Dose distributions for brain tumour treatments with intensity-modulated proton therapy and proton arc therapy. (Courtesy: Yunzhou Xia)
The techniques used to deliver photon-based radiotherapy have advanced over the years, from 3D conformal radiotherapy, to intensity-modulated radiotherapy (IMRT) and volumetric-modulated arc therapy (VMAT). Each progression aims to confer higher conformality, faster delivery and increased plan robustness. Proton therapy technology has also evolved, from passive scattering to scanned pencil beams and intensity-modulated proton therapy (IMPT). But what’s next?
According to Yunzhou Xia from the University of Manchester, the next evolution in proton delivery is proton arc therapy (PAT). “Arc therapy is treatment with the radiation continuously on as the gantry rotates around the patient,” she explained. “It is different to IMPT, where the beam is switched off between gantry movements.” Unlike VMAT, however, PAT has only been studied since 2016 and is not yet part of routine clinical practise.
Speaking at the recent Medical Physics & Engineering Conference (MPEC), Xia described how the Bragg peak could make proton treatments sensitive to range uncertainties and set-up errors, and suggested that the greater number of control points in PAT compared with IMPT might increase the robustness of PAT treatment plans to uncertainties.
To assess the potential benefits of this approach, Xia created IMPT and PAT plans for one brain cancer and two head-and-neck cancer cases, with equivalent prescriptions for each pair of plans. She simulated range errors in the plans, including +/-3% over/undershoot and set-up errors of up to 3 mm in all directions. She then evaluated the dose distribution of each plan.
Xia first showed the audience the dose distributions for the brain tumour case, an ependymoma, for error-free IMPT and PAT plans. “In terms of target coverage, the two plans are very similar,” she said. “In the medium dose region, PAT delivers a more conformal dose to the target. However, in the lower dose region, PAT has more coverage.”
She then presented the values of conformity index (CI) and homogeneity index (HI) – tools used to quantitatively assess treatment plan quality – for pairs of plans with various uncertainties. PAT resulted in improved CI and HI values (closer to 1), for both range and set-up errors. This finding demonstrates that, for the ependymoma case, the PAT plans were more robust to errors than respective IMPT plans.
For the unilateral head-and-neck case, Xia showed that with no errors present, the PAT plan exhibited higher conformality and spared parts of the parotid gland compared with the IMPT plan. For plans with range errors, the CI and HI values were better with PAT than for IMPT, but PAT performed less well in plans with set-up errors.
Finally, Xia showed a bilateral head-and-neck case, with two target volumes: the first with a higher dose prescription than the second. Again, in the error-free instance, the PAT plan showed higher conformality than the IMPT version.
For the second, lower-dose, head-and-neck target, HI and CI values were closer to 1 for PAT plans than for IMPT, under both range and set-up errors. For the higher-dose target, CI was improved in the PAT plan while HI was better in the IMPT plan.
“Proton arc therapy has the potential to improve target robustness for certain brain and head-and-neck cases,” Xia concluded. “The narrower distribution of metrics in some cases may be beneficial for robust optimization.” Xia now plans to repeat this analysis using more cases in order to draw a statistical conclusion.
Part art book, part popular science, Space Dogs: the Story of the Celebrated Canine Cosmonauts evolved from a private collection of objects, which turned into a photography project. Not so surprising, considering that the collector and artist in question is Martin Parr, a celebrated photographer based in Bristol, UK. But why did he spend 20 years collecting memorabilia related to the Russian space dogs of the 1950s and 1960s?
Aside from the quirkiness factor, the objects form a record of a less-well-known story from the history of space travel, which is here told by science journalist Richard Hollingham, alongside Parr’s photos of his memorabilia collection and original press photos of the doggy heroes and heroines (mostly the latter).
From the dozens of dogs used in secret early experiments in low-pressure chambers and in suborbital flights, to the media furore surrounding the Soviet Union’s famed mongrel Laika and her successors, Hollingham packs plenty of fascinating detail into a small space. He explains why there were so many stray dogs on the streets of Moscow and the criteria for which strays were selected by Soviet scientists – including the requirement that they be light-coloured to show up well on TV cameras.
Hollingham doesn’t shy from including the sad deaths of some dogs, or the suffering that many survivors endured, though he also includes details of how well-loved they were by their team of scientists, doctors and engineers. The book devotes most of its pages to Laika, Belka and Strelka – the most famous and celebrated space dogs – but does find room for other canine characters. For example, the book talks about Ugolek and Veterok, the dogs whose mission lasted for 22 days in 1966 (they held the record for the longest spaceflight of any creature until 1971); and Tsygan and Dezik, the first dogs to experience suborbital flight, in 1951.
Parr’s photographs are equally revealing. In a Soviet Russia where individualism was deterred and celebrity shunned, the state not only deliberately turned its animal cosmonauts into superstars, but it did so through an array of commercial products. There are clocks, stamps, plates, books, confectionary boxes, pen holders and much more. And did you know there was a Russian-made “Laika” brand of cigarettes that lasted until 1990?
This small book is stylishly designed, striking a balance between humour, pathos, historical facts and adorable photos of dogs. What more could you want?
A high-voltage transmission electron microscope (HVTEM) small enough to fit inside a university lab has been built for the first time by researchers in Japan. The team, led by Takumi Sannomiya at Tokyo Institute of Technology, used radio-frequency (RF) cavities to chop and accelerate electrons into coherent beams. Their achievement comes five decades after researchers first attempted to use RF linear accelerators for electron microscopy – and could lead to a wide range of new sub-nanometre imaging applications.
TEM uses the wave-like properties of electrons to obtain images of thin samples (100 nm or thinner) with spatial resolutions better than 1 nm. TEM has allowed scientists to visualize objects as tiny as single hydrogen atoms.
Most TEMs use beams of electrons in the energy range 60-300 kV but higher energy electrons offer two advantages. First, higher-energy electrons have shorter wavelengths and therefore will reveal smaller features. Second, higher-energy electrons can pass through thicker and denser samples, increasing the types of samples that can be imaged.
Much too large
One barrier to boosting the energy of TEMs is the size of conventional electrostatic electron accelerators. A room-sized implementation is limited to about 300 kV, whereas a HVTEM running at 1 MV must be housed within a building-sized space.
Since the 1970s HVTEM designers have tried to overcome this problem by using RF cavity accelerators, which in principle can deliver high-energy electrons in a much smaller space. However, the lack of coherence of the electron beams from such accelerators has made this difficult.
Synchronized chop
Sannomiya’s team have solved this problem by using a series of RF-cavity components that maintain the coherence of the beam. The beam is created at 100 kV using a standard TEM accelerator. It then passes through the two RF-cavity choppers where it is cut into pulses that are synchronized for the next stage of the journey, which is a 400 kV RF-cavity accelerator. This synchronization ensures that coherent pulses pass through the sample. The transmitted electrons are then decelerated to 200 kV using a final RF cavity accelerator so that they can be focused and detected using a standard TEM set-up.
The team’s instrument is small enough to fit comfortably in their lab, but can still accelerate electrons to 500 kV, which is around half the energy acheiveable at much larger facilities. Sannomiya and colleagues demonstrated the efficacy of their HVTEM by imaging sub-nanometre features within micron-thick samples – much thicker than the 100 nm limit of most TEMs.
The team now hopes to improve their microscope further using superconducting cavities, which would accelerate electron beams to even higher voltages, while making the device more compact and energy efficient. With these upgrades, the HVTEM could find a diverse range of new imaging applications, including atomic-scale tomography for biological tissues and whole cells, as well as in situ observations of liquid and gas environments.
Traditional paddy fields are flooded with a shallow layer of water for around 80% of the growing season. In response to rising demand for water, rice farmers have experimented with less water-thirsty methods in recent decades, including alternate wetting and drying, and mid-season drainage of the field. Short-term studies indicate that these methods can maintain yields. But whilst the new techniques save water, they may reduce soil fertility in the long run, according to a recent study.
John Livsey from Stockholm University in Sweden and colleagues conducted a meta-analysis to assess the effect of common water-saving techniques for rice agriculture on soil organic carbon and greenhouse gas emissions. They identified twelve studies that contained relevant data on soil carbon balance in both flooded and water-saving conditions. Analysing this data revealed that water-saving irrigation practices reduced methane emissions by over 50% and carbon-dioxide equivalent emissions by 18%.
At the same time the alternative irrigation techniques reduced soil organic carbon by 5% compared to traditional irrigation. That’s because soil moisture plays an important role in regulating soil organic carbon.
“In flooded conditions oxygen within the soil quickly becomes depleted and respiration switches from aerobic to anaerobic,” says Livsey, whose findings are published in Environmental Research Letters (ERL). “This results in a much slower breakdown of organic matter and accumulation of soil organic carbon.” Under drier conditions the faster breakdown of organic matter releases other nutrients, including nitrogen, that were chemically bound to the organic matter.
In the short term, the changes in soil organic carbon are negligible but over the longer term they may degrade soil fertility, potentially reducing yields and limiting future yield increases. Rice is a staple food for around half the world’s population.
Livsey and his colleagues suggest that water-saving practices receive tweaks to minimize their impact on soil fertility. “These could include restricting the extent to which soils are allowed to dry, or the number of times that fields are dried and re-flooded within a growing season,” he says.
What’s more it may be possible to mitigate impacts by leaving plant residues on the field after harvest or adding organic matter such as manure. For now though, the priority has to be more long-term data to understand the effects of water-saving practices better, with initiatives like the Sustainable Rice Platform playing a vital role.
The integrity of US government research is under siege and has been significantly weakened during the current administration of Donald Trump. That is according to a report by National Task Force on the Rule of Law and Democracy, which notes that recent presidential administrations have not only manipulated the findings of government scientists and researchers but also “retaliated against career researchers for political reasons”. It calls for Congressional legislation to protect the independence of government science data.
The report states that — along with manipulating findings and retaliations against scientists — US governments have also invited “outside special interests” to shape research priorities; “undermined and sidelined” advisory committees staffed by scientists; as well as suppressed research and analysis from public view – often material that had previously been made available. In many cases, the report adds, the administrations “have appeared to pay little political price for these missteps”.
We are at a crisis point, with almost weekly violations of previously respected safeguards
The task force, based at New York University’s Brennan Center for Justice, lists a number of issues that occurred under the two presidents who preceded Donald Trump. In the George W. Bush administration, for example, a politically appointed public-affairs officer prevented NASA climate scientist James Hansen from talking to the media in order, he said, to make the president look good. And political officials in the Obama administration’s Environmental Protection Agency (EPA) tried to downplay the risks to drinking water in a report on fracking, although scientists managed to reverse the decision.
‘Weekly violations’
Although previous presidents injected some politics into science, the report states that the Trump administration has tried both to politicize scientific and technical research on a range of topics and to undermine the value of objective facts themselves. “Now, we are at a crisis point,” the report declares, “with almost weekly violations of previously respected safeguards”.
Recent events, for example, include the “Sharpiegate” affair, in which the National Oceanic and Atmospheric Administration excoriated its weather forecasters for disagreeing with President Trump’s incorrect assertions about the path of Hurricane Dorian. The EPA also prevented academic researchers from serving on its scientific advisory boards in favour of industry-connected individuals. Another issue cited is the relocation of economists at the agriculture department from Washington after they revealed the harmful impact of the administration’s trade policies on farmers.
Writing in the Washington Post, panel members Christine Todd Whitman, who served as EPA administrator during George W Bush’s presidency, and former US attorney Preet Bharara note that Trump’s presidency “has exposed serious fissures in our system of government that require repair – especially when it comes to the integrity of government research”.
Infiltration of immune cells into melanoma. The images show tumour cells in blue and immune cells (CD8, CD4, natural killer and macrophages) in red, for control mice at day 5 (top row), mice treated with MRT at day 9 (middle row) and mice treated with conventional radiotherapy at day 9 (bottom row). (Courtesy: Int. J. Radiat. Oncol. Biol. Phys. 10.1016/j.ijrobp.2019.08.027)
Microbeam radiation therapy (MRT) uses synchrotron X-ray beams to deliver spatially fractionated radiation, with extremely high peak doses deposited in the microbeam path and tissue located between the microbeams receiving only a small fraction of this dose. MRT has proved highly effective in treating various tumours in small animals, while selectively sparing normal tissues. However, the mechanisms underlying the therapeutic efficiency of MRT are not well understood.
Malignant melanoma is one of the most aggressive cancers and is often radioresistant. “Although the main treatment for melanoma is surgery, in some cases resection is impossible due to the location of the tumour,” explains first author Marine Potez. “We wanted to find an alternative treatment for these tumours.”
With this aim, Potez and colleagues implanted radioresistant melanoma cells into the ears of mice. Roughly 10 days later, they divided the mice into three groups: 47 to be treated with MRT; 28 treated with conventional broad beam irradiation; and 26 non-irradiated controls. They performed all experiments using synchrotron X-rays produced at the European Synchrotron Radiation Facility.
The researchers treated the conventional group using a homogeneous 7.5×15 mm beam to deliver 6.2 Gy to the tumour. For the MRT treatments, the 7.5×15 mm irradiation field was covered by 37 quasi-parallel, 50-μm wide microbeams, with a peak dose of 407.6 Gy and a valley dose of 6.2 Gy.
Measuring tumour size before irradiation, on the day of treatment and then daily showed that both types of radiotherapy impeded melanoma growth compared with controls. Tumour volume doubled in 2.1 days in the control group, 3.7 days in the conventional group and 6 days in the MRT group. MRT significantly attenuated growth, with tumours shrinking from days 4 to 8 and then slowly growing again. Conventional irradiation, however, could not stop progression even temporarily, with tumours in this group exhibiting almost exponential growth throughout the study.
Irradiation set-up showing radiochromic film placed behind the irradiated ear. (Courtesy: Marine Potez)
Underlying mechanisms
To investigate why MRT offers better tumour control than conventional radiotherapy, the researchers first examined the impact of radiation on tumour blood vessels. They found that MRT altered blood vessel integrity and significantly reduced blood perfusion into irradiated tumours. At day 5 after irradiation, for example, 68.5% of vessels in the MRT group were perfused, compared with 86.3% and 81.5% for conventional and control groups, respectively.
Irradiated tumours also exhibited a reduced tumour cell proliferation index compared with controls, from day 2 in the MRT group and day 5 in the conventional group. MRT resulted in lower proliferation rates, with maximum divergence on day 9 when the proliferation indices were 14.5% and 70.9%, for MRT and conventionally treated tumours, respectively.
Immunostaining excised tumour slices for senescence – in which cells no longer divide but are still metabolically active – revealed a marked increase in senescence after MRT from days 2 to 9, compared with the other groups of mice.
This MRT-induced senescence significantly enhances the production of chemokines involved in recruitment of monocytes (a white blood cell involved in immune processes) in tumour tissue, which the team confirmed using Bio-Plex immunoassays. This led to a massive influx of immune cells (macrophages, natural killer cells, CD4+ and CD8+ T lymphocytes) in MRT-treated tumours from day 5 to day 12, which can induce inflammatory and anti-tumour immune responses.
“We observed that the first tumour response after MRT was vascular damages and senescence,” says Potez. “We hypothesized that the high influx of immune cells, recruited by the senescence-associated secretory factors, caused the vasculature impairments.”
The researchers suggest that MRT represents a promising candidate for new clinical trials to explore the clinical relevance of these anti-tumour effects. Currently, however, MRT is in the pre-clinical stage, including trials on pets with spontaneous tumours and on pigs, which provide a good intermediary between small lab animals and human patients.
Potez notes that due to the particular irradiation geometry of MRT, positioning and treatment planning are still under development for patients. “Also, MRT can only be performed at third-generation synchrotrons to fulfil the requested parameters, such as the dose rate and parallel-non divergent microbeams,” she says. “To be more accessible for patients, the development of compact sources is ongoing.”
In the next stage of this project, the researchers are characterizing the infiltrating immune cells. “We are also testing different treatment protocols with multiple irradiations and ports, and we are combining MRT with nanoparticle injection,” Potez tells Physics World.
Gaining a degree in physics is no mean feat. As a student, you’re busy completing lots of assignments in many different modules, and tackling experiments in the lab too. So it isn’t surprising that, for most students, extracurricular activities often fall into a black hole of “things you don’t have time for”. However, having a rich life outside your core academic activities is vital when it comes to helping you figure out what you want to do after you graduate, and getting the right job.
While good grades are important, students also need a broad range of transferable skills. This includes learning prioritization, communication, teamwork and problem solving; taking initiative, showing resilience and leadership; and developing business acumen and skills such as negotiation and persuasion. The need for transferable skills isn’t limited to jobs in industry – you’ll need these skills even if you want to build an academic career.
Indeed, in my experience of working with companies that hire physicists, the most employable graduates are those who engage in extracurricular activities. By doing so, students are exposed to new and challenging environments, which builds their confidence, and often leads to further opportunities.
Such extracurricular activities includes not only part-time jobs, summer placements and internships, but also everything from coaching, tutoring and managing your physics society to sitting on a committee, contributing to a special interest group, organizing events or volunteering. By participating in these activities, you are, consciously or unconsciously, preparing yourself for the next stage in your life, wherever this takes you.
Taking up a placement or internship, especially in a field or company that you may want to work for, is a particularly good idea. There are many ways to go about this. While you can find a placement or internship under your own steam, there are many resources in place to help. For a start, speak to your careers adviser or tutor, who can point you in the right direction. The Institute of Physics (IOP) also offers a number of opportunities to help you gain experience and develop those all-important transferable skills (see box below). A handful of graduate training programmes have even been officially accredited by the IOP, all of which combine dedicated events, training modules, professional development, mentoring and on-the-job experience.
The IOP currently works with 21 companies, from Atkins and Leonardo to EDF and Sellafield, which deliver graduate training programmes for physics students, through the Accreditation of Company Training Schemes (ACTS). Accreditation indicates that the training scheme has the appropriate criteria for physicists working towards gaining professional registered status.
The message is clear – transferable skills are essential. But instead of trying to convince you any further myself, here are some case studies of physics graduates who have taken up a host of placement and volunteering activities.
Molly Burkmar.
Molly Burkmar
I’m currently studying for an MPhys in physics, astrophysics and cosmology at the University of Portsmouth, UK.
During my second year I decided to apply for South East Physics Network (SEPnet) placements, after learning about the organization at a careers day at university. SEPnet links university physics departments in south-east England and organizes summer placements for physics undergraduates and PhD students to develop their employability skills and raise awareness of their career options in business and industry. I looked through the profiles of more than 60 placements and applied for five, but it was the placement at Winchester Science Centre that caught my eye, as I’m thinking about going into teaching. Thankfully, the interview went really well and I was offered the job. I was really nervous to start with as this was my first job in the science industry, but the team was very welcoming, and I got settled in quickly.
My placement at Winchester was split into two parts: being an “inspirer” and evaluating an exhibit. Most of my time was spent on the former, which involved science busking, floor walking around the exhibits and presenting the live science show. My project involved evaluating a display known as “Stem Cell Mountain” and recommending how to improve it.
My confidence has increased from presenting shows. I was nervous about doing them to begin with, but I started by teaming up with another member of staff to deliver them and presented my first solo show in front of the head of the planetarium. This was really helpful to gain confidence and get constructive feedback before doing them solo and it became my favourite part of the job. I have gained so much experience being an educator too. I picked up tips on how others presented and taught around the centre, which helped me to successfully communicate to a wide range of ages and science backgrounds. Seeing children learning and getting excited about science has been the most rewarding part of the job.
I used skills from my laboratory module at university during the project, such as keeping a lab notebook, but I’ve also learnt a lot about evaluation. I’ve taken observations, semi-structured interviews and surveys as well as analysed both quantitative and qualitative data. I then used the data to make small modifications to the exhibit to see if they were successful so I could make recommendations on how to improve it. My study was one section of a bigger project to modify Stem Cell Mountain, but it was really interesting to see the evaluation side from start to finish.
By undertaking a placement, I’ve gained so much experience that I can use to help me with the rest of my degree and when applying for jobs. I would really recommend completing a placement in an area you’re interested in as there are a lot of job-specific skills that can’t be taught at university.
Adam Powell.
Adam Powell
I am a graduate student with the University of Calgary, Canada, as a member of the Antihydrogen Laser Physics Apparatus (ALPHA) collaboration at CERN.
During the foundation year of my physics degree at Swansea University, UK, when the opportunity to lead the university’s physics society arose, I leapt at the chance. I had begun my degree at a disadvantage, not having taken maths past the age of 16, so I was all the more motivated to find my place. A few months after taking on the society, I had helped to organize the first in a number of careers events to help my peers (and myself) see the vast number of possible pathways through physics. This was also my first interaction with IOP Wales, and my first outreach event came soon after – eventually I became a campus ambassador and nations committee member.
As my network started to grow, I was offered an internship with the university’s employability academy. I spent a summer focusing on the softer skills that are incredibly important in an increasingly competitive workplace. I was encouraged to apply for the Undergraduate of the Year awards sponsored by Target Job and was shortlisted in the men’s category. The reward for this was an interview at L’Orèal UKI. I was aware of the brand but had no experience in the beauty industry. Determined to show what I could do for them, I took the sample data provided and set to work on analysis. After combining skills learnt through my studies with some impromptu market research (questioning the unfortunate travellers on a Swansea to London train about the various products) I was offered a summer placement in the business development team. While my time with L’Orèal was full of very valuable learning experiences and wonderful people, it wasn’t for me long-term. I learnt the most valuable lesson of all – that it is just as useful to know what you don’t want to do, as what you actually want to do.
I returned for my final year at Swansea, now as an MPhys student, with a desire to focus on research. I was then incredibly fortunate to be sent to CERN to carry out my final-year project with the ALPHA experiment. I spent three months working in an environment that pushed me every day, and I was hooked. Knowing that I wanted to return after my MPhys, I set about trying to find a postgraduate position. A few discussions later, I was hired as a research assistant by the TRIUMF laboratory in Vancouver to help in the construction of the new ALPHA-g experiment at CERN. This then led to my current place as a graduate student with the University of Calgary as a member of the ALPHA collaboration and I currently hold a Leverhulme Trust Study Abroad Studentship.
Despite now being based outside Wales, I’m still a regular volunteer and committee member, and played a role in organizing the IOP-sponsored Conference of Astronomy and Physics Students 2019 at Swansea.
After the first year of my Master’s degree, I was looking for opportunities to gain some experience working in professional labs, which I saw as necessary for my career plan. I found many of the adverts on GRADnet interesting, but was particularly keen on working at the National Physical Laboratory, because most companies advertised for data science internships, whereas NPL’s placement was focused on experimental physics.
I worked on a project to build a method to reconstruct the spectrum of a 2D material using photoluminescence imaging techniques. This involved using the LabView platform, which is an indispensable tool in experimental physics. I also worked in an optics lab where I learnt not only how to work with several instruments, but also how to approach a new and unfamiliar instrument. While it was a struggle to transfer my bookish knowledge to real-life experiments, I learnt what experimental physics actually entails.
The placement helped me sharpen both my technical and professional skills. The standard of professionalism expected of a student is not that expected in a real working environment and I learnt a lot by just watching my superiors and peers every day. Indeed, I believe this placement was one of the most important learning experiences of my career so far, and will help me work on future projects more efficiently.
I also made many friends who were mostly PhD students. From them, I was able to get a great insight into how the organization worked and all its activities. They were then able to give me advice about what they would have done differently before starting their PhD.
The placement was an invaluable learning experience. I would highly recommend anyone who has the chance to take up a summer placement with SEPnet, GRADnet or the IOP, and to utilize it to its fullest.
During the second year of my MPhys degree in physics at the University of Surrey, UK, I began to think more seriously about what I wanted to do after I graduated. Pursuing a career in research had always interested me, so I figured that a research-orientated placement would be the perfect opportunity to discover first-hand what it is like to work in a research environment. This led to me applying for an eight-week SEPnet summer placement at the National Physical Laboratory in Teddington. There, my role was to evaluate a phenomenon known as “non-uniqueness”, associated with standard platinum resistance thermometers used to realize the International Temperature Scale of 1990.
Non-uniqueness is a very subtle form of uncertainty associated with temperature measurement that, as a result of the ever-improving precision to which we can perform temperature measurements today, is becoming a fundamental limiting factor in the accuracy we are able to achieve. My task during the placement was to try to quantify the uncertainty associated with this non-uniqueness in the thermometers. The first half of the placement was spent performing measurements in the lab, where I determined the resistance ratios of the thermometers in temperature-controlled oil baths, liquid nitrogen and fixed-point cells, over a range from –196 °C to 232 °C. I then plotted and analysed the data collected in order to gain a clearer picture of how non-uniqueness affects our most accurate temperature measurements.
This was my first experience of not only collecting high-quality experimental data but also of performing careful data analysis, both of which are absolutely invaluable skills for a career in research. Conducting research during my placement was a very different experience to studying at university, as many of the questions we were asking didn’t have a known answer. This aspect of exploring the unknown is something I found really exciting and it led to me developing a wide range of useful skills, from critical thinking to problem solving.
Working at NPL definitely confirmed my desire to work in a research environment and showed me the wide variety of opportunities available. I was constantly asking the staff at NPL about their research and everyone was very happy to share their work with me, so I got to learn a lot about metrology/traceability of measurement and its importance in every aspect of our lives.
For any undergraduate interested in expanding their skill set and experiencing the real-world implications of what they are taught in lectures I would highly recommend carrying out a placement. Not only does it look great on your CV, it also provides some invaluable tools for a potential career in research in the future. Don’t be put off applying if you don’t have a lot of direct knowledge about the placement subject area, as plenty of help and support are provided. I knew nothing about the world of metrology before my placement, but I found the scheme to be a fantastic opportunity to extend my knowledge of a given area.
How the IOP can help you
The Institute of Physics (IOP) is here to support you in building a successful career through our programme of activities. Members of the IOP can:
Become a part of the IOP student community and participate in a host of activities to develop skills: iop.org/student-community
Volunteer for IOP-led physics engagement activities to practice your communication, organizational and teamwork skills: iop.org/volunteer
Plan and organize scientific meetings, working in collaboration with other IOP groups and sister societies. Promote events through your institutions and networks, and coordinate and generate digital content for your chosen group(s): iop.org/groups
Gain an advantage in the job market by attending our employer-led careers events and participate in career-themed webinars. You can also participate in events and conferences, at exclusive member discounted rates, to keep up to date and network with peers and experts in academia and industry: iop.org/events
Make use of the IOP careers hub, which will support you in writing your CV, practising for interviews, delivering presentations, and effective time management, among many other useful resources to support your future career choices: iop.org/member-services
Take advantage of our international travel grants to attend conferences, such as the Research Student Conference Fund, the C R Barber Trust and Early Career Researchers Fund: iop.org/grants
Following graduation, join the Member grade and use the designatory letters MInstP after your name, to demonstrate your commitment and professionalism: iop.org/member
A new refrigeration technology based on the twisting and untwisting of fibres has been demonstrated by a team led by Zunfeng Liu at Nankai University in China and Ray Baughman at the University of Texas at Dallas in the US. As the demand for refrigeration expands worldwide, their work could lead to the development of new cooling systems that do not employ gases that are harmful to the environment.
The cooling system relies on the fact that some materials undergo significant changes in entropy when deformed. As far back as 1805 – when the concepts of thermodynamics were first being developed – it was known that ordinary rubber heats up when stretched and cools down when relaxed. In principle, such mechanocaloric materials could be used in place of the gases that change entropy when compressed and expanded in commercial refrigeration systems. Replacing gas-based systems is an important environmental goal because gaseous refrigerants tend to degrade the ozone layer and are powerful greenhouse gases.
In their experiments, Liu and Baughman’s team studied the cooling effects of twist and stretch changes in twisted, coiled and supercoiled fibres of natural rubber, nickel-titanium and polyethylene fishing line. In each material, they observed a surface cooling as high as 16.4 °C, 20.8 °C, and 5.1 °C respectively, which they achieved through techniques including simultaneous releases of twisting and stretching, and unravelling bundles of multiple wires.
Supercoiled fibres
The team also made supercoiled fibres of natural rubber in which the twisting and coiling were done in opposite senses (clockwise and anticlockwise). Much to their surprise, they found that these structures cooled when stretched, rather than heated.
The team also looked at microscopic changes in the materials. An X-ray diffraction crystallography study of the polyethylene fishing line revealed changes in molecular structures associated with the transition from low to high entropy phases. The team identified this process as the cause of the effect, which they have dubbed “twistocaloric” cooling.
Liu, Baughman and their colleagues then built a simple device from a three-ply nickel-titanium wire cable, which cooled a stream of running water by as much as 7.7 °C as it unravelled. They propose that far higher levels of cooling could be reached through additional cycles of twisting and twist release within the cable — resulting in a highly efficient fridge.
The team faces many challenges in creating commercially-viable twist fridges, including the need find a material that is not degraded by being repeatedly twisted and untwisted. So far, they have only explored few commercially-available materials, but now plan to expand their research to seek-out materials that have optimized mechanical and twistocaloric properties. If realized on commercial scales, twist fridge technologies could provide climate-friendly solutions to meeting our rapidly expanding demand for cooling.
Each of the five mass extinctions over the last 500 million years that saw at least 75% of species disappear was accompanied by a surge in carbon entering the ocean. But carbon pulses are relatively common and usually benign; there were around 30 over that same time period. So what sets mass extinction events apart?
A study suggests that Earth’s oceans have a distinct threshold when it comes to the amount of carbon they can process. Mass extinction events occur when the threshold is passed. Anthropogenic carbon dioxide emissions are comparable to the carbon surges associated with previous mass extinction events, suggesting that we’re likely to be triggering a sixth mass extinction event right now.
Carbon is constantly cycled around our planet. Photosynthesis converts carbon dioxide to organic carbon; respiration converts organic carbon back to carbon dioxide. Sometimes carbon ends up in a long-term store, for example when small ocean creatures such as coccolithophores sink to the sea-floor and lock the carbon into sediments, but eventually the carbon returns to the loop as, in this case, geological processes uplift the rocks and weathering releases the carbon to the atmosphere.
Many external triggers can disrupt the carbon cycle including variations in orbital motions, release of methane hydrates, meteorite strikes, evolutionary changes and volcanic emissions. Ocean sediments record those disruptions, with carbon-rich rocks forming when atmospheric carbon dioxide levels are high. Until now, the consensus has been that the ocean responds proportionately to the amount of carbon being pumped into it: the larger the trigger, the more carbon-rich the ocean sediments become.
However, Daniel Rothman from Massachusetts Institute of Technology, US, was puzzled by the fact that, regardless of their size, most carbon pulses result in a characteristic rate of change in the ocean’s store of carbon but mass extinction events appear to have a far greater rate of change. To understand this anomaly, Rothman modelled the marine carbon cycle mathematically, exploring how disruptions to the incoming carbon flux were likely to influence the way that carbon was stored.
The model demonstrated that up to a certain limit, Earth’s oceans can absorb and process pulses of carbon dioxide and return to their steady state. But above a certain threshold, the oceans were pushed out of their steady state, resulting in acidification at the surface.
“I’m suggesting that the magnitude of the disruption is determined not by the strength of the external stressors but rather by the carbon cycle’s intrinsic dynamics,” says Rothman, whose findings are published in the Proceedings of the National Academy of Sciences (PNAS). His results suggest that this ocean threshold is yet another “tipping point”, beyond which there’s a nonlinear response.
By looking at the size and duration of the 31 disruptions to the global carbon cycle over the last 542 million years, Rothman showed that the majority have a characteristic rate of change, but that four of the five mass extinction events grew faster than this.
The model suggests that the ocean threshold also depends on the duration over which the carbon flux is increased. Relatively weak but long-lived perturbations, such as massive volcanic eruptions occurring over millions of years, can overshoot the threshold. But short sharp disruptions, like the intense pulse of carbon dioxide produced by current anthropogenic emissions, can pass the threshold too.
Rothman shows that today’s anthropogenic emissions and the carbon dioxide associated with massive volcanism in the past are roughly equivalent in their potential to pass the ocean threshold. This suggests that mankind’s actions may well trigger a mass extinction event. But because the oceans take a while to respond, it will be some time before the sixth mass extinction event becomes visible in the rock record.
“If the carbon cycle passes the threshold, the effects would play out over a period of ten thousand years or more,” says Rothman.
Map of tumour elasticity (in kPa) showing the marked stiffness of pancreatic tumours in a mouse model. (Courtesy: Yann Jamin/ICR)
Researchers from the Institute of Cancer Research (ICR) have used MR elastography to visualize and measure the stiffness and density of tumour tissues in mice. The non-invasive imaging technique provides crucial new information about cancer architecture and could help deliver treatment to challenging tumours (Cancer Research 10.1158/0008-5472.CAN-19-1595).
Tumours are formed from dense and compact networks of cells, structural fibres and blood vessels. Some tumour types are particularly stiff and dense, which makes it difficult to deliver drugs deep inside the tumour mass and hinders treatment. Tissue stiffening is also associated with tumour progression and metastasis. The major contributor to this increased stiffness is collagen – a key component of bone, cartilage, tendons and the extracellular matrix that holds tissues together.
Drugs designed to break down the extracellular matrix, such as collagenase, can weaken the structure that holds a tumour together and allow other cancer drugs to reach cells in its centre. Assessing the contribution of collagen to relative stiffness could identify tumours with the potential to be treated by with such drugs.
The ICR researchers, working in collaboration with King’s College London, combined MR elastography with computational histopathology to investigate the contribution of collagen to the biomechanics of several different tumour types in mice. They found, for example, that breast tumours were around twice as stiff as brain tumours and around three times as dense.
The pre-clinical study demonstrated that increased collagen correlated with elevated tumour elasticity and viscosity, with collagen key to keeping breast and pancreatic cancers stiff and inaccessible to treatments. In contrast, tumours arising from the nervous system, such as some forms of childhood cancer and brain tumours, were relatively soft and lacking in collagen.
“Our research shows that this new type of scan can give valuable diagnostic information about breast and pancreatic tumours non-invasively by assessing their stiffness,” explains study co-leader Simon Robinson. “If confirmed in a clinical trial, we could use this technique to identify patients most likely to benefit from treatments that target the dense scaffold upon which these tumours grow.”
The researchers also used MR elastography to monitor the weakening of tumour structure following treatment with collagenase. They found that collagenase resulted in a clear reduction in the elasticity and viscosity of breast tumours in mice – both of which fell by around a fifth. This finding suggests that the technique, which can be performed on a conventional clinical MRI scanner, could help identify the optimum time at which to deliver chemotherapeutic drugs by showing when the tumour is most vulnerable.
“There’s a lot of research activity centred on finding new therapies designed to help anti-cancer drugs reach their target in breast and pancreatic cancers, which can be so stiff and dense that they are impenetrable,” says study co-leader Yann Jamin. “We are very excited to have found a rapid scan that can be incorporated into a current routine clinical MRI examination and can potentially monitor the effects of these new tumour-weakening therapies, and assist the development and delivery of medicines which could save or extend lives.”
