chamber from 10 to 40 mmHg (intracranial pressures of interest to neurosurgeons). Altering the pressure resulted in clear changes in the recorded PPGs.

Key to the success of the nICP device is knowing which features in the PPG trace are directly related to changes in ICP. The researchers examined various features and found two that had a large dependence upon the pressure. They then used these two features to create an ICP prediction model.

The team ran the in vitro experiment three times and saw excellent agreement between the nICP and invasive ICP readings, with correlations of 0.95–0.98 and RMS errors of 1.45–3.12 mmHg for the three datasets. These findings gave the team the confidence to perform in vivo tests on healthy volunteers. While there was no gold-standard comparison in this case, they observed promising trends in ICP measured on volunteers during tilting and Valsalva manoeuvres.

Clinical study

In the most recent phase of this work, the researchers joined forces with the Royal London Hospital, which has one of the largest neurological trauma centres in the UK, to begin clinical trials of the nICP device. They recruited patients that had an intracranial bolt (the gold standard for ICP) as part of their routine monitoring. This pilot clinical study, which began in February 2019 (paused earlier this year as the pandemic struck, and since resumed), has so far evaluated 21 of a targeted 40 patients.

Kyriacou shared some early results, noting that “the results were somewhat too good to be true”. A preliminary data analysis from a small group of patients revealed a high correlation between nICP and gold-standard measurements, with an RMS error of 1.98 mmHg. The nICP device showed a sensitivity of 95% and a specificity of 97% at 20 mmHg.

“These preliminary results generated a lot of excitement and enthusiasm. But this is a small group of patients, the robustness and confidence will come when we analyse all 40 patients, we are still recruiting and still analysing data,” Kyriacou concluded, noting that the group is hoping to commercialize the sensor. “Hopefully, we will be able to translate our research and create a tool to be used for patients and improve their quality-of-life.”

Face shields cannot protect wearers from virus particles carried by vortex rings

Vortex rings created when a person sneezes can transport virus particles to the noses of people wearing face shields – according to fluid dynamics simulations done by Fujio Akagi and colleagues at Fukuoka University in Japan. Their research reveals how these complex flows allow air-carried particles to enter the gaps between a shield and its wearer’s face. Their discovery exposes a key weakness in existing protective equipment and could lead to face shield designs that are better at diverting airflows away from wearers.

When fluids (liquids and gases) are fired at high velocity through a circular aperture such as the mouth or a nostril, swirling vortex rings can be created. As well as concentrating and focussing particles emitted in a sneeze or cough, these rings can also gather and transport particles that happen to be in the surrounding air.

Due to the COVID-19 pandemic, people are using protective equipment that aims to prevent this type of virus spread. For many healthcare and service workers, transparent face shields are a popular choice, owing to their increased comfort compared with face masks. Previously, fluid dynamics simulations have been used to study how these shields can reduce airflows generated by their wearers during sneezing. So far, however, there has been little work done on how effective face shields are at protecting wearers from the coughs and sneezes of others.

One metre sneeze

Akagi’s team did computer simulations of the airflow surrounding a person wearing a popular design of face shield. The person is exposed to the sneeze of a person standing 1 m in front of them. The team discovered that high-velocity vortex rings can reach the top and bottom edges of the shield within just 1 s. At this point in time, the wearer’s breathing can draw particle-carrying air into the narrow space between the shield and their face.

If the timing of the sneeze’s arrival is synchronized with inhalation, the simulations reveal that over 4% of the particles carried by the vortex ring can reach the vicinity of the wearer’s nose – significantly enhancing their risk of infection. Therefore, without additional protection like a face mask, they concluded that face shields are not highly effective for preventing the spread of COVID-19.

With this weakness exposed, Akagi’s team hope that their results will help guide the development of standards for protective measures against the spread of the virus. In the future, they hope to study how vortex ring flows are altered in different ways by face shields with different shapes. This work could soon lead to optimized shield designs that prevent users from inhaling particles, without the need for any additional protection.

The research is described in Physics in Fluids.

Learning the lessons from the Haiyuan quake 100 years on

On 16 December 1920 at about 7 p.m. local time, a magnitude-7.9 earthquake ripped along 240 km of fault in north-central China, razing two cities to the ground and severely damaging five others. It was one of the most devastating earthquakes ever seen and around 230,000 people died. Today, on the centenary of the Haiyuan quake – known colloquially as “the mountains walked” – researchers at the American Geophysical Union (AGU) Fall meeting are discussing how to better prepare for the next “big one”.

One of the reasons that the quake was so deadly is because it took people by surprise: the last major earthquake on this fault occurred over 1000 years earlier. Long periods of inactivity are a common feature of earthquakes on continental plates and in the intervening years cities are unwittingly built right over the hidden fault. Large swathes of the world, including regions from the European Alps to the Himalayas and much of the US, are prone to continental quakes. Luckily, continental faults tend to be easier to study than oceanic ones. “Unlike off-shore faults, which are very difficult to access, it is possible to set up geophysical sensors along continental faults and dig trenches on the surface to understand their long-term behaviours,” says Zhigang Peng from Georgia Institute of Technology in Atlanta, who has organized the AGU Haiyuan quake session.

In recent decades sophisticated Earth surveillance techniques including satellite and drone imagery, LiDAR scans and GPS measurements have enabled researchers to pick up on early signs of continental fidgeting. For example, Wenqian Yao, from the China Earthquake Administration, and colleagues have used unmanned aerial vehicles to survey the landscape along the Haiyuan fault system. Combined with measurements of slip rate on the ground they have discovered that strain is building on an offshoot of the Haiyuan fault, known as the Zihong Shan fault. Their findings suggest that the Zihong Shan fault could produce a quake of up to magnitude-7.

Today scientists are making long-term seismic hazard maps in many countries

Zhigang Peng

Similarly, Yacine Nicolas Benjelloun and colleagues from Institut de Physique du Globe de Paris have used drone images to map two major continental faults in Northwestern Mongolia, known to have produced a magnitude eight quake in 1905. Combining the drone data with geological history of fault movement has enabled them to estimate the seismic hazard for this region – an approach that they believe could be applied anywhere.

James Neely and Seth Stein from Northwestern University, meanwhile, have used the last 40 years’ worth of quake data to categorize continental earthquakes all over the world. Using this information they have been able to divide continental quakes into four categories and show that normal faults – where the crust is being stretched apart – have a maximum magnitude of seven, while other continental fault geometries can reach magnitude eight. For engineers, this kind of information is vital as designing buildings and infrastructure to withstand a magnitude eight is significantly more complex and expensive than for a magnitude seven (which is 10 times smaller than a magnitude eight).

Fault lines

Despite all the technology available to us today, researchers remain humble towards continental quakes. Some faults accumulate strain so slowly that they are invisible to modern instruments right up until the moment they move. The 1994 Northridge quake in California was an example of this, with no-one having any idea that this suburb of Los Angeles sat atop a major earthquake fault. And even when researchers identified a fault they don't know how much strain will make it pop, or how the fault will move. “We don't know if an earthquake is going to grow large and rupture several faults, or stay small and confined to a single fault,” says Neely.

As a result, the main focus of research today is to estimate the seismic hazard of a region and make preparations. For example, a report submitted to the German Federal Parliament in November outlines the chance of a major earthquake near the city of Cologne and makes recommendations for mitigating such an event. The findings shows that this region should expect a quake with a magnitude of 6.5 every 1000 to 3000 years. If such a quake occurred tomorrow the researchers estimate that around 10,000 buildings would suffer moderate to severe damage and somewhere between 100 and 1000 people would die.

As the 2008 Sichuan quake in China and the 2010 quake in Haiti demonstrate, we still have a long way to go when it comes to protecting ourselves from continental quakes. But Peng and his colleagues think that significant progress has been made. “In the 1920s, the concept of an active fault within continents was very new,” he says. “Today scientists are making long-term seismic hazard maps in many countries.” Peng adds that buildings are also generally much stronger than one century ago and people are “generally more aware and know how to stay safe during these events”.

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