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Home » Page 452

Solar radio waves could help monitor glacier thickness

Radio signals from the Sun could be used to monitor changes to ice sheets, researchers from the US have demonstrated. This new, passive radar system could offer a cheaper, lower power and more easily scalable method to gather long-term data on the melting of ice sheets and glaciers due to climate change, say the researchers.

The melting of land ice is one of the principal drivers of sea level rise, threatening coastal and low-lying communities around the globe. At present, the main way of measuring the extent of these ice sheets is to make ice-penetrating radar measurements from aircraft, using an active system to transmit a radar signal down through the ice sheet and measuring the radio waves reflected back. Airborne radar has its limitations, however, being both resource-intensive and able to provide only a snapshot of ice conditions at the time of the flight.

Low-energy monitoring

The alternative, proposed by radar engineer Sean Peters of the Massachusetts Institute of Technology (MIT) Lincoln Laboratory in the US and colleagues, instead uses naturally-occurring radio waves emitted by the Sun. The team’s sensors isolate a snippet of solar radiation in the 200–400 MHz band, then listen for that same signature in the echo created when the Sun’s radio waves bounce off the base of the underlying ice sheet – taking advantage of the randomness of the Sun’s emissions, which are, the team explain, somewhat like a song that never repeats. As with airborne radar, the delay between the original signal and the echo can then be used to calculate the distance between the surface sensor and the base.

Without the need to transmit its own signal, the team’s system is considerably less energy-intensive than its active counterparts. It could even run off batteries, potentially facilitating the creation of practical, continually-operating ice monitoring networks if the hardware can be suitably miniaturized, the team say.

“Our goal is to chart a course for the development of low-resource sensor networks that can monitor subsurface conditions on a really wide scale,” explains Peters, who conducted research for the study during his time as a graduate student at Stanford University in California, US. Such a network, he added, “could be challenging with active sensors, but this passive technique gives us the opportunity to really take advantage of low-resource implementations”.

Glacier tests

The researchers tested their approach on Store Glacier in western Greenland. There, the prototype sensor recorded an echo delay time of around 11 microseconds, which equates to an ice thickness of about 900 m — the same value recorded by ground-based and airborne active radar systems.

The concept does have limitations. One is that the level of solar radiation is relatively low, especially at the Earth’s poles. However, Hugh Griffiths, an electrical engineer from University College London, UK, who was not involved in the research, says that integrating the signal for long periods should help overcome this barrier. “The solar radiation is broadband, and in polar regions the likelihood of any interference is practically zero,” Griffiths adds.

Another drawback is that, just as active airborne systems only work during a fly-over, the passive sensor concept only works when the Sun is positioned above the horizon. The team is presently exploring whether it might be possible to harness other naturally-occurring or human-made radio sources to overcome this restriction.

Icy moon measurements

Terrestrial ice monitoring is not the only potential application for this passive radar system. The concept was originally conceived by team member and astronomer Andrew Romero-Wolf of NASA’s Jet Propulsion Laboratory as a means of probing Jupiter’s icy moons. In that application, the need for a passive system arose after it became clear that radio waves from Jupiter itself would interfere with active radar systems aboard a spacecraft — but also that the very same waves could be used to solve the problem they created.

“Monitoring ice sheets under climate change and exploring icy moons at the outer planets are both extremely low-resource environments where you really need to design elegant sensors that don’t require a lot of power,” explains team member and Stanford geophysicist Dustin Schroeder.

Electrical engineer Chris Allen of the University of Kansas, US, calls the design a “significant accomplishment that will spark other innovations in passive radar applications”. Allen, who was not involved in the work, adds: “There is no doubt that with the advent of future generations of software-defined radar technologies, the realizable spatial, spectral, and temporal resolutions will likewise improve.”

The study is described in Geophysical Research Letters.

Why these tax benefits could help you start a business

I wrote last month about the role that venture capitalists play in funding fledgling businesses. These are people who will invest cash in potentially risky but promising start-ups in return for a stake in the company. But there is a bewildering array of other options to get your new firm off the ground, including business angels, grants, loans and incubator programmes.

Another great option is to take advantage of government tax incentives. In the UK, the most useful is the Enterprise Incentive Scheme (EIS), which since 1994 has been providing tax breaks for those taking a risk on – and investing in – qualifying companies. For even earlier investments, there is the Seed Enterprise Incentive Scheme (SEIS). It was launched in 2012 with the ambitious goal to “stimulate entrepreneurship and kick start the economy”.

There is a bewildering array of other options to get your new firm off the ground, including business angels, grants, loans and incubator programmes.

SEIS applies to the first £150,000 invested in a business by outside investors, who can claim back 50% of their cash from Her Majesty’s Revenue and Customs (HMRC) via income tax relief. Even better, if the business succeeds (and the shares are sold at a profit by the investor), the investment is largely exempt from capital gains tax as well. So far over 12,000 companies have received more than £1bn of funding on which investors have received tax relief via the scheme.

As for the EIS, which is for later-stage investments into companies, it allows investors to claim back 30% of their investment via income tax relief. More than 31,000 companies have so far received investment via this scheme, raising some £22bn of funds in the process.

I’m not a financial adviser so do check out the latest official information about both schemes from the UK government website before taking any business decisions. But if you have a new firm, then as soon as you’ve finalized your first draft business plan, I would definitely encourage you to apply for advanced assurance from HMRC to confirm that the proposed investment in the company will qualify for a tax break for future investors, such as business angels.

Securing final confirmation from the HMRC can take several months, so that early assurance could be vital in persuading a would-be investor to plough cash into your business. You can, of course, apply to EIS and SEIS after an investment has been made but getting advanced assurance will reassure potential investors that they will get the tax break. In fact, they might end up investing more than planned.

Credit where credit’s due

Another consideration for a fledgling business is whether to take advantage of research and development (R&D) tax credits. These are great as they reduce the overall cost of R&D projects by allowing companies to obtain tax relief on the money spent on such work. Here in the UK, they were launched in 2000 for small- and medium-sized enterprises (SMEs), before being extended to larger companies in 2002.

In practical terms, R&D tax credits allow companies that have not made a profit in a particular year to receive money from HMRC. The cash can be crucial, especially for early-stage physics-based firms that need to spend a lot on R&D to create a product. In 2017/18 alone, tax credits provided some £5.1bn of support to nearly 60,000 British businesses. For larger and more established companies, such schemes can even influence which countries they locate R&D projects in.

Here in the UK, the government has just completed a consultation on how these schemes can be improved to encourage more investment through them. With an ambitious target to raise total investment in R&D to 2.4% of UK gross domestic product (GDP) by 2027, the government believes that R&D tax reliefs can encourage this investment by cutting the costs of innovation. The Institute of Physics (IOP) has already responded formally after consulting IOP members via its Business Innovation and Growth group.

The IOP has identified areas where the scheme could be improved to benefit physics-based businesses. In particular, there is a concern over what qualifies as R&D, which currently makes the scheme seem inaccessible to many such companies. They have to show how a project “could not be easily worked out by a professional in the field”, which naturally appears to fit with lower levels of technological readiness levels (TRL) and appears more like a patent definition.

A simpler definition of R&D would also help with the application process, which is so complicated that it has spawned an entire industry of advisers. Usually operating on a “no-win-no-fee” basis, they do a good job. But if you do succeed, you might have to pay them as much as 20% of the benefit gained – money that should be going to fund further R&D. A simplification would also encourage more firms to apply.

As the IOP has stated in its submission, a broader definition of R&D would allow firms to apply for tax credits on much later TRL development costs too. That could be a great benefit for physics-based firms, which often face big risks and costs even when building production lines. Currently those investments wouldn’t count as R&D, which has a much narrower scope.

The consultation is a great opportunity for the UK government to fine tune its R&D tax credit schemes.

Another drawback of the current scheme is that it only applies to money that has already been spent. You can only make a claim once the financial year is over, which means it can take up to 18 months (if your accounts need to be audited) to get any money back on your investment. That can be far too long for a fledgling firm, where cash flow is crucial

But I don’t want to end on a sour note. I do believe the consultation is a great opportunity for the UK government to fine tune its R&D tax credit schemes, which will help to boost the UK economy and increase the global competitiveness of British physics-based businesses. In this post-Brexit era, that’s more important than ever.

New material breaks low-thermal-conductivity record

A new inorganic material with the lowest thermal conductivity ever reported could be a boon to technologies that convert waste heat into power. The material, which conducts heat almost as poorly as air, was designed and synthesized in a way that combines two different arrangements of atoms, each of which slows down the speed at which heat moves through it.

Of all the energy generated worldwide, a staggering 70% currently goes into waste heat. As well as being bad for the environment, waste heat also causes electronic devices to overheat, decreasing their efficiency and lifespan. Some of this heat can, however, be harnessed by using materials with a low thermal conductivity κ to convert it into electricity.

Reducing heat transport via phonons

A solid’s thermal conductivity stems from the behaviour of its phonons, which are vibrations of its crystal lattice. There are two main ways to reduce heat transport via phonons: reduce the length over which the phonons scatter, or reduce the speed at which they travel as a group.

The phonon scattering length depends on the scattering between phonons themselves and the scattering of phonons by defects or boundaries within the material. The phonon group velocity, on the other hand, depends on the structure and composition of the material. Researchers have previously tried to reduce the phonon scattering length by engineering defects in materials and producing materials with nanostructures specially designed to have a low κ. Other techniques include changing the layers between crystals to alter phonon interactions at the interface between the layers.

Synergistic combinations

In the latest work, Matt Rosseinsky, Jon Alaria and colleagues at the University of Liverpool, UK, produced a composite material containing layers that selectively target phonons travelling along and across the material’s bulk. By interfacing layers of BiOCl and Bi2O2Se with Bi4O4SeCl2, they succeeded in suppressing (respectively) the contributions of longitudinal phonons and transverse phonons to the material’s total thermal conductivity. The resulting composite has a thermal conductivity of just 0.1 watts per metre Kelvin (W/m K) at room temperature along its stacking direction — among the lowest of any bulk inorganic material and only four times greater than the thermal conductivity of air.

“The starting point of the new research was to understand how the structure of a material would allow us to control heat transport through it,” Rosseinsky and Alarai explain. During their ongoing five-year-long investigation into so-called multiple anion materials, they first needed to develop new chemistry that would allow them to synthesize their material by synergistically combining two different and unusual arrangements of atoms. They also needed to identify the mechanisms responsible for reduced heat transport in each arrangement by measuring and modelling the thermal conductivities of the different structures involved.

“It is difficult to combine the mechanisms in a single material because you have to control exactly how the atoms are arranged within it,” they explain. “Intuitively, you would expect to get an average of the physical properties of the two components. By choosing favourable chemical interfaces between each of these different atomic arrangements, we experimentally synthesized a material that combines them both.”

Improved low-κ materials

Importantly, the new material has a much lower thermal conductivity at room temperature than either of the materials containing just one such arrangement. This unexpected result shows that the location of the different atoms in the structure is important, and it helps to explain why the properties of the whole are better than those its component parts.

Rosseinsky, Alaria and colleagues now hope to optimize the electronic properties of their material to create a thermoelectric. They also plan to transfer the new design principle to other classes of inorganic material that could be employed in thermal barrier coatings for gas turbines. These coatings need to have a thermal conductivity lower than that of silica glass, which has a κ of 0.9 W/m K.

According to the researchers, their strategy of combining different atomic arrangements to maximize their effectiveness in reducing heat flow has not yet reached an endpoint. “These materials could be improved even further by optimizing the arrangement of each of the structures individually before combining them,” they tell Physics World.

Full details of the research are reported in Science.

Bullying and harassment rife in astronomy and geophysics, finds poll

Astronomy and geophysics have a systemic bullying and harassment problem, the effects of which are disproportionately felt by women and individuals belonging to minority groups. That is according to an investigation by the Royal Astronomical Society (RAS), which has also found that younger researchers were more likely to be the victim of bullying than their more senior counterparts.

Commissioned by the RAS Committee on Diversity in Astronomy and Geophysics, the survey asked recipients whether they had witnessed or been subjected to workplace bullying or harassment over the last two years, if they felt their institution did enough to combat such behaviours and whether they felt treated with dignity and respect in their position.

The survey – which was distributed in spring 2020 – received 661 replies, of whom 390 reported being based in the UK, and 100 in Europe. Around half, meanwhile, were RAS members. The results revealed that 44% of respondents had been bullied or harassed at work in the previous two years – and that victims of this behaviour were found in all demographic groups analysed.

However, some demographics were worse off than others. Women and non-binary persons were around 50% more likely to be bullied than men, for example, while both disabled and black or ethnic minority individuals were 40% and 37%, more likely, respectively, to be mistreated than their non-disabled or white peers. Additionally, half of LGBTQ+ respondents reported having been bullied at least once in the previous 12 months, and 12% of bisexual astronomers reported incidents occurring on at least a weekly basis.

Feeling pushed out

Many respondents who had either witnessed or been on the receiving end of harassment wrote that they felt unable to report the incidents to their institutional authorities – with reasons cited being the power imbalance between them and their persecutor, a lack of available support, or even being dissuaded to do so by the nature of policies and structures involved.

The results from the survey are very concerning, and we must act to change this unacceptable situation

Emma Bunce

“It’s bleak – and sadly somewhat unsurprising – but this is unequivocal evidence to show we need to improve the workplace culture in academia,” says RAS diversity officer Aine O’Brien, who conducted the survey. “We have a well-reported diversity problem in [science] and this does nothing to help. Women and minorities are feeling pushed out. By shining a light like this…it means no institution or research sub-field can say ‘it doesn’t happen here’. We have a collective responsibility to address this.”

O’Brien speculates that future steps to tackle the problems could involve an inquiry into the issue, additional funding to support grassroots minority groups in the field or trying to encourage funding councils to factor bullying reports into their decision-making processes (although some have previously expressed reluctance to do this).

The team also notes that respondents on non-permanent contracts were more likely to report having been the victims of workplace harassment. Other concerning findings from the study include that most respondents with disabilities felt that they were less likely than their peers to be treated with dignity and respect at work – while 17% reported receiving bullying and harassment on a weekly basis.

As the first of its kind in these two fields, the study is unable to show whether the situation is changing, although future iterations of the survey may be able to provide a more long-term perspective. However, O’Brien notes that the results broadly mirror findings from a census last year by the Space Skills Alliance, in which women, ethnic minorities, LGBTQ+ people and those with disabilities were less likely to report feeling welcome working in the space sector.

“The results from the survey are very concerning, and we must act to change this unacceptable situation,” says RAS president Emma Bunce. “[The society] is committed to working alongside the community to urgently improve the environment in astronomy and geophysics.”

The full findings of the survey are expected to be published later this year.

Ask me anything: Mariya Lyubenova – ‘I love the constant supply of food for thought that research offers’

Mariya Lyubenova
Mariya Lyubenova

What skills do you use every day in your job?

Science is a highly creative endeavour and also requires logical problem solving, so what I use most often are my analytical skills and creativity. In both my science communication work and my research, these skills are indispensable.

Another skill that I use on a daily basis is the ability to learn fast about research in other fields and disciplines. My own scientific expertise is in the area of galaxy evolution. However, my work as a science adviser and editor of a science and technology journal confronts me with a variety of fields in astronomy and engineering, and often with other natural sciences (and sometimes even social sciences). So I need to learn quickly about those fields to understand what I’m reading.

Last, but not least, I rarely have a day in which I don’t need strong diplomacy and negotiation skills; these are very important in all areas of my work. Combined with analytical skills, they give me the ability to get to the root of a problem and find common ground, so we can reach a mutually beneficial outcome for all.

What do you like best and least about your job?

I like the variety that my job offers, and that I am working at the forefront of astronomy research. Making sure that new science results reach as broad an audience as possible is really rewarding. Due to the nature of my position, I wear several hats at once, which guarantees that I never get bored. My daily job can change completely in the course of a few hours.

My various tasks include reviewing scientific manuscripts for publication in our science and technology journal, or as a press release, or in another communication product; providing science and strategy advice to stakeholders regarding their communication activities; discussing new ways to visualize scientific concepts with our visual artists; meeting my students to ponder puzzling questions that come up in their science projects; and making progress on my own scientific research. I love the constant supply of food for thought that research offers, as well as having the opportunity to work and interact with a diverse range of colleagues in terms of expertise and cultural backgrounds.

I love the constant supply of food for thought that research offers, and working with diverse colleagues in terms of expertise and cultural backgrounds

What I don’t enjoy is the time pressure of deadlines, which can often be very tight. A key to meeting the deadlines is having good self-discipline and distributing tasks to the members of my team who are best suited to accomplishing them.

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

I wish I knew that one failure is not the end of everything. There is really no need to be absolutely perfect from the beginning in whatever you do – if you were, you would miss vital opportunities to learn from mistakes. I know this sounds a bit cliché, but I really wish I had internalized this understanding earlier. I don’t mean to promote sloppiness – quite the contrary. I have come to realize that I learn best and fastest when I am able to quickly analyse a mistake and then move on to apply what I have just learned to my next endeavour, and ultimately achieve a better result.

PET imaging tracks ingested microplastics in mice

Microplastics, tiny pieces of plastic debris less than five millimetres in length, are designed for commercial use or created through the breakdown of consumer products and industrial waste. They litter our oceans, they have been detected in everything from aquatic life to drinking water, and they take lifetimes or longer to decompose. In 2019, the World Health Organization called for more research on the effects of microplastics to the environment and human health.

Humans ingest and inhale microplastics, and they also can absorb them through the skin. Less is known about the risks and health effects of these exposures. In some animal studies, exposures to large amounts of microplastics have been associated with inflammation, metabolic disruptions, increased cancer risk and other adverse health effects.

To begin to learn more about how microplastics interact with the body, researchers in South Korea turned to functional imaging.

Tracking radiolabelled microplastics in mice

Jin Su Kim, Choong Mo Kang and their teams at the Korea Institute of Radiological & Medical Sciences and the University of Science and Technology observed and imaged mice that had ingested microplastics that were labelled, or paired, with a harmless radioactive compound.

The mice ate small plastic compounds joined to copper-64, a positron-emitting radioisotope, and DOTA, a molecule that helps bind copper-64 to plastic. For two days the researchers traced the paths taken by the tagged microplastics after they were ingested, by detecting pairs of gamma rays created during the decay of copper-64.

Positron emission tomography (PET) scans and accompanying gamma camera scans confirmed that the microplastics had spread throughout each animal’s body. Over the 48-hour observation period, the plastics passed through and were taken up by the stomach, intestines, liver, spleen, heart, lung, kidney, bladder and other organs. The researchers also observed the accumulation of radiolabelled copper-64 in tissues.

Ex vivo thin layer radio-chromatography confirmed that the small PET signals were indeed coming from radiolabelled microplastic and not another form of copper-64, and organs were identified using simultaneously acquired computed tomography (CT) scans.

What now?

The researchers’ results, which were published in the Journal of Nuclear Medicine, “may be used as the basis for future studies on the toxicity of microplastics,” says Kim, one of the senior authors on the study.

“There are many studies on the absorption of microplastics using fluorescent plastics in the body,” explains Kim. “However, we are the first to identify the in vivo absorption pathway of microplastics over time using radioisotope and PET techniques.”

The big advantage of the researchers’ PET imaging technique is that, unlike fluorescent plastics-based studies, it doesn’t require animal sacrifices at each observation time point.

The researchers’ next steps are to evaluate the biological effects of long-term exposure to microplastics in organs and continue to identify the in vivo pathways of small pieces of plastic derived from the breakdown of larger plastic debris, another type of plastic that they would like to track with PET. Major challenges for future work include labelling radioisotopes to these larger microplastics, which requires the addition of molecules not ordinarily present in plastic, and then detecting useful signals.

Twisted trilayer graphene could be a spin-triplet superconductor

Physicists in the US and Japan have observed superconductivity in a graphene-based material during the application of very high magnetic fields. What is more, the superconductivity re-emerges after dropping to zero as the field strength is increased.

The team, led by Pablo Jarillo-Herrero at the Massachusetts Institute of Technology, spotted the curious behaviour in magic-angle twisted trilayer graphene (MATTG), which is a member of a family of 2D materials that have extraordinary properties. The team’s observations suggest that MATTG displays the extremely rare property of 2D spin-triplet superconductivity – which could be used to create more resilient quantum computers.

When an electrical current is applied to a conventional superconductor, Cooper pairs of bound electrons can move through the material without any electrical resistance. Normally, these electrons exist in spin-singlet Cooper pairs, in which the electrons’ spins point in opposite directions.

Pauli limit

When a strong magnet field is applied to a superconductor, these spins are forced to both point in the same direction, thus destroying the Cooper pairs and the superconductivity. This occurs at a field strength called the Pauli limit, which in conventional superconductors is about 3 T.

In some exotic superconductors, Cooper pairs can be formed by electrons in a spin-triplet state in which both spins point in the same direction. In this case, pairs can stay bound together in magnetic fields above the Pauli limit.

Graphene is a sheet of carbon just one atom thick and Jarillo-Herrero’s team made their discovery as part of their exploration of the exotic electrical properties of stacked sheets of graphene. In 2018, the team found that if the atomic lattices of bilayer graphene are rotated slightly by a magic angle, the material becomes a superconductor. In 2021, the team found that magic angle twisted trilayer graphene (MATTG), where the atomic lattice of the middle layer is rotated slightly relative to the top and bottom layers is also a superconductor, but also appeared to be unusually resistant to high magnetic fields.

High fields

Now, the team has investigated this property of MATTG further. When applying a current to the material and measuring its resistance, they found that superconductivity only disappeared entirely at applied magnetic field strengths of around 8 T.

But that is not all. When the team further increased the strength of the magnetic field, the material became a superconductor again. Indeed, the superconductivity endured to fields as high as 10 T, which was the maximum strength of their magnet. This is 2–3 times the expected Pauli limit for MATTG.

Called re-entrant superconductivity, this effect has been seen in other spin-triplet superconductors, leading the team to suggest that MATTG is such a material – something that they hope to confirm in future studies.

Even if MATTG is not a spin-triplet superconductor, its resilience in high magnetic fields could lead to significant improvements in technologies such as magnetic resonance imaging (MRI) – which relies on superconducting magnets to create high magnetic fields. Superconductors are also used as quantum bits (qubits) in some quantum computers, and MATTG-based devices could be more resilient to debilitating magnetic noise.

The research is described in Nature.

US Nobel-prize-winning physicist Steven Weinberg dies aged 88

The US physicist Steven Weinberg, who shared the 1979 Nobel Prize for Physics for his theoretical contributions to the Standard Model of particle physics, died on 23 July aged 88. In the 1960s Weinberg’s work was instrumental in understanding the weak interaction in particle physics, which is best known for its role in nuclear decay. He shared the 1979 Nobel prize equally with Sheldon Glashow and Abdus Salam.

Born in New York on 3 May 1933, Weinberg attended the Bronx High School of Science, which has seen seven former pupils go on to win physics Nobels. In 1954 Weinberg received a degree in physics from Cornell University and after a year at the Institute for Theoretical Physics in Copenhagen (now the Niels Bohr Institute), he returned to the US to compete his PhD at Cornell University, graduating in 1957.

After a stint at Columbia University, in 1959 Weinberg went to the University of California, Berkeley, before heading to Harvard Univeristy in 1966. A year later, Weinberg became a visiting professor at the Massachusetts Institute of Technology where he carried out much of his pioneering work in unifying the weak and electromagnetic interaction.

Unifying forces

In 1967, at the age of 34, Weinberg published his groundbreaking work. Entitled “A Model of Leptons” and barely three pages long, it became a cornerstone of the Standard Model of particle physics – and one of the most highly-cited papers in physics. The work predicted the existence of the W and Z bosons, which carry the electroweak force, and also theorized that “weak neutral currents” dictated how elementary particles interact with one another.

Working independently to Weinberg, Glashow (who was in the same year group as Weinberg at the Bronx high School), and Salam made their own contributions to the model, which later became known as the Salam-Weinberg theory. However, at the time it was not taken seriously by some in the community because it seemed impossible to subject the theory to the usual “renormalisation” procedure. This meant it generated infinite and therefore meaningless expressions, so it seemed impossible to perform accurate calculations with it.

That particular issue was overcome in 1972 when the Dutch physicists Matinus Veltman and Gerardus ‘t Hooft showed how to carry out this renormalisation and used their theory to make precise calculations of particle properties. A year later and physicists working at the CERN particle-physics lab near Geneva announced the discovery of weak neutral currents — interactions that are governed by the Z boson. In 1979 Glashow, Salam and Weinberg were awarded the Nobel Prize for Physics for “for their contributions to the theory of the unified weak and electromagnetic interaction between elementary particles, including, inter alia, the prediction of the weak neutral current.” The W and Z particles were then detected for the first time in 1983 at CERN.

[Weinberg was] one of the most accomplished scientists of our age, and a particularly eloquent spokesperson for the scientific worldview

John Preskill

In 1973 Weinberg went back to Harvard where he also held a position at the Smithsonian Astrophysical Observatory. In 1982 he moved to the University of Texas at Austin, where he spent the remainder of his career. Weinberg was a vocal advocate for the proposed $4.4bn Superconducting Super Collider – a huge 87.1 km circumference circular collider to be built in Waxahachie, Texas – that failed to receive funding and was cancelled in 1993. He also had a long-time interest in nuclear proliferation and served as a consultant for the US Arms Control and Disarmament Agency.

Book and prizes

Weinberg never retired and worked in many areas of physics throughout his career. One of which was cosmology — an interest that he developed in the 1960s. Weinberg published numerous books including the popular-science account The First Three Minutes (1977), which told the story of the origin of the universe as well as Dreams of a Final Theory (1993), in which he wrote about his belief that physics was on the verge of discovering a theory that would unite physics.

One of his last books —  To Explain the World: the Discovery of Modern Science (2015) – examined the history of physics from the ancient Greeks to the present day. Yet it was criticised by some science historians and philosophers given that it judged the past from the standpoint of the present – known as “Whig interpretation”. Weinberg knew, however, that the book would ruffle feathers telling attendees at the American Physical Society meeting in Baltimore in 2016 that he was “being naughty” with the approach. He added that without the perspective of where we are now, “the story we tell has no point”.

Weinberg unlocked the mysteries of the universe for millions of people, enriching humanity’s concept of nature and our relationship to the world

Jay Hartzell

Weinberg was the recipient of numerous prizes including the National Medal of Science in 1991 and the Benjamin Franklin Medal for Distinguished Achievement in Science in 2004. Last year, he received a Special Breakthrough Prize in Fundamental physics – and with it $3m – for his contributions to physics.

A ‘colossal’ loss

Physicists have voiced their admiration for Weinberg’s work and life. John Preskill from the California Institute of Technology (Caltech), who was supervised by Weinberg as a PhD student at Harvard, says Weinberg’s death is an “immeasurable loss”. “[Weinberg was] one of the most accomplished scientists of our age, and a particularly eloquent spokesperson for the scientific worldview,” adds Preskill. “[He] remained intellectually active to the end.”

That view is backed by fellow Caltech physicist Sean Carroll who says Weinberg is one of the “best physicists we had; one of the best thinkers of any variety” who “exhibited extraordinary verve and clarity of thought through the whole stretch of a long and productive life.” Brian Greene, from Columbia Univeristy, meanwhile, says that Weinberg had an “astounding ability to see into the deep workings of nature” that “profoundly shaped” our understanding of the universe. “His passing is a colossal loss to science and the world,” adds Greene.

“Weinberg unlocked the mysteries of the universe for millions of people, enriching humanity’s concept of nature and our relationship to the world,” noted Jay Hartzell, president of the University of Texas at Austin, in a statement. “From his students to science enthusiasts, from astrophysicists to public decision makers, he made an enormous difference in our understanding. In short, he changed the world.”

The myQA SRS detector: clinical validation to clinical application in SRS/SBRT patient QA

The myQA SRS is being billed as a “game-changer” when it comes to the complex task of verifying stereotactic treatment plans in the radiation oncology clinic – enhancing treatment quality, workflow efficiency and patient safety in the process. Developed by IBA Dosimetry, a German supplier of specialist QA products and services for radiotherapy treatment centres, this next-generation 2D digital detector array is designed to support the medical physics team with patient-specific QA and commissioning of their stereotactic radiosurgery (SRS) and stereotactic body radiotherapy (SBRT) systems.

Following commercial release at the end of March, the development team at IBA Dosimetry is now focused squarely on real-world implementation, evaluation and validation of myQA SRS in the clinical setting, synthesizing inputs from a mix of early-adopting customers and beta sites. Near term, the detector’s capabilities are being road-tested by several clinics in Europe and the US, with more and more data emerging daily on the benefits of myQA SRS for patient safety and throughput within the SRS/SBRT workflow. Related abstracts have already been accepted for presentation at the virtual AAPM Annual Meeting later this month and the ESTRO 2021 Annual Congress in Madrid, Spain, at the end of August.

Innovate, evaluate, validate

Among the treatment centres putting myQA SRS through its paces is University Hospitals Bristol and Weston (UHBW) NHS Foundation Trust in the UK. Radiotherapy physicist Chris Stepanek and UHBW’s head of radiotherapy physics, Sally Fletcher, carried out their evaluation of myQA SRS on the Trust’s Elekta Versa HD linacs, using SBRT plans calculated in the RayStation v7.0 treatment planning system (TPS) for a range of beam energies and clinical indications (including spine, lung, liver and prostate).

In the clinic, the UHBW physicists integrated the detector into the cylindrical myQA SRS phantom (compatible with static and rotational delivery) or in water-equivalent Scanplas. Field and plan measurements were subsequently compared to RayStation calculations using gamma analyses, also with commissioned plan verification systems (e.g. radiochromic film and IBA Dosimetry’s CC04 ion chamber).

Operationally, the emphasis on integrated product design is key to the combined detector–phantom assembly, minimizing uncertainties in set-up, calibration and QA checks. “The detector comes with its own dedicated phantom and inserts for ion chambers and radiochromic film – all of which are straightforward to set up,” Stepanek explains. “The myQA software is also very intuitive, enhancing ease of use and efficiency within the SRS/SBRT workflow.”

Ease of use, in turn, translates into a streamlined workflow for patient-specific QA, sidestepping the lengthy and cumbersome process controls needed to get consistently accurate absolute dose data with film dosimetry. “For SRS/SBRT, QA is all about patient safety and workflow efficiency,” adds Fletcher. “As such, the myQA SRS detector will speed up time to treatment delivery for the patient, while providing reassurance that what your TPS has calculated is what your stereotactic treatment system is delivering. That reassurance is doubly important given the steep dose gradients implicit with SRS/SBRT modalities.”

A new-look QA platform

In terms of the underlying technology, the myQA SRS detector is based on a silicon complementary metal-oxide-semiconductor (CMOS) platform, which enables a compact design, fast read-out and high pixel density along the x and y coordinates (with each pixel representing a radiation-sensitive element comprising a photodiode, capacitor and three transistors). Spatial resolution is 0.4 mm, with more than 100,000 pixels across a large active area of 12×14 cm2.

myQA SRS
Workflow efficiency: IBA Dosimetry’s myQA SRS solution with the high-resolution detector (right) and advanced software (left) for streamlined SRS/SBRT patient QA measurements and plan validation.

Those specifications promise significant time savings for the QA of patients with several treatment volumes. Put simply, there is no need for the physicist to choose which targets they want to QA when everything can fit in one irradiation session to verify the complex dose distributions required for mono-isocentric SRS plans with multiple targets.

Notwithstanding the growing clinical adoption of stereotactic treatment systems, the extreme physics of SRS/SBRT – focusing high-dose radiation very precisely on a small lesion and having it fall off as quickly as possible – remains a non-trivial dosimetric and QA challenge for the radiation oncology team. In other words: it’s not easy to confirm targeting accuracy and dose-distribution accuracy when the stereotactic treatment volume can be as small as a few millimetres in diameter – and notably so for traditional QA solutions.

While film provides excellent precision in terms of dose resolution, it is cumbersome to use, time-consuming and temperamental, owing to the uncertainties in handling, calibration and development. Conversely, 2D diode arrays and ion-chamber arrays are able to generate results rapidly, though they lack the necessary spatial resolution and error-detection sensitivity for SRS/SBRT QA.

“With myQA SRS, the accuracy versus efficiency trade-off no longer applies,” claims Sandra Kos, product manager for patient QA solutions at IBA Dosimetry. “It’s that value proposition we set out to verify during our in-house evaluation of the detector in Q4 of last year and with the help of our clinical beta sites through 2021.”

Quantitative validation

The main importance, of course, is in the dosimetric detail and the ability of the myQA SRS detector to verify dose distribution accuracy in minutes rather than hours and with the necessary spatial resolution for SRS/SBRT QA. With this in mind, Stepanek, Fletcher and their UHBW colleagues used ion-chamber measurements to assess myQA SRS dose linearity, dose-rate dependence and field-size dependence, while TPS calculations and radiochromic film enabled assessment of off-axis square fields and step-and-shoot off-axis stripes.

“We validated the performance of myQA SRS through the measurement of clinical plans and subsequent comparison with small-volume ion chambers, radiochromic film and TPS doses,” explains Stepanek. “The project also evaluated the detector versus a variety of errors simulated within a selection of treatment plans, focusing in the main on sensitivity to single MLC position errors as well as gantry and collimator miscalibrations.”

Stepanek, for his part, will present full results of the UHBW study at ESTRO 2021 next month. In summary, though, the detector demonstrated good dose linearity and good dose-rate independence above 200 MU/min. Measurements of field-size dependence agreed well with small-volume ionization chambers, as did measurements of small off-axis fields versus TPS doses. Further investigations included the measurement of 6 MV and 6 MV FFF clinical plans with the detector integrated into the myQA SRS phantom. Those results also demonstrated excellent agreement versus TPS doses, ion-chamber readings and radiochromic film.

Into the clinical workflow

Through the second half of this year, the UHBW medical physics team will continue its clinical evaluation of myQA SRS, while Kos and her colleagues are focused on collating feedback from customers and various beta sites to inform the next phase of myQA SRS product development.

“Right now,” Kos adds, “the detector is validated and released for standard C-arm linacs capable of delivering stereotactic treatments, though we already have further clinics working on operational validation of the detector with different treatment delivery machines.”

AAPM meeting highlights the creativity of science and innovation

This year’s Annual Meeting of the American Association of Physicists in Medicine will exploit a new online platform to enable a global audience of medical physicists to share ideas, interact with colleagues, and learn about innovative products. The virtual meeting will take place on 25–29 July, providing five days of real-time scientific, professional and educational content, while an on-demand option is also available for registrants to catch up on anything they missed during that five-day period.

The theme for this year’s meeting is “Creative science. Advancing medicine”. According to the AAPM president, James T Dobbins III of Duke University, the meeting will explore the ways in which medical physicists can use their creativity and scientific expertise to build the clinical practice of the future. The Presidential Symposium will focus on the topic of creativity in science, and Dobbins says that the meeting sessions “will explore our roles as scientific innovators in both research and the clinic”.

Once again the meeting will feature a virtual exhibit hall, which proved to be a real success in 2020. Included in the conference programme is a track of vendor showcases, which enable companies to host demonstrations of their latest products. Delegates can also interact with a selection of vendors through a series of “Partners in Solutions” sessions, which are designed to provide clinical physicists with practical information on using specific systems.

Meanwhile, exhibitors have the opportunity to host guided tours of their virtual booth to highlight products designed to address specific clinical needs, as chosen by the organizing committee. Some of the innovations that vendors will be introducing, particularly for fast and accurate quality assurance (QA), are highlighted below.

Zeus phantom puts MR-guided linacs to the test

The Zeus phantom from CIRS combines an MR-safe motion-control platform with an MR-realistic body to provide complete end-to-end testing of MR-guided linac systems such as ViewRay’s MRIdian and Elekta’s Unity.

The phantom’s gel-filled body contains anthropomorphic lungs, liver, kidney and spine with a life-like shape and spatial relationship, and offers imaging contrast in both MR and CT. MR-safe piezoelectric motors move a cylindrical insert with an organic-shaped tumour through the phantom body in three dimensions. All organs except for the lungs offer ion-chamber dosimetry cavities for completing an entire QA process.

Zeus phantom
The Zeus phantom from CIRS provides end-to-end testing of MR-guided radiotherapy systems. (Courtesy: CIRS)

The phantom is equipped with motion-control software that includes multiple built-in profiles for use during commissioning and for routine QA. It also allows patient-specific respiratory waveforms to be imported and, if needed, to be edited for amplitude, sample rate, cycle time, phase shift and baseline position.

The software allows users to set up independently controllable waveforms for both linear and rotational motion of the insert, while the inferior–superior motion of the insert or moving target can be gated based on amplitude to verify the beam latency of the machine. Finally, a physical interface for the beam-on/beam-off signal can be read by the motion control software to calculate the beam latency specific to hybrid MR-linac systems.

3D measurement of MR image distortion achieves sub-millimetre precision

A new distortion-analysis system from Modus QA offers a lighter, larger and more efficient way to quantify the geometric distortions in MR imaging in three dimensions. Measuring these distortions and establishing accepted thresholds is crucial for achieving accuracy in MR-guided radiotherapy treatments, and the QUASAR MRID3D delivers sub-millimetre accuracy for commissioning and continuous QA of MR-guided systems.

An efficient workflow is enabled by a hollow-boundary phantom design with a large field of view (37 x 32 cm2), which allows set-up, scan and analysis in less than 10 minutes. In addition to automated distortion quantification, the phantom software also offers advanced features to correct any errors that arise from phantom susceptibility distortions, the spherical harmonics coefficient output, any rotation or movement of the patient table, and inhomogeneities in the magnetic field and the gradient nonlinearity. Image analysis software provides a built-in 3D DICOM viewer and region-of-interest selector, allowing users to analyse smaller custom volumes.

Modus white paper
A new white paper from Modus QA explores the factors that affect MRI geometric image distortion, as well as the tools that can be used to quantify it. (Courtesy: Modus QA)

Modus QA has released a white paper that reviews the factors that affect MRI geometric image distortion, as well as the tools that can be used to quantify it. It also explores the spherical harmonic analysis approach exploited in the QUASAR MRID3D, and presents the recommended method for measuring a full 3D distortion vector field with this large field-of-view phantom.

Updated software expands capabilities for machine QA

Sun Nuclear’s SunCHECK platform, which is widely used to standardize both machine QA and patient QA among staff, sites and equipment, offers more than 50 feature enhancements in its latest release. Among other things, version 3.2 of the software improves task and template customization, expands support for imaging tasks, and makes it easier to share templates.

SRS MapCHECK
SRS MapCHECK is the only device that offers both machine QA and patient QA on a CyberKnife system. (Courtesy: Sun Nuclear)

Sun Nuclear will be showcasing the latest capabilities of the SunCHECK platform in a vendor showcase session during AAPM (10.30 am EDT, Wednesday 28 July).

The company is also releasing a new version of its SNC Patient software, which is designed to provide efficient, device-specific workflows for clinical users. Version 8.5 enables SRS MapCHECK, Sun Nuclear’s film-less solution for stereotactic patient QA, to support machine QA for the CyberKnife system – which makes SRS MapCHECK the only device that offers both machine QA and patient QA on a CyberKnife.

Other new capabilities include QA for multileaf collimators, iris beams and targeting accuracy, while the new release also extends compatibility for a range of Varian and Accuray treatment delivery systems.

Another vendor showcase by Sun Nuclear offers a preview of the new features now included in SNC Patient software (10.30 am EDT, Monday 26 July).

Digital QA solution delivers speed and film-class resolution for stereotactic treatments

IBA Dosimetry will be introducing a fully digital solution for high-resolution QA for both stereotactic radiosurgery (SRS) and stereotactic body radiation therapy (SBRT). The myQA SRS system features a digital detector array for faster QA, and also achieves a film-class resolution of 0.4 mm. With an active detector area measuring 12×14 cm2, the solution offers more than 100,000 measurement pixels, while zero pixel spacing avoids the need for interpolation. The plan delivery and validation are completed in just a few minutes, making myQA SRS as efficient as any routine QA.

myQA SRS
The myQA SRS solution from IBA Dosimetry delivers fast and precise patient-specific QA for stereotactic treatments. (Courtesy: IBA Dosimetry)

“The digital detector QA workflow with myQA SRS is 106 times faster and easier compared to using film,” comments Yun Yang of Rhode Island Hospital in the US, who has tested the solution in a clinical setting. “The film-equivalent resolution for our QA measurements is the basis for better and more meaningful SRS patient plan verification with a high sensitivity and specificity to detect the real dose errors.” Yang will share his results in an AAPM presentation and a webinar that is available on the IBA Dosimetry website.

IBA Dosimetry will also be showcasing myQA iON, a software environment that combines all patient QA tasks and workflow steps in a single interface. The software allows irradiation log files and dose measurements to be used alongside Monte Carlo prediction techniques, allowing the dose profile to be recalculated with fewer measurements and greater accuracy.

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