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Colliding galaxies created the solar system, say astronomers

The solar system may have been formed in a long-ago collision between the Milky Way and its orbiting companion the Sagittarius dwarf galaxy. That is the conclusion of astrophysicists in Spain, who have analysed data from the Gaia space observatory. This cosmic “fender bender” – which occurred as Sagittarius’ orbit plunged it through the plane of our galaxy – helped to concentrate cosmic dust in and usher in a period of heightened star formation.

First identified as a satellite galaxy of the Milky Way in 1994, the Sagittarius Dwarf Spheroidal Galaxy is around one tenth of the diameter of the Milky Way. Made up of four main globular clusters of stars, our elliptical-shaped neighbour is spiralling around our galaxy on a polar orbit about 50,000 light-years from the galactic core. This brought the galaxy through the plane of the Milky Way several times in the past. Some researchers have even suggested that these collisions over the past six billion years helped to create the Milky Way’s trademark spiral structure.

“It is known from existing models that Sagittarius fell into the Milky Way three times – first about five or six billion years ago, then about two billion years ago, and finally one billion years ago,” says team member and astrophysicist Tomás Ruiz-Lara of the Instituto de Astrofísica de Canarias (IAC) in Tenerife.

Luminosities and colours

In their study, Ruiz-Lara and colleagues used data from the European Space Agency’s Gaia telescope to examine the luminosities and colours of the stars that lie within around 6500 light-years of the Sun, as to determine the star formation history of our stellar neighbourhood. They then compared this with existing models of stellar evolution.

The researchers identified three periods in galactic history where star formation appeared to occur at an increased rate — peaking at around 5.7, 1.9 and 1 billion years ago. This corresponds broadly to the times at which the Sagittarius galaxy is believed to have been passing directly through the Milky Way’s disc.

“At the beginning you have a galaxy, the Milky Way, which is relatively quiet. After an initial violent epoch of star formation, partly triggered by an earlier merger […] the Milky Way had reached a balanced state in which stars were forming steadily,” explains Ruiz-Lara. The effect of Sagittarius falling into the Milky Way, he added, was to “disrupt the equilibrium, causing all the previously still gas and dust inside the larger galaxy to slosh around like ripples on water.”

Concentrating dust and gas

The effect of these so-called ripples would have been to concentrate dust and gas in certain areas of the galaxy — promoting the more rapid formation of new stars as gravity pulled the material together. At the same time, the collisions also act to strip Sagittarius of some of its gas and dust.

Team member and IAC astrophysicist Carme Gallart observes, “It seems that not only did Sagittarius shape the structure and influenced the dynamics of how stars are moving in the Milky Way, it has also led to [its] build-up”. Without these recurring collisions with the dwarf galaxy, she adds, part of the Milky Way’s stellar mass may not have come to exist – at least, not in the form with which we are familiar – and such may have even included our very own solar system.

The Sagittarius effect

“The Sun formed at the time when stars were forming in the Milky Way because of the first passage of Sagittarius,” explains Gallart. “We don’t know if the particular cloud of gas and dust that turned into the Sun collapsed because of the effects of Sagittarius or not. But it is a possible scenario because the age of the Sun is consistent with a star formed as a result of the Sagittarius effect.”

According to ESA Gaia project scientist Timo Prusti – who was not directly involved in the analysis – such detailed insights into the Milky Way’s history would not have been possible before the Gaia observatory’s first data release in 2016.

“Some determinations of star formation history in the Milky Way existed before, based on data from ESA’s early 1990s Hipparcos mission,” he explained, adding: “But these observations were focused on the immediate neighbourhood of the Sun. It wasn’t really representative and so it couldn’t uncover those bursts in star formation that we see now.”

“This is really the first time that we see a detailed star formation history of the Milky Way. It’s a testament to the scientific power of Gaia that we have seen manifest again and again in countless ground-breaking studies in a period of only a couple of years.”

The research is described in Nature Astronomy.

Hydrogel helps make self-cooling solar panels

Moisture harvested from the atmosphere at night by a hydrogel can be used to cool down solar panels during the day, boosting their efficiency. So say researchers at the King Abdullah University of Science and Technology (KAUST) in Saudi Arabia and the Hong Kong Polytechnic University (PolyU) who made the hydrogel from a mix of carbon nanotubes in polymers with a hygroscopic calcium chloride salt. The technology could be an environmentally friendly way to increase photovoltaic electricity generation and also cool down other devices.

Solar photovoltaic (PV) panels currently produce more than 600 GW of the world’s power, and this figure is expected to increase to 1500 GW by 2025 and 3000 GW by 2030. While solar energy is an abundant, inexhaustible and very clean energy resource, commercial silicon-based PV cells can only convert between 6–25% of absorbed sunlight into electric current. The rest is transformed into waste heat, which increases the temperature of a solar panel by up to 40 °C. This makes the cells less efficient, and it can also damage them – especially in hot climates, where the problem is even more serious than in more temperate areas.

Current technologies to cool PV panels include refrigeration or air conditioning, but these can be energy-hungry. Water-cooling systems also exist, but they require abundant water supplies, as well as storage tanks and a complicated network of pipes and pumps.

A gel-like material with a high affinity for water molecules

A team of researchers led by Peng Wang of KAUST’s Water Desalination and Reuse Center and the Department of Civil and Environmental Engineering at PolyU recently developed an alternative cooling method. Their technique is based on a gel-like material that comprises heat-absorbing carbon nanotubes (CNTs) embedded in a cross-linked polyacrylamide (PAM) and calcium chloride (CaCl2). This gel has a high affinity for water molecules and can therefore take up large quantities of water vapour from ambient air. According to lead author Renyuan Li, the gel also has the ability to self-adhere to numerous surfaces, including solar panels, through strong hydrogen bonding.

In their experiments, the researchers pressed a 1-cm-thick layer of the hydrogel against the underside of a standard silicon solar panel. When the temperature drops in the evening and overnight, the water absorbed by the material condenses to form liquid water, explains Wang. During the daytime, as the temperature increases, the heat from the PV panel causes the water to evaporate – a process that not only removes heat from the panel, but also regenerates the vapour sorbent so that the atmospheric water harvester (AWH) is ready for the next night-day cycle.

Experiments by the KAUST-PolyU team on PV panels in the laboratory showed that a fully-engorged gel could free enough water to produce a cooling power of 295 W/m2 under 1000 W/m2 solar radiation and reduce the temperature of the panel by 10 °C. This reduced temperature improves the panel’s efficiency enough to boost the amount of electric current produce by an average of 15%. When the team tested the system on an outdoor prototype during winter and summer months on the KAUST campus, this figure increased to 19% – probably because wind enhanced the cooling effect, the researchers say.

With global PV capacity expected to reach 1500 GW by 2025, the researchers calculate that cooling all these panels using their approach would generate more than 150 GW of additional power. This boost to the electricity supply would translate into a reduction of 8.52 × 107 metric tonnes of coal consumed per year, and a drop in CO2 emissions of more than 1.48× 108 metric tonnes per year (assuming 20% solar PV electricity generation efficiency).

Improving water vapour sorption-desorption kinetics

Wang and colleagues, who report their work in Nature Sustainability, are now working to improve the corrosion resistance of their atmospheric water harvester (AWH) and increase its water vapour sorption-desorption kinetics (and thus its capacity). They are also investigating better ways of dealing with dust on PV panels – a particular problem in arid and semi-arid regions, where particles deposited by frequent dust storms can reduce the power output of a solar panel by as much 20% if not removed. One design option for the AWH cooling here, Wang says, would be to use the system to trap and condense water after it has evaporated from the hydrogel. This water could not only be used to remove any dust build up on the PV panels, it might even be clean enough to drink.

On another positive note, the technology could easily be adapted to different scales, Li adds. “It could be made as small as several millimetres for cooling down electronic devices, hundreds of square metres for a building, or even larger for passive cooling of industrial-sized PV farms.”

The researchers say they will now be testing the long-term stability of their AWH. “Our long-term goal is to demonstrate its commercial value and make it market-competitive,” Wang tells Physics World.

Nonlinear integrated photonics speeds up coherent lidar

In today’s fast-changing world, we are continuously upgrading our existing technologies and developing new ones. Yet, the basis of many breakthrough technologies lies in fundamental principles of physics. One example is the Doppler effect, which states that the frequency of a wave changes when its source is in motion relative to an observer. A car engine, for example, sounds different depending upon whether it is approaching us or receding. Likewise, light from an astronomical object moving toward us appears blue-shifted, while light is red-shifted from an object moving away.

The Doppler effect also plays a key role in coherent ranging, a technique being developed for long-range three-dimensional detection of distance and speed in autonomous driving. Coherent ranging, also known as frequency-modulated continuous-wave (FMCW) laser-based light detection and ranging (lidar), works by measuring the Doppler shift of reflected laser light coherently, thus preventing interference from sunlight and other lidar systems.

Coherent detection enhances the distance resolution, which is a critical factor in autonomous driving. But improvements often come at a cost. Coherent ranging results in a low acquisition speed and requires a highly coherent, as well as precisely chirped, laser source. Another major barrier to overcome is the technical capability to precisely control the many narrow-linewidth frequency-agile lasers used in parallel FMCW lidar.

A massively parallel coherent lidar scheme

To address this obstacle, a group of researchers led by Tobias Kippenberg at EPFL has developed a novel way to implement parallel FMCW lidar. Their approach, published in Nature, multiplexes a single FMCW laser using a high-quality silicon-nitride microresonator on a photonic chip. This frequency-modulated pump laser generates a soliton microcomb on the photonic chip. Basically, the continuous-wave laser light is converted into a stable optical pulse train, due to the double balance of dispersion and nonlinearity effects.

EPFL researchers
EPFL researchers (left to right): Johann Riemensberger, Anton Lukashchuk and Tobias Kippenberg.

In a soliton microcomb, multiple comb teeth reconstitute the equidistant optical frequency components from a single pump laser. In other words, each individual comb tooth serves as a source of frequency-modulated laser light and, channel-by-channel, recovers and reconstructs the reflected laser signal. Frequency comb generation based on dispersive spreading, for example using an optical grating, results in illumination of multiple pixels on the photonic chip and consequently can map the distance and velocity of multiple target objects simultaneously.

The technique has potential to greatly enhance the frame rate of imaging in coherent lidar systems via parallelization of ranging and detection. More importantly, this parallel architecture retains the advantages of continuous-wave operation, such as the avoidance of high peak powers. It is also inherently more eye-safe than contemporary time-of-flight-based lidar systems.

“Parallel detection, using arrays of lasers and photodetectors, was a key step in the development from 2D laser scan sensors to the 3D imaging systems that support the autonomous driving revolution,” says first author Johann Riemensberger. “Our technology can extend this principle for superior coherent detection lidar systems, while avoiding the technical challenges of operating large arrays of complex frequency-agile laser systems.”

Elekta Unity: the win-win of learning through collaboration

The Elekta Unity MR-Linac is in the vanguard of a new generation of MR-guided radiotherapy (MR/RT) systems that enable clinicians to visualize a tumour target, as well as its surrounding anatomy, with exceptional soft-tissue contrast both prior to and during treatment. Those capabilities are now poised to transform workflows in the radiation oncology clinic, delivering resource efficiencies and improving patient outcomes in the process.

It’s a compelling picture, one in which MR/RT points the way to personalized medicine tailored to the unique requirements of each patient – adjusting radiation delivery to address the daily variation in the tumour and surrounding healthy tissue, while enabling the clinician to adapt the plan for tumours that respond rapidly to treatment, as well as those that prove unresponsive to standard doses of radiation. Furthermore, that ability to capture the tumour and its environment “on the fly” will, in turn, make it possible to increase the radiation dose to diseased tissue in real-time without damaging adjacent organs at risk and other critical structures.

Among the early-adopting clinical customers for Elekta Unity is the US-based Allegheny Health Network (AHN), which is currently putting the finishing touches to a new $100 million academic cancer centre at Allegheny General Hospital (AGH) in Pittsburgh, Pennsylvania. This integrated cancer clinic will begin patient treatments later this summer using an array of cutting-edge radiotherapy systems, including the Elekta Unity MR-Linac and two additional Elekta machines (an Elekta Versa HD with onboard imaging and robotic table; also a Leksell Gamma Knife Icon with cone-beam CT and motion management).

Work in progress

Right now, the MR-Linac is still under construction at AGH, with the Covid disruption forcing the launch schedule back a couple of months. “Hopefully we’ll be moving into commissioning for the Unity over the next few weeks and are pushing for initial patient treatments in late September or early October,” explains Tom Colonias, a radiation oncologist at AGH and clinical lead on the hospital’s Elekta Unity project.

In the meantime, there’s a comprehensive training and applications programme in place so that Colonias and his colleagues are ready, from day one, to exploit Unity to the full. A case in point is the system’s on-board MR imaging capability. “We use MR scans all the time in radiation oncology,” says Colonias, “but we don’t perform the scans – they’re done in radiology. As a result, the whole department has to be MR-trained regarding the health and safety aspects of working in a magnetic-field environment.” To provide a focal point for that expertise, AGH is putting three of its radiation therapists through MR certification so that they can run the MR scanner on a day-to-day basis (although such certification is not mandatory for Unity).

Elekta’s engineering and physics teams are also working closely with AGH medical physicists to implement a rigorous and standardized approach to system acceptance, commissioning and quality assurance (QA). “We’ll be using specialized MR-safe phantoms for the commissioning QA,” says Colonias, “as well as recruiting volunteers so that we can verify the performance of the MR scanner on real people.” What’s more, all of the QA techniques and equipment for the Unity are developed to be MR-safe – from end-to-end workflow tests utilizing both the linac and MRI components of the system to patient-specific QA for each adapted plan of treatment.

In the run-up to the Unity system going live, AGH’s multidisciplinary clinical team will make recommendations on initial patient selection. On a practical level, it’s likely they will kick things off with prostate treatments and pelvic malignancies (as in each case there’s no significant organ motion and there are plenty of patients available). “It’s going to be a learning curve at the outset, getting the Unity workflow defined and really efficient,” explains Colonias. “Within six months of being operational, though, we aim to be doing real-time adaptive planning and treating up to 10 patients a day.”

Longer term, the adaptive capabilities of Unity will enable AGH to address the inherent complexities of a wide range of disease indications (see “The AHN roadmap for MR/RT”, below). Between treatment sessions, for example, patients can gain or lose weight; their stomach, bladder and bowel contents change; their organs may shift, rotate or deform; and their tumours may shrink, move or rotate. With this in mind, AGH clinicians are already planning MR-Linac studies of liver stereotactic body radiotherapy (SBRT) and pancreas SBRT, alongside a specific interest in exploring stereotactic ablative radiotherapy (SABR) to treat ventricular tachycardia (a potentially fatal condition in which the heart beats at more than 100 beats/min).

Another priority is head-and-neck cancer. “Owing to potential weight loss and tumour response during therapy, head-and-neck cancer patients can be ideal candidates for the adaptive planning afforded by the Unity,” notes Colonias. “Such adaptive treatments may result in better functional outcomes and improved quality-of-life post-treatment.”

Collaborate and accumulate

More broadly, membership of Elekta’s MR-Linac Consortium has been fundamental to the MR/RT learning experience for Colonias and his colleagues. One aspect of the Consortium is a knowledge-transfer programme that brings together more than 35 clinical institutions – all of them Elekta Unity customers – as part of a collective conversation focused on driving improved patient outcomes through the application of MR-Linac technology.

Tom Colonias
Tom Colonias: “The MR-Linac Consortium is a great vehicle for us to talk, collaborate and learn along the way with other clinical institutions.”

AHN has been involved with the Consortium for a couple of years, taking advantage of the regular international meetings to fast-track the training of its radiation oncology team on all aspects of Unity best practice – from treatment planning and MR safety to QA protocols and online adaptive workflows. “We’re starting out-of-the-box here at AHN with a new way to treat patients,” says Colonias. “As such, the Consortium is a great vehicle for us to talk, collaborate and learn along the way with other clinical institutions.”

What’s notable, Colonias adds, is that the Consortium is set up as an independent entity, with Elekta “creating the conditions” for collaboration rather than opting for top-down micromanagement. “Elekta plays an integral role in the Consortium and acts as a facilitator, letting the clinical community define priorities and share their clinical and technical outcomes,” he explains. “Of course, the Elekta product development and engineering teams are also front-and-centre, providing specialist support and training as well as gathering feedback direct from the clinical end-users.”

Down the line, the AHN team plans to work with other Consortium members on multicentre MR-Linac clinical studies – including the application of Unity’s functional MR imaging capabilities. “We get scale when we collaborate, share and analyse our study data together,” Colonias concludes. “If we have multiple Unity clinics contributing MR data on, for example, 100+ patients with pancreatic cancer [versus fewer patients as individual institutions], we can compare post-treatment outcomes and hopefully draw robust conclusions on best practice and treatment efficacy.”

The AHN roadmap for MR/RT

Multidisciplinary AHN teams have been participating in the Elekta MR-Linac Consortium meetings since September 2018, with many AHN staff (physicians and physicists) taking a prominent role within the consortium’s specialist tumour-site groups (TSGs) and brainstorming initiatives. As a result of that engagement, AHN will be contributing to multicentre clinical studies and data/outcome analysis in the following areas.

Pancreatic SBRT

  • There’s emerging evidence that radiation dose escalation provides improved outcomes for locally advanced, unresectable pancreatic cancer
  • Project driver: targeting will be easier and more reliable using Unity’s on-board MR imaging, with potential for dose escalation across 5–15 fractions (depending on surrounding structures)
  • A treatment protocol is currently being developed by the MR-Linac Consortium’s pancreatic TSG
  • AHN clinical lead: Rodney Wegner MD

Liver SBRT

  • Project driver: application of adaptive stereotactic radiotherapy for primary and metastatic hepatic malignancies
  • The study will exploit superparamagnetic iron-oxide nanoparticles (SPION) and on-board MR imaging for avoidance of healthy liver tissue (hepatic parenchyma) during 3D conformal treatment planning
  • Subsequently, MR-Linac imaging will examine the dose–response of tumour sites and hepatic parenchyma to SBRT
  • AHN clinical lead: Alexander Kirichenko MD

SABR for refractory ventricular tachycardia

  • MR is a superior imaging modality (versus CT) for visualizing the heart in terms of image planning and guidance
  • This study will evaluate the Unity platform’s “marriage of MRI-based cardiac planning and treatment delivery via radioablation”
  • The goal is MR imaging, real-time planning and treatment delivery to address tachycardia in one session
  • AHN clinical lead: Mark Trombetta MD

Supercurrent goes to the edge

Researchers at Princeton University in the US have become the first to observe a robust supercurrent at the edge of a superconductor that is very different to the supercurrent in the material’s bulk. This “topological superconductivity” could come in useful for a host of new applications, they say.

Topological materials are materials that have very different properties at the surface compared to those in their bulk thanks to special topologically protected “edge states”. Topological insulators – materials that act as insulators in their interior but conduct currents on their surface – have been a hot topic in condensed-matter research for several years, but their superconducting counterparts are less well-studied.

To find out what happens when the interior of a topological material is not an insulator but a superconductor, Nai Phuan Ong and colleagues turned their attention to molybdenum ditelluride (MoTe2). This material is a Weyl semimetal, a recently discovered class of topological material in which electrons (which are fermions, and thus have spin-1/2) behave as if they have no mass. These oddly-behaved particles were predicted in 1929 by theoretical physicist Herman Weyl as a solution to the Dirac equation (which describes the physics of normal fermions), and they travel faster and dissipate less energy than electrons in ordinary metals or semiconductors. They also show the “chiral magnetic effect” when placed in a magnetic field, which generates a current of positive and negative Weyl particles that move parallel and antiparallel to the field.

Saw-tooth pattern in critical current oscillations

The researchers began by preparing slivers of crystals of MoTe2 that were between 60 to 120 nm thick. They then cooled these crystalline samples down to below 100 millikelvin – the superconducting transition temperature of MoTe2. Next, they applied a weak magnetic field to the samples while measuring the current flow through them.

The Princeton team observed a quantity known as the critical current oscillating in a saw-tooth pattern as they increase the applied magnetic field. Both the height and frequency of these oscillations fit well with predictions of how these fluctuations arise from the quantum behaviour of electrons confined to the edges of the material, they say.

In superconducting materials, electrons overcome their mutual electrostatic repulsion to form Cooper pairs thanks to interactions between the electrons and vibrations of the material’s crystalline lattice. Once formed, these pairs behave as bosons, which have an integer spin. This means they can condense to form a “superfluid” state that behaves as a single entity, carrying electrical current through the material with no resistance at temperatures below the material’s transition temperature.

Superfluid velocity adjusts

In MoTe2 and other Weyl semimetals, this Cooper-pairing of electrons in the bulk also appears to induce a similar pairing on the edges, says Ong. The saw-tooth pattern in the critical current as the applied magnetic field increases would come from the fact that the superfluid velocity adjusts to maintain an integer number of overall twists in the phase of the superconductor’s wave function, he explains.

While he and his colleagues say they do not yet fully understand the reason for why the edge supercurrent remains independent of bulk supercurrent, they believe it could come from the topologically protected edge states in MoTe2. To find out whether this is true, they plan to repeat their experiment on other unconventional superconductors and search for similar edge supercurrents.

Although conventional superconductors are already widely employed in areas like magnetic resonance imaging (MRI) and long-distance transmission lines, new types of superconductivity like this one could help us move beyond the limitations of familiar superconducting technologies, Ong says.

The paper, entitled “Evidence for an edge supercurrent in the Weyl superconductor MoTe2” is published in Science.

Why ultrafast is ultra-good for medical imaging, helping children learn physics at home, the Cheerios effect

This episode of the Physics World Weekly podcast features an interview with Charalampos (Harry) Tsoumpas at the University of Leeds, who explains why the development of ultrafast gamma-ray detectors could be a boon for medical imaging.

Also appearing this week is the soft-matter physicist Carmen Lee at McMaster University, who talks about an online programme called Ask A Scientist that answers questions about physics from school children who are learning at home. Lee also chats about her research into the Cheerios effect.

Introducing the RadCalc 7.1 3D platform

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Participants in this webinar will learn how RadCalc’s 3D platform can improve efficiency, accuracy, and safety in the QA process for treatment plans.

The webinar, presented by Dana Cooper, will give the audience information on:

  • The workflow of the 3D platform.
  • Commissioning process and analysis tools.
  • Most popular benefits of using RadCalc 7.1.

Dana CooperDana Cooper is a certified medical dosimetrist/technical sales representative with LifeLine Software, Inc, part of the LAP Group. She has more than 25 years of experience in radiation oncology, having held positions such as radiation therapist, dosimetrist and department manager. Dana joined LSI in 2016 and has been connecting radiation therapy departments with software that increases productivity and safety ever since.

More evidence for a ‘fifth force’ found in radioactive decay measurements

Anomalies in the radioactive decay of beryllium-8 and helium-4 point to the existence of a new force of nature. That is the conclusion of a group of theorists in the US, who have scrutinized data from experiments carried out by nuclear physicists in Hungary over the past five years. Results from the two different isotopes agree on both the mass and interaction strength of the hypothetical boson that would carry the long-sought fifth force, the team found.

The Standard Model of particle physics tells us that matter particles interact with one another via four forces: electromagnetic; strong; weak; and gravity. But theorists have long hypothesized the existence of other forces, including “dark photons” that might mediate interactions between particles of dark and ordinary matter.

It was just such a particle that Attila Krasznahorkay of the Institute of Nuclear Research (ATOMKI) in Hungary and colleagues were hunting when carrying out experiments on beryllium. As they reported in a little-noticed paper in 2015, they fired protons at targets made from lithium-7 to create nuclei of beryllium-8. They then measured the angles between the trajectories of each electron and positron given off in the subsequent decays of the unstable beryllium isotope.

Mystery particle

If the Standard Model correctly describes such decays, the number of emitted electron-positron pairs should gradually drop off as the angle between the two particles increases. But Krasznahorkay and colleagues instead found an increase, or bump, in the distribution at an angle of about 140°. They interpreted this as due to beryllium-8 decaying to a previously unknown particle in a tiny fraction of its decays (before that particle then disintegrates into an electron and positron), calculating the mass of the new particle to be about 17 MeV/c2.

It was only a year later when Jonathan Feng and colleagues at the University of California, Irvine, published a theoretical analysis of Krasznahorkay’s team’s results that others took notice. Feng’s group concluded that the particle in question, if it exists, is not a dark photon but what they called a “protophobic” gauge boson – a force carrying particle that interacts more readily with electrons and neutrons than it does protons.

For other theorists, such unusual interactions cast doubt on the claimed discovery. More importantly, no other experimental group has since reproduced the anomalous results. In fact, the NA64 experiment at the CERN laboratory in Switzerland has narrowed down the range of such a particle’s possible interaction strengths by looking for evidence of its coupling to electrons and finding nothing.

Similar bump

Undeterred, Krasznahorkay and colleagues have pressed on. They rebuilt their detector between 2017 and 2018, and found that the bump at 140° remains. More strikingly, they found a similar bump at 115° in the decay of helium-4. Remarkably, they calculated that the particle responsible for this anomaly would also have a mass of about 17 MeV/c2.

That result was reported in autumn 2019 via a preprint on arXiv and prompted sensationalist headlines declaring that a Nobel prize might be in the offing. However, Feng realized that more could be done to establish whether the latest data really do stack up consistently against the old. In a new preprint, also on arXiv, he and a couple of theorist colleagues at Irvine, Chris Verhaaren and Tim Tait, not only check whether the two results agree on the mass of a putative new boson but also calculate what the particle’s interaction strength would be in each case.

Feng, Tait and Verhaaren point out that beryllium-8 and helium-4 decay at similar rates within the two experiments. But they say that that does not necessarily imply similar interaction strengths between the new boson and the quarks in each nucleus, noting that the excited states in each case have different quantum numbers and different excitation energies. They add that the beryllium-8 measurement was done on resonance while that of helium-4 was carried out between two resonances.

Remarkable agreement

After factoring all these things in, the trio concluded that the new particle does indeed interact with the same strength in both cases. Specifically, they find that the helium-4 decay rate calculated using the properties of the protophobic boson from their analysis of the beryllium-8 data agrees with the rate from the helium data. What is more, they say that such close agreement is not possible with any other type of hypothetical force carrier. “For other new particles proposed to explain the beryllium data, the predicted helium rate can be orders of magnitude off,” says Feng. “So, this concordance is, frankly, remarkable.”

To settle the issue once and for all, Feng and colleagues say that other experimentalists must try to reproduce the results. But they also propose several new measurements that could provide additional confirmation. Requiring only simple modifications of the existing experimental set-up, these include gathering data to better understand background processes as well as measuring decays from carbon-12 – whose rate they predict precisely. “If the predictions are confirrmed, these measurements will provide overwhelming evidence that a fifth force has been discovered,” they write.

Other theorists welcome the new analysis. Rouven Essig of Stony Brook University agrees it is important to establish consistency of interaction strength, while Jesse Thaler of the Massachusetts Institute of Technology also encourages other experimentalists to enter the fray. Indeed, he believes it is vital. “Only a confirmation from an independent experiment would give me significant confidence in the ATOMKI result,” he says.

One collaboration planning to test the anomalous result is DarkLight, based in the US. This will look for evidence of the 17 MeV/c2 boson by firing electrons from the Jefferson Lab’s CEBAF injector at a tantalum target. According to co-spokesperson Richard Milner of MIT, the experiment should produce results within the next couple of years – assuming that scientific approval and funding are forthcoming.

Contrast-enhanced MRI shines light on liver cancer survival

© AuntMinnieEurope.com
© AuntMinnieEurope.com

Researchers from France have shown that hepatobiliary MR contrast agent uptake can predict survival in patients with resectable hepatocellular carcinoma (HCC) as well as 18F-FDG PET/CT can. They published their findings in European Radiology.

Sébastien Mulé, a radiologist from Henri Mondor University Hospital in Créteil, south-east of Paris, and colleagues found that in 32 patients with 35 surgically proven HCCs, the quantitative analysis of the hepatobiliary phase (HBP) tumour enhancement in gadobenate dimeglumine (Gd-BOPTA)-enhanced MRI (lesion-to-liver contrast enhancement ratio, LLCER) accurately identifies moderately to poorly differentiated and/or microvascular invasion (MVI)-positive HCCs.

Compared with dual-tracer 18F-FDG and 18F-fluorocholine PET/CT, the contrast-enhanced MRI method performed well for the prediction of tumour aggressiveness and recurrence-free survival (RFS). Gd-BOPTA-enhanced MRI with delayed HBP images deserves consideration as part of pre-surgery workup in patients with resectable HCC, the authors noted.

MR and dual-tracer PET/CT
MR and dual-tracer PET/CT imaging in a 41-year-old man with poorly differentiated 90-mm HCC lesion in the right liver lobe. (Courtesy: European Radiology)

“The findings confirm our impressions in clinical routine. Indeed, we noted that HCC without significant enhancement at the hepatobiliary phase had higher histological grades than the other ones. Therefore, we were not surprised that the HBP tumour enhancement may also help predict recurrence-free survival,” Mulé told AuntMinnieEurope.com in an email.

However, he added that the strength of that predictive ability surprised the team in part, particularly because 18F-FDG PET/CT is of such well-established prognostic value in patients with HCC.

“PET/CT using 18F-FDG allows the identification of poorly differentiated HCCs at the expense of a relatively lower sensitivity for the detection of well-differentiated HCCs. 18F-FDG has also been shown to negatively correlate with tumour differentiation,” the authors wrote, emphasizing that 18F-FDG positivity may help predict both MVI and early recurrence after surgical resection, while PET/CT with radiolabelled choline – i.e., 11C-acetate or 18F-fluorocholine (18F-FCH) – is of great interest to detect well-differentiated HCCs.

Study details

All patients with untreated HCC who underwent 18F-FDG PET/CT as part of workup before liver resection or orthotopic liver transplantation at Henri Mondor University Hospital between October 2013 and January 2018 were considered eligible for the study (n = 71), and patients were included if they also underwent preoperative liver MRI with HBP imaging. A total of 36 people met the inclusion criteria.

All patients underwent Gd-BOPTA-enhanced MRI including delayed HBP images, 18F-FDG PET/CT, and (for 29/32 patients) 18F-FCH PET/CT during the two months prior to surgery. For each lesion, the authors calculated the LLCER on MRI HBP images and the SUVmax tumour-to-liver ratio (SUVT/L) for both tracers. They analysed and compared the predictive value for aggressive pathological features, including the histological grade and MVI, as well as the RFS.

The areas under receiver operating characteristics for the identification of aggressive HCCs on pathology with LLCER, 18F-FDG SUVT/L and 18F-FCH SUVT/L were 0.92 (95% confidence interval [CI] 0.78, 0.98), 0.89 (95% CI 0.74, 0.97; p = 0.70), and 0.64 (95% CI 0.45, 0.80; p = 0.035).

LLCER was identified as an independent predictor of RFS (HR [95% CI] = 0.91 [0.84, 0.99], p = 0.022). LLCER of -4.72% or less also accurately predicted moderate to poor differentiation grade (sensitivity = 100%, specificity = 92.9%) and MVI (sensitivity = 93.3%, specificity = 60%) and identified patients with poor RFS after surgical resection (p = 0.030).

After surgical resection for HCC, patients with an LLCER of -4.72% or less had significantly poorer recurrence-free survival than patients with an LLCER superior to -4.72%, according to the authors.

“HBP tumour enhancement after Gd-BOPTA injection may help identify aggressive HCC pathological features, and patients with reduced recurrence-free survival after surgical resection,” they wrote.

Impact of research

Based on the study findings, senior author and radiologist Alain Luciani and the rest of the team have changed their routine practice by integrating Gd-BOPTA-enhanced MRI with delayed HBP images as part of pre-surgery workup in all patients with resectable HCC.

Sébastien Mulé
Sébastien Mulé.

“PET/MRI with 18F-FDG is now performed in our institution as part of HCC pre-treatment workup,” Mulé noted. “Improving lesion characterization and prognostic prediction by systematically performing acquisitions at the hepatobiliary phase may be an interesting next step. Further studies will evaluate whether hepatobiliary MR contrast agent uptake may help optimize therapeutic management strategy in patients with HCC.”

Staff at the Henri Mondor University Hospital have been and still are involved in the care of COVID-19 patients, and the pandemic has had a significant impact on the organization and the clinical activity of the radiology department, he said.

“Notably, the management of patients with HCC was significantly altered, as patients were more likely to wait before they consult, and thus to present with more advanced stages of disease,” Mulé added.

  • This article was originally published on AuntMinnieEurope.com ©2020 by AuntMinnieEurope.com. Any copying, republication or redistribution of AuntMinnieEurope.com content is expressly prohibited without the prior written consent of AuntMinnieEurope.com.

Reality check: COVID-19 and UV disinfection

Video transcript

00:00–00:08
It’s fair to say there has been confusion about how ultraviolet light can help in the COVID-19 pandemic.

00:09–00:17
Sadly, it’s obscured some of the genuine science, which could actually be very significant. So let’s try to clear up some of the misinformation.

00:19–00:30
Now, when it comes to UV light, we are most familiar with UVA and UVB – the bands of sunlight that filter through the atmosphere and make it to the Earth’s surface.

00:31–00:35
In moderate doses it’s good for us in a number of ways.

00:36–00:44
But overexposure can cause sunburn – or even cancer – so that’s why we slap on the suncream, or shelter under parasols.

00:45–01:00
Fortunately, the ozone layer filters out an even more dangerous band of sunlight known as UVC. If you exposed yourself to UVC, you would experience serious burns and damage to DNA.

01:01–01:12
But UVC is a double-edged sword. As well as damaging skin, it can also mangle the genetic material of viruses and bacteria, preventing them from reproducing.

01:13–01:27
Scientists have known for over a century about UV’s ability to disinfect. And for many years, UVC lamps have been used for sterilization in medical settings, food production and a number of other places.

01:28–01:37
During the COVID-19 outbreak in China, buses were even bathed in UV light overnight, to leave them clinically clean for the next day.

01:38–01:53
For these applications, UVC lamps are great. But they’re often big and unwieldy. And because of the high risk to humans, operators need to wear really hardcore safety equipment and go through specialized training.

01:53–02:02
But now, emerging research could prove to be a game-changer for UVC sterilization. Making it much more accessible.

02:03–02:16
Researchers have discovered that a specific wavelength of UVC light – 222 nm – could be much less dangerous to humans, while still lethal for viruses and bacteria.

02:17–02:21
Now think about that for a second. The implication is huge.

02:22–02:32
In theory, we could deploy 222 nm lights across the world to shield ourselves from coronaviruses, and a bunch of other invisible enemies.

02:34–02:49

But before you get too excited, there is a long way to go and many questions still remain. Crucially, this far-UVC light has so far only been tested on mice at short exposure times and single doses.

02:50–03:01
So clearly, much more research is needed to check its safety for humans, and its ability to damage SARS-CoV-2, the virus behind COVID-19 disease.

03:02–03:11
And even if it does work, we would still to develop new lighting technologies, that are practical for a variety of applications.

03:11–03:24
The most promising approach seems to be light-emitting diodes – LEDs. And several groups of physicists are already experimenting with different materials to develop far-UVC LEDs.

03:25–03:36
Even the most optimistic researchers would admit that it is unlikely the technology could be ready in time for the COVID-19 pandemic, even if there is a second wave.

03:36–03:51
But the number of zoonotic diseases – that’s diseases passing from animals to humans – has been on the increase in recent times. So these far-UVC LEDs could come to play a vital role in the next serious pandemic.

03:52–03:59
Find out more about UV light and sterilization in the June 2020 issue of Physics World.

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