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Non-thermal atmospheric plasma enhances bone fracture healing

Bone fracture or loss, caused by trauma, surgery or disease, is a serious medical problem. After bone damage, the healing process depends largely on the severity of the fracture. Several approaches have been developed to accelerate bone repair, including both physical and biological methods. However, existing techniques come with limitations, such as the inability to fully restore the bone’s functionality with minimal scar formation. Bones can be re-combined, but achieving bone regeneration remains a complex task.

Scientists at Osaka City University (OCU) have therefore explored the properties of non-thermal atmospheric pressure plasma (NTAPP) to induce direct bone regeneration within damaged bones. Plasma, the fourth state of matter in which gas becomes ionized, is composed of electrons, ions, high-energy photons and neutral particles. Most artificial plasmas are generated using electrical energy.

Following on from its use in industrial applications, plasma is now also used in medicine and bioengineering, accelerated by the development of NTAPP sources. While typical plasmas have estimated temperatures of around 10,000 K, NTAPP can be generated at room temperature and atmospheric pressure. This can create unusual situations in which strongly reactive species exist near biological targets such as cells, tissue and bone. It is thought that low levels of these plasma-generated reactive species can stimulate cell proliferation, although above a threshold dose, they can cause cell death.

Principle investigator Jun-Seok Oh previously developed a helium microplasma jet that minimizes thermal damage to the biological target and maximizes generation of reactive species. Co-principal investigator Hiromitsu Toyoda suggested investigating the use of this plasma for bone regeneration in an animal model.

In their latest study, published in PLOS One, researchers at OCU’s Graduate School of Medicine and Graduate School of Engineering describe the configuration and assembly of this microplasma jet system. The device generates reactive oxygen and nitrogen species, including positive and negative ionic species in the glowing plasma jet, and excited neutrals in an invisible downstream gas flow, into which the biological tissue is placed.

Single plasma treatment heals critical bone defect

Plasma has been used previously as a direct treatment for wound healing or to indirectly generate reactive oxygen species by provoking stem cell proliferation. However, orthopaedic surgeons have faced challenges deploying plasma as a single approach for treating bone fractures. As such, Toyoda and Oh consider NTAPP to be a new therapeutic method.

In this investigation, the team examined 10 female rabbits with an average weight of 3.5 kg. Following sedation and creation of a 10 mm critical bone defect in the animals’ ulnar shaft, the rabbits received a single session of plasma irradiation for 5, 10 or 15 minutes. X-ray images acquired at two-week intervals for eight weeks showed that the plasma-treated bone defects were healed.

Repairing injured bones: X-ray images showing bone defect healing two to eight weeks after various plasma irradiation times. Eight weeks after treatment, the images show bone continuity, suggesting bone regeneration and fracture healing. (Courtesy: CC BY 4.0/*PLoS One* 10.1371/journal.pone.0255861)

Eight weeks after the plasma treatment, the researchers surgically removed and further analysed the animals’ ulnar bones to assess the potential of NTAPP for bone regeneration. Micro-CT images revealed that a single session of plasma treatment stimulated bone fusion in the injured bones without the need for an artificial bone support system. In another histological evaluation, the researchers discovered that ingrowth of new bone in the plasma-irradiated animals was improved compared with a non-irradiated control group. This further confirms that plasma treatment can create a near-perfect continuity with the neighbouring bones following injury.

Cold atmospheric plasma eradicates residual cancer cells

The helium microplasma jet system deployed in this study delivers plasma discharge close to the injury. The authors suggest that plasma interaction near to the tissue surface could stimulate the generation of reactive oxygen species and may contribute to an increased biological effect during the bone regeneration process. However, the plasma dose and rate of discharge required to optimize fracture healing are unexplored, and it is currently unclear whether the dose-to-surface distance during treatment will affect the healing capacity of plasma irradiation in injured bones.

The researchers are now exploring the cellular and biological processes that occur after plasma irradiation, to lay the foundation for effective clinical translation in the future.

The ten-billion-dollar gamble: Keeping the JWST cool

Of the four instruments aboard the James Webb Space Telescope (JWST), three – the Near Infrared Spectrograph (NIRSpec), the Near-Infrared Camera (NIRCam) and the Fine Guidance Sensor/Near Infrared Imager and Slitless Spectrograph (FGS/NIRISS) – operate at near-infrared wavelengths of 0.6 to 5 μm. For them, the telescope’s general, solar-shielded operating temperature of 36 K is cold enough. The fourth instrument, however, is designed to observe at longer wavelengths of 5 to 28 μm. For that, it needs even lower temperatures – 29 K colder than the other instruments, to be precise.

To keep the arsenic-doped silicon detectors on the Mid-Infrared Instrument (MIRI) at their operating temperature of 7 K, NASA has built the most sophisticated cryocooler ever launched into space. To call it a big refrigerator would be simultaneously accurate and a gross disservice to the innovations required to make it work.

The cryocooler’s main section is its Cryocooler Compressor Assembly (CCA). Housed in the spacecraft bus, on the warm side of the telescope, it uses helium as a refrigerant, and is connected to MIRI (located about 10 metres away in the Integrated Science Instrument Module, behind the telescope’s primary mirror) by a labyrinth of tubes. Once the helium has been conductively chilled by a precooler inside the CCA, it gets pumped through these tubes to MIRI via the Cryocooler ColdHead Assembly (CHA). This device contains a valve less than a millimetre wide that acts as a “throttle” for the helium. As the helium expands on the other side of the valve, it drops to 6 K (one degree below MIRI’s operating temperature) thanks to the Joule-Thomson effect. It then passes behind MIRI’s detectors, picking up and exchanging their excess heat.

Space challenges

In a terrestrial cryocooler, such a system would be straightforward. In a cooler located on board a telescope in deep space, however, it creates certain challenges. An example is the distance between the pre-cooler and the helium-throttling valve. Normally, these two components are just centimetres apart, but on the JWST they are separated by many metres. Keeping the helium refrigerant cool on its journey though the telescope’s plumbing is therefore vital.

Another challenge is vibration. Any cryogenic system that contains moving parts will produce some vibrations, but aboard the JWST these vibrations need to be virtually non-existent, since any jitter from moving machinery could shake the optics and produce blurred images. Consequently, Webb’s cryocooler contains only two moving parts: a pair of horizontally opposed piston pumps in the CCA that are specially designed to operate with exceptional smoothness.

One of the many unknowns surrounding the JWST is how long it can operate without astronauts to service it. Many factors – from a failure to deploy successfully to malfunctioning instruments that can’t be repaired because the telescope is out of the reach of astronauts – could end its mission prematurely. However, unlike two of its predecessors, NASA’s Spitzer Space Telescope and ESA’s Herschel Space Observatory, it will not run out of coolant, because its cryocooler is a closed system. From a cooling perspective, then, the JWST should be fit to see out the decade, operating alongside other ground- and space-based instruments scheduled to come online in the mid- and late-2020s.

Next: The JWST’s micro-scale windows on the universe

This article was amended on 22 December 2021 to reflect delays to the JWST’s launch date.

Medical physics and biotechnology: highlights of 2021

This year, researchers have once again had to deal with conferences going virtual and bouts of working from home. But that hasn’t stopped the medical physics community from continuing to develop and investigate advanced healthcare techniques and tools. Alongside ongoing efforts to help detect, analyse and prevent the spread of the SARS-CoV-2 virus, 2021 has seen also the introduction of novel cancer treatments, advances in diagnostic imaging technology and innovative new biomedical devices. Here are just a few of the research highlights that caught my eye this year.

Antibody therapy delivered directly into the brain

For the first time ever, researchers have delivered antibody therapy directly into the brain, to target breast cancer metastases. A team at Sunnybrook Health Sciences Centre used MR-guided focused ultrasound to non-invasively and temporarily open the protective blood–brain barrier (BBB), enabling the monoclonal antibody trastuzumab to reach specific areas of the brain. The researchers report the results from the first four patients in an ongoing clinical trial, all of whom had breast cancer with brain metastases.

The team used Insightec’s ExAblate device to perform transcranial focused ultrasound while simultaneously delivering intravenous trastuzumab. The drug was radiolabelled with ¹¹¹In, enabling it to be visualized using SPECT. After BBB opening, the SPECT images showed that trastuzumab precisely targeted the brain tumours. MR imaging revealed that patients’ tumours shrank by between 7% and 31%, at up to four months after treatment. Importantly, the procedure caused no serious adverse effects.

Clinical linac produces FLASH beam

A team from Dartmouth has developed a method to convert a standard clinical linear accelerator (linac) used for radiation therapy to deliver a FLASH-capable, ultrahigh-dose rate radiotherapy beam. The process, which uses existing accessories, takes only 20 minutes to perform, or to reverse.

The researchers converted a Varian Clinac 2100 C/D to deliver ultrahigh-dose rate electron beams. The converted system could achieve dose rates of up to 290±5 Gy/s at the isocentre (at a source-to-surface distance of 100 cm), well above the reported 40 Gy/s threshold needed to potentially achieve the FLASH effect. They note that after conversion, the beam can be used in a conventional geometry with the patient on the treatment couch. The group is using the ultrahigh-dose rate beam in preclinical studies, as well as in clinical veterinary treatments of dogs with sarcoma tumours.

A disappearing pacemaker

Temporary cardiac pacemakers provide pacing for patients with short-term heart rhythm disorders. But such devices typically use leads inserted through the skin and require surgical removal when no longer needed. A team headed up at Northwestern University and The George Washington University has developed an implantable cardiac pacemaker with no external leads that provides post-operative control of heart rate and rhythm, and then completely dissolves in the body after completion of therapy.

The pacemaker is made entirely from bioresorbable materials, and receives power and control commands via wireless energy transfer. The researchers demonstrated successful pacing in ex vivo animal hearts and human cardiac tissue, and in vivo in a dog during open-chest surgery. They also implanted the pacemakers in rats and performed daily pacing trials on the animals, observing successful ventricular capture.

First positronium image recorded during a PET scan

Positron emission tomography (PET) is a molecular imaging tool commonly employed for cancer diagnosis. During a PET scan, positronium is also generated in the patient’s body, but current PET systems are not able to acquire positronium images. A research group headed up at Jagiellonian University has now created the first-ever positronium image recorded during a PET scan. Their goal is to use positronium imaging to distinguish between healthy, cancerous and inflammatory tissues.

The Jagiellonian-PET detector — Full-scale prototype: The Jagiellonian-PET system. (Courtesy: Kamil Dulski, Jagiellonian University)

The researchers developed a method for positronium lifetime imaging using the Jagiellonian-PET (J-PET) scanner, which is based on low-cost plastic scintillators arranged in concentric layers and read out by photomultipliers. Images of cancerous and healthy tissue samples exhibited significant differences in positronium lifetime, suggesting that this approach could help determine the degree of cancer malignancy in vivo without the need for surgical biopsy. Next, the team aims to construct a high-sensitivity total-body J-PET and perform positronium imaging in vivo.

The world’s first photon-counting CT scanner

Computed tomography, or CT, is a ubiquitous X-ray imaging technique used to perform more than 300 million medical imaging exams globally each year. Now, following than 15 years of research, Siemens Healthineers has unveiled the world’s first photon-counting CT scanner, the Naeotom Alpha.

Conventional CT requires two conversion steps to create a medical image: X-ray photons collected by a scintillator are used to generate an optical signal, which is then converted into an electrical signal. Photon counting CT, however, enables one-step conversion straight from X-ray photons into an electrical current. This provides dramatic imaging improvements, including increased resolution and a reduction in radiation dose by up to 45% over conventional CT detectors. Photon counting technology also makes it possible to assess the energy level of each and any photon separately.

Physics World‘s Breakthrough of the Year coverage is supported by Bluefors, a leading supplier of cryogen-free dilution refrigerator measurement systems with a strong focus on the quantum computing and information community. Our aim is to deliver the most reliable and easy to operate systems on the market which are of the highest possible quality.

Physics teachers inspire the next generation of scientists

According to the latest annual survey of UK graduates by Prospects Luminate, secondary education is the third most popular professional career choice for physics graduates. Indeed, for anyone who enjoys discussing fundamental scientific concepts with young and curious minds, teaching physics at secondary school promises a fun, rewarding and varied work environment.

“I wanted a job that would make me happy,” says Oliver Alexander, who gave up the opportunity to pursue a lucrative career as a patent attorney to become a physics teacher. “I wanted to help and influence people, and teaching physics to secondary school students has the potential to change their whole lives.”

I was miserable in a desk job and I knew I needed to do something else. Being a teacher is crazy in a good way. I haven’t had a dull moment since I started.
Oliver Alexander

Alexander admits to having some reservations about switching tack and taking an extra year to retrain – above all whether he would be good enough to communicate the beauty and complexity of physics to a classroom of teenagers. But now, in his first full year as a trained physics teacher, he has no regrets.

“I was miserable in a desk job and I knew I needed to do something else,” he says. “Being a teacher is crazy in a good way. I haven’t had a dull moment since I started.”

Part of that enjoyment is getting to know his students and classes, and seeing just how quickly they develop their scientific knowledge and skills. Aidan Reynolds, who has also just completed his first term as a physics teacher, can already sense the progress his students are making.

“During my training year I mainly taught A-level students, but now I have some classes who are just starting to tackle some GCSE topics,” he says. “They are newer to the subject, and you can really see them develop their understanding from one day to the next.”

Physics to the fore

Breaking it down: New physics teacher Aidan Reynolds enjoys finding new ways to explain complex scientific ideas to secondary-school students (Courtesy: A Reynolds)

Reynolds and Alexander relish the opportunity to discuss and explore physics ideas with their students, and they work hard to devise different teaching approaches to help different age groups to properly understand fundamental physics phenomena. “It can be tricky to get some of the complex ideas across, particularly when you have studied them in such depth at university,” comments Reynolds. “It’s quite a fun challenge to take something that I know is very complicated, and making it simpler by breaking it down into its key component parts.”

With physics teachers still in short supply, Reynolds often has the opportunity to cover more advanced topics with A-level groups to help them prepare for university admissions. “Tackling those harder questions keeps my physics brain ticking over,” he says.

It’s a fun challenge to take something that I know is very complicated, and making it simpler by breaking it down into its key component parts.
Aidan Reynolds

For anyone thinking about becoming a physics teacher, both Alexander and Reynolds have a simple piece of advice: “Go for it!” Reynolds adds that it can be a good idea to try to spend a day or a week in a school to get a feeling for the environment. “I also did some tutoring, which makes you start thinking about how you would explain key concepts to different age groups,” he says. “When you go and observe some lessons you realize that it’s not as scary as it might seem from the outside.”

Both Alexander and Reynolds were supported through their postgraduate training year by the Institute of Physics (IOP), which runs a scholarship programme funded by the Department for Education for trainee secondary-school physics teachers in England. The Teacher Training Scholarship scheme offers successful candidates tax-free funding of £26,000 to support them through their training year, as well as a structured programme of continuing professional development to help scholars develop more effective approaches for teaching physics. Trainee teachers accepted onto the scheme also benefit from IOP membership during their training year, as well as access to a vibrant community of fellow scholars.

Has this article inspired you to consider a career in teaching? Take our short survey and tell us your views.

“My postgraduate training gave me lots of general teaching skills, but the IOP scholarship provided a more direct connection to the physics,” says Reynolds. “The conferences and lectures organized by the IOP as part the scholarship helped me to apply the general techniques I learnt during my teacher training to physics. Talking to other teachers who are passionate about physics education also really helped me to develop my explanations, particularly for the younger age groups.”

Making a connection

Both Reynolds and Alexander enjoy the social interactions with their classes and, after just a few weeks of teaching in their new schools, they are starting to make personal connections with their students. “They start talking to you about why they are interested in different subjects and what they want to do later on,” says Alexander. “Today a student came to tell me that he’d applied to college, and I was really happy that he had wanted to share that success with me.”

One term into his first academic year, and Alexander can already see the impact his teaching has had on his students. “At the start of year they didn’t know how to go about solving a problem,” he comments. “Now, when I ask a question on a new topic, they know how to approach it even if they don’t get it right first time. They’re thinking more like physicists, and that’s so lovely to see.”

Outside of the scholarship scheme, Reynolds still keeps in touch with a wider network of physics teachers through an e-mail group run by the IOP, the Physics Teaching News and Comment discussion forum (PTNC).

“There are so many teachers on the group who are sharing ideas and collaborating together to solve the same problems,” he says. “It’s absolutely amazing to be a part of that community and get that support, and I’ve found lots of resources on there that I’ve used myself or recommended to my students.”

The IOP also provides plenty of learning materials for physics teachers, including more than 2500 teaching activities that are freely available through its IOPSpark service, and it runs the Talk Physics forum for anyone involved in teaching physics in secondary school.

“Making the leap into teaching has definitely been worth it”, says Alexander, who has found his early days both challenging and rewarding. “There are definitely stressful days, and times when you feel like you’ve messed everything up, but for every day like that there are two or three where everything goes right,” he says. “When it all clicks into place you feel like you have had a huge impact.”

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Applications for the IOP Teacher Training Scholarship programme are open now. Find out if you are eligible and apply today.

The ten-billion-dollar gamble: How the JWST shields itself from the Sun

Because the James Webb Space Telescope (JWST) operates in infrared light, stray thermal emissions from the Sun, Earth and even the spacecraft itself could cloud its vision. To keep them out, mission scientists designed an intricate, tennis-court sized sunshield that is quite unlike anything NASA has attempted to deploy in space before.

The sunshield comprises five layers, or membranes, of an aluminium-coated polymer called Kapton that is widely used in space exploration thanks to its stability across a broad range of temperatures. This stability is crucial: the first, Sun-facing layer of the sunshield is expected reach 383 K while temperatures at the inner fifth layer will drop as low as 36 K. Even with the right material, though, designing the sunshield’s layers to perform in deep space has been “a significant concern” says James Cooper, the JWST’s sunshield manager at NASA’s Goddard Space Flight Center.

Part of the problem is that each membrane in the sunshield will expand or contract to a different degree depending on its operating temperature. Accordingly, the membranes sitting in a clean room at Northrop Grumman (the aerospace firm that designed and built the sunshield) are not the same size as they will be in space. “Each membrane is carefully sized for its predicted temperature range,” Cooper explains. “Layer one – the Sun-facing layer – will be the hottest, while layer five will get very cold. So layer five has to be built ‘too big’ on Earth because we know that the material will shrink when it gets cold.”

Under tension

Another challenge is that each layer of the sunshield is gossamer-fine. The first, hottest layer is 0.05 mm thick, while the other four are 0.025 mm; their aluminium coatings are just 100 nm deep. Keeping the membranes thin saves weight, but it could also leave the sunshield susceptible to damage. What happens if it rips?

Cooper’s reply is that the sunshield is designed to cope with some level of damage. He and his colleagues expect it to suffer various wounds from micrometeorite impacts during its working life, and the odd hole here or there will not affect its performance – especially since they built a grid of seams and rip-stops into each layer to prevent tears from growing larger than approximately one by two metres. “We can meet performance requirements with this size tear in any layer,” Cooper tells Physics World.

The greatest risk of damage, though, comes soon after launch. Each of the kite-shaped sunshield’s six corners contains a membrane tensioning system (MTS), and each MTS is attached to 15 cables – three for each of the five membranes, amounting to 90 cables in all. To pull the sunshield’s five layers apart, the MTSs have to reel these cables in. A rip or catch at this unfurling stage could be very damaging indeed, and getting the system to work in rehearsals proved tricky.

“The MTS was relatively straightforward when bench-tested alone, but when we put everything together we found complex interactions with the membrane and cable management systems,” Cooper says. “We had to overcome challenges dealing with alternating tensions and slack in the cables.”

With the sunshield scheduled to begin unfurling three days after the telescope’s launch on 25 December, and taking five days to complete, it’s going to be a nervy New Year for Cooper and his colleagues as they wait to see whether the $9.8 billion telescope deploys successfully. But they won’t be the only ones biting their fingernails about keeping the JWST cool. While the sunshield will keep the telescope’s optics and most of its instruments at a frigid 36 K, some components need to be even colder.

Next: Keeping the JWST cool

This article was amended on 22 December 2021 to reflect delays to the JWST’s launch date.

Quantum effects make magnetene surprisingly slippery

The ultra-slippery nature of a two-dimensional material called magnetene could be down to quantum effects rather than the mechanics of physical layers sliding across each other, say researchers at the University of Toronto in Canada and Rice University in the US. The result sheds light on the physics of friction at the microscopic scale and could aid the development of reduced-friction lubricants for tiny, implantable devices.

Two-dimensional materials are usually obtained by shaving atomically thin slices from a sample of the bulk material. In graphene, a 2D form of carbon that was the first material to be isolated using this method, the friction between adjacent layers is very low because they are bound together by weak van der Waals forces, and therefore slide past each other like playing cards fanning out in a deck. For magnetene, the bulk material is magnetite, a form of iron oxide with the chemical formula Fe₃O₄ that exists as a 3D lattice in the natural ore. The bonds between layers are much stronger in magnetene than in graphene, however, so its similarly low-friction nature was a bit of a mystery.

Not just sliding layers

In the new work, which is published in Science Advances, lead author Peter Serles, together with colleagues led by Tobin Filleter, Chandra Veer Singh and Shwetank Yadav, obtained a sample of 2D magnetene by treating magnetite with high-frequency sound waves. This approach separated few-layer samples of magnetene from the bulk material. The team then measured the friction between the sheets using an atomic force microscope probe.

To their surprise, the researchers found that the friction between the tip of the AFM probe and the uppermost layer of magnetene was just as low as it is in the graphene. They therefore suspected that something other than layer sliding was at play. “When you go from a 3D material to a 2D material, a lot of unusual things start to happen due to the effects of quantum physics,” explains Serles. “Depending on what angle you cut the slice, it can be very smooth or very rough. The atoms are no longer as restricted in that third dimension, so they can vibrate in different ways. And the electron structure changes too. We found that all of these together affect the friction.”

To confirm the importance of these quantum phenomena, which include modifications to the charge density of the iron atoms and the emergence of unique low-damping phonon modes (vibrations of the crystal lattice) that are “forbidden” for classical systems, the team compared their experimental results to density functional theory simulations of how the probe slides over the 2D material. They found that the models that included quantum effects best predicted their experimental findings.

New ultra-low-friction materials

The work could help scientists and engineers design new ultra-low-friction materials in the future. Such materials could be useful as lubricants in small-scale applications like implantable devices, the researchers say. “When you’re dealing with such tiny moving parts, the ratio of surface area to mass is really high,” Filleter explains. “That means things are much more likely to get stuck. What we’ve shown in this work is that it’s precisely because of their tiny scale that these 2D materials have such low friction. These quantum effects wouldn’t apply to larger, 3D materials.”

The researchers say they would now like to better understand the role of the quantum effects, since the same low-friction behaviour has not been observed in other recently-synthesized 2D magnetic iron oxides such as hematene (Fe₂O₃) or chromiteen (FeCr₂O₄).

The ten-billion-dollar gamble: The JWST’s magnificent mirrors

Building a mirror the size of the James Webb Space Telescope’s (JWST) 6.5-metre primary isn’t a problem per se. Building a 6.5-metre mirror that can fit inside an Ariane 5 rocket fairing just 4.57 metres wide, without being too heavy to launch into space – well, that is a problem, and the task of solving it fell to NASA’s Lee Feinberg, who leads the telescope’s optical team.

“The primary mirror has a very elegant design,” Feinberg tells Physics World. The essence of that design, he explains, is that the primary mirror is foldable: the final version comprises 18 hexagonal segments, with three of the segments on either side forming “wings” that fold down.

The JWST also has a secondary mirror 0.74 metres across, plus a smaller tertiary mirror to remove the scope’s astigmatism and flatten the focal plane ready for its scientific instruments. Together, these three mirrors make up an arrangement known as an off-axis three-mirror anastigmat that corrects for spherical, coma and astigmatism errors while providing the instrument with a larger field of view. But these capabilities contribute launch headaches of their own. “The real trick is that the booms holding the secondary mirror are eight metres long, so you also have to fit that inside the rocket,” Feinberg notes. “And then there’s the sunshield. So we had to fold up for all those reasons.”

All three mirrors are made from a new type of gold-plated, optical-grade beryllium that remains stable at the telescope’s operating temperature of 36 K. This material, known as O-30, was created specially for the JWST by the materials firm Materion, and its advantages include a low mass and good technical performance at cryogenic temperatures. The material’s stiffness, for example, means that when the mirror is plunged into the freezing cold behind the telescope’s sunshield, it does not distort too much. Given all these factors, and the size of beryllium billets that were considered reasonable to work with, making a hexagonal segmented system that could fold up was “the best option”, Feinberg says.

A person in a clean-room suit looks on as one of the segments of the JWST mirror is tested — Looking good: A test unit of one of the hexagonal segments that make up the JWST’s primary mirror. (Courtesy: Drew Noel)

A similar hexagonal system has operated on the twin 10-metre Keck telescopes in Hawaii since the 1990s, and Feinberg acknowledges that his team learned a lot from Keck’s optical design. As at Keck, all 18 segments of the JWST’s primary mirror, as well as its secondary, have robotic actuators to nudge them into focus.

However, while Keck has sophisticated wavefront sensors to align its segments, the JWST optical team decided that such a system would be too complex to operate autonomously in deep space. Instead, the telescope will use its science camera. “The first test image that we’ll get will actually be 18 separate stars, because of the 18 separate segments each acting like a telescope,” Feinberg explains. The telescope will then use its camera and a specially developed algorithm called Phase Retrieval to measure the shape of the wavefront and adjust the shape of the primary mirror until all 18 segments focus as one.

The design of the telescope’s mirrors is typical of the technology and techniques that had to be pioneered to make the JWST workable. “Across the board, we felt that for everything we did, there was no playbook,” Feinberg says. “We were really changing the way we were doing things.”

A case in point: while the 2.4-metre mirror on the Hubble Space Telescope is contained within what is effectively a giant telescope tube assembly, the JWST’s mirrors are open to space. As the next post explains, protecting these mirrors from the heat and glare of the Sun is a tough challenge.

Next: How the JWST shields itself from the Sun

This article was amended on 22 December 2021 to reflect delays to the JWST’s launch date.

Brilliant polymath, troubled person: how John von Neumann shaped our world

Few mathematicians during the last century – perhaps only Bertrand Russell and Alan Turing – were as successfully polymathic as John von Neumann, the subject of the biography The Man from the Future: the Visionary Life of John von Neumann by Ananyo Bhattacharya, a science writer and former medical researcher with training in physics and protein crystallography. His book is well researched with the encouragement of von Neumann’s daughter, Marina von Neumann Whitman. It is also engagingly written, and mostly accessible to non-mathematicians, though it is inevitably intellectually demanding, ranging from the intricacies of quantum mechanics to the origins of electronic computing. As the author himself admits, with reference to a famous comment by Isaac Newton, “This book perches precariously on the shoulders of many giants.”

Born Neumann János in Budapest, Hungary, in 1903, von Neumann helped to lay the mathematical foundations of quantum mechanics in the late 1920s, while working in Germany (where he acquired the German form of his name). After moving to Princeton, US, in 1930, he was among the key scientists who worked on the Manhattan Project to build the atomic bomb. Around the same time, von Neumann published a treatise, Theory of Games and Economic Behavior, with the economist Oskar Morgenstern. Coining the phrase “zero-sum game”, the treatise would change economics and introduce game theory into political science, military strategy, psychology and evolutionary biology.

Post-war, von Neumann helped to design the world’s first programmable electronic digital computer, intended to make calculations about the hydrogen bomb. Then, in 1948, his automata theory launched the idea of information-processing machines capable of reproducing, growing and evolving. In the 1950s, his consideration of the workings of brains and computers made him a visionary thinker in artificial intelligence. Unfortunately, he could take this no further, because he died prematurely in 1957, aged 53, from cancer. Even so, writes Bhattacharya, “His thinking is so pertinent to the challenges we face today that it is tempting to wonder if he was a time traveller, quietly seeding ideas that he knew would be needed to shape the Earth’s future.”

His private life was less productive and rewarding, however. After von Neumann’s death, his second wife, computer scientist Klára Dán, who remarried for the fourth time before taking her own life in 1963, penned an unfinished memoir. Quoted in Marina von Neumann Whitman’s 2012 book, The Martian’s Daughter, the memoir’s chapter entitled “Johnny” opens as follows: “I would like to tell about the man, the strange contradictory and controversial person; childish and good-humoured, sophisticated and savage, brilliantly clever yet with a very limited, almost primitive lack of ability to handle his emotions – an enigma of nature that will have to remain unresolved.”

Von Neumann was one of a group of brilliant Hungarian mathematicians and physicists, including Leo Szilard, Edward Teller and Eugene Wigner, born around the turn of the century, who emigrated to the US and in many cases worked on the Manhattan Project. Most were from Jewish families, and humorously dubbed themselves “Martians” because they were outsiders to American society, apparently superhuman in intellect, speaking an incomprehensible native language and coming from a small obscure country.

Tellingly, von Neumann attributed their academic success to “a coincidence of some cultural factors” that created “a feeling of extreme insecurity in the individuals, and the necessity to produce the unusual or face extinction”. In other words, comments Bhattacharya, “their recognition that the tolerant climate of Hungary might change overnight” – as happened murderously in the White Terror of 1919–1921 – “propelled some to preternatural efforts to succeed”. Mathematics and physics were considered safe choices for Jews who wished to excel academically, because these subjects were viewed at that time as being relatively harmless and reasonably well rewarded. This is why the 1919 experimental proof of Einstein’s theory of general relativity was internationally honoured despite his Jewishness.

Both Einstein and von Neumann, who was 24 years his junior, settled at Princeton’s Institute for Advanced Study after it was established in 1930, and remained there until their deaths. But they responded to the place, and to America, in hugely polarized ways – as illustrated by von Neumann’s habit of playing German marching tunes at top volume on his office phonograph, provoking complaints from neighbouring offices, including Einstein’s. According to his friend Wigner, von Neumann “felt at home in America from the first day. He was a cheerful man, an optimist who loved money and believed firmly in human progress. Such men were far more common in the United States than in the Jewish circles of central Europe.”

Hence von Neumann’s emotional commitment to the atomic and hydrogen bombs and America’s Cold War against the Soviet Union – not to speak of his immunity to McCarthyite witch-hunts of Communist sympathizers. Einstein, by contrast, famously never felt at home in America, had little taste for money and deliberately avoided society in Princeton, including von Neumann’s splendid parties where guests were served by liveried footmen. Never a part of the Manhattan Project, Einstein instead suffered secret investigation by the FBI following his televised attack on the presidential decision to develop the hydrogen bomb in 1950. This revealing comparison deserves mention by Bhattacharya, who barely refers to Einstein in Princeton.

The two of them agreed in at least one key respect beyond science, however: their loathing for Nazism, and its destruction of their earlier love of Europe. Einstein refused to visit the continent after 1933. Von Neumann returned in 1949, but wrote to his wife: “I feel the opposite of nostalgia for Europe, because every corner reminds me…of the world which is gone, and the ruins of which is no solace. My second reason for disliking Europe is the memory of my total disillusionment with human decency between 1933 and September 1938.”

Von Neumann accepted that there was no “complete recipe” for avoiding human extinction by technological means

Towards the end, as cancer got hold of him and just before he received in 1956 a Medal of Freedom from President Dwight Eisenhower for his technical contributions to national defence, von Neumann asked in an article in Fortune magazine, “Can we survive technology?” The article was naturally preoccupied with the destructive potential of more powerful weapons, faster computers and more rapid telecommunications. But it presciently noted the climatic impact of rising carbon-dioxide emissions, too. Von Neumann favoured introducing new geo-engineering technologies, which he thought would unite nations more than the threat of nuclear war. Yet he accepted that there was no “complete recipe” for avoiding human extinction by technological means. “We can specify only the human qualities required,” he wrote, “patience, flexibility, intelligence.”

2021 Allen Lane £20hb 368pp

Magnetic levitation chamber could be used to simulate plant growth on Mars

A new device that uses magnetic levitation to emulate the reduced gravities found on celestial bodies such as the Moon and Mars is 1000 times larger by volume than previous systems of its kind, paving the way for more complex Earth-based tests of low-gravity environments – including growing small plants in simulated microgravity. The new simulator, which was developed at the National High Magnetic Field Laboratory (NHMFL) at Florida State University in the US, will also enable researchers to perform a variety of physics, medical and biology experiments with a view towards future space missions.

Reduced gravity affects biological organisms in many ways. It is known to inhibit cell growth, and can also cause other forms of cellular stress, leading to loss of bone and muscle mass in ways that are detrimental to astronauts’ health. In physical systems, it can affect bubble cavitation, heat transfer in fluids and the sloshing dynamics of cryogenic propellants in spacecraft. In materials research, effects of reduced gravity include changes to the way crystals grow and alloys form.

Ground-based gravity tests

The best way to find out how microgravity will affect a given system is, of course, to send it into space. Such experiments are expensive, however, and must be conducted by astronauts rather than scientists trained in that specific discipline, which limits the types of tests possible. Researchers have therefore developed several ground-based devices that exploit free fall to simulate reduced gravities, including drop towers, aircraft in parabolic flight and suborbital rockets. While useful for many types of experiment, these devices maintain low gravity for a few minutes at best, making them unsuitable for tasks that require long observation times.

Magnetic levitation-based simulators (MLS) are an alternative approach, and researchers have already used them to levitate living organisms without causing them harm. Compared to other low-gravity simulators, researchers at the FAMU-FSU College of Engineering and the NHMFL say that MLSs are cheaper, allow the exact strength of gravity to be adjusted, and offer practically unlimited operating times. The snag is that a conventional MLS can only create low gravity over a small volume. Indeed, when the simulator mimics an environment with about 1% of Earth’s gravity, g, the functional volume is only a few microlitres, which is too small for practical experiments.

Unprecedented functional volume

Researchers led by Wei Guo overcame this problem by adapting the magnet to generate a uniform levitation force that balanced the gravitational force over a much larger volume. They did this by placing a so-called gradient-field Maxwell coil (a configuration first put forward by physicist James Clark Maxwell in the 1800s for producing uniform field gradients) in the 120 mm-bore of a superconducting magnet.

The technique produced an unprecedented functional volume of over 4000 microlitres in a compact coil with a diameter of just 8 cm, explains team member Hamid Sanavandi. When the current in the MLS is reduced to emulate the gravity on Mars, which is 0.38 g, the functional volume can be greater than 20,000 microlitres, or about 20 cm³. Another advantage is that the MLS can be fabricated using existing high-temperature superconducting materials known as rare-earth barium copper oxide (REBCO), he adds.

“The fact that our MLS design offers a functional volume about three orders of magnitude larger than that for conventional solenoid MLSs makes it a potential game-changer in the low-gravity research field,” Guo says. “When this MLS design is used to emulate reduced gravities in extra-terrestrial environments, such as on the Moon or Mars, the resulting functional volume is large enough to accommodate even small plants, making this an exciting tool for medical and biology research.”

Looking ahead, the researchers, who report their work in NPJ Microgravity, say they now plan to further optimize their design by using artificial-intelligence-aided optimization methods. “We will also be securing funds to fabricate the MLS we have designed for experimental testing,” Guo tells Physics World.

Entangling a live tardigrade, radiation warning on anti-5G accessories

Tardigrades are tiny organisms that can survive extreme environments including being chilled to near absolute zero. At these temperatures quantum effects such as entanglement become dominant, so perhaps it is not surprising that a team of physicists has used a chilled tardigrade to create an entangled qubit.

According to a preprint on the arXiv server, the team cooled a tardigrade to below 10 mK and then used it as the dielectric in a capacitor that itself was part of a superconducting transmon qubit. The team says that it then entangled the qubit – tardigrade and all – with another superconducting qubit. The team then warmed up the tardigrade and brought it back to life.

To me, the big question is whether the tardigrade was alive when it was entangled. My curiosity harks back to the now outdated idea that living organisms are “too warm and wet” to partake in quantum processes. Today, scientists believe that some biological processes such as magnetic navigation and perhaps even photosynthesis rely on quantum effects such as entanglement. So perhaps it is possible that the creature was alive and entangled at the same time.

In the preprint, the researchers say that the entangled tardigrade was in a latent state of life called cryptobiosis. They say they have shown that it is “possible to do a quantum and hence a chemical study of a system, without destroying its ability to function biologically”.

Extreme record

And if that is not impressive enough, the team has set a record for the extreme conditions a complex form of life can survive. The tardigrade spent 420 hours at temperatures below 10 mK and pressures of 6×10⁻⁶ mbar and managed to survive

Tardigrades are much more resilient than humans when it comes to exposure to ionizing radiation. So they can ignore a recent announcement from the Netherlands Authority for Nuclear Safety and Radiation Protection (ANVS) warning people against wearing several items that are claimed to “protect” from the microwave radiation used by 5G networks. It turns out that some anti-5G pendants, necklaces, bracelets and sleeping masks sold in the Netherlands emit levels of ionizing radiation that could be harmful if the items are worn next to the skin for long periods of time. One of the items is designed for children.

As well as not wearing the items, the ANVS is advising people to store them in their original packaging and keep them in a closed cabinet. “Do not throw the products away with your household waste,” says the agency, adding that the items “contain radioactive materials or waste”. The agency is currently working on a plan to collect and dispose of the material.

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