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  1. US physics: a snapshot

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    From the percentage of overseas PhD students in the US to the proportion of physicists who work in the other university departments, Michael Banks takes a look at some of the numbers that characterize the US physics community

    The US has long been a powerhouse of physics, which shows no sign of abating anytime soon. The country has received more Nobel prizes than any other and, on a par with China, publishes the most papers. Helped by funding for physics that is the highest in the world – the National Science Foundation spends $7.5bn on science, while the Department of Energy’s Office of Science doles out $5.4bn on R&D – the US has world-class facilities with pioneering telescopes, leading neutrino centres and deep underground labs. One notable change in the country has been the rise in the number of students from abroad who do their PhD in the US. In 1970 there were only a couple of hundred PhD recipients who came from outside the US. That number is now close to 1000, almost on a par with the number of US-born PhD doctorate earners. Another development is the increase in the number of women in US physics. In 2002 just 7% of PhD students were women, but that proportion has now doubled. The percentage of female full professors has also doubled from 5% in 2002 to 10% in 2014. Yet diversity challenges remain. In 2015 more than three-quarters of physics faculty were white, higher than the general US population (64%), while only 2.5% of physics faculty in the US were black or African American, compared with around 13% of the overall population.

    • We would like to thank staff at the Statistical Research Center at the American Institute of Physics for providing the data shown here.

     

     

     

     

     

     

  2. Neutrons for industry

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    Pushing the limits. (iStock/mizoula)

    Several months ago, when my colleagues and I were debating which topics to highlight in the next few issues of Physics World’s focus series, there was one suggestion I wasn’t sure about: neutron science. It wasn’t the field’s intrinsic merit that made me hesitate. It was more a case of – well, I’m Physics World’s industry editor, and the focus series is supposed to be about applied and industrial physics, and, um, isn’t neutron science kind of…fundamental?

    Since then, I’ve learned that I was both right and wrong. Certainly, neutrons are a powerful tool for doing basic research, and scientists at neutron sources such as ISIS in the UK and the Institut Laue-Langevin in France spend a lot of time exploring fundamental material behaviour. What I didn’t appreciate is that industrial scientists and engineers are also taking a significant (and growing) interest in neutron-based measurements. As the case studies in this issue show, neutron data are making a difference in industries as varied as microelectronics, steel manufacturing and even dairy products. And that’s just the tip of the iceberg.

    Increased industry involvement does present some challenges for the neutron-science community. Data management is one area of concern. High-level efforts to make neutron data FAIR – findable, accessible, inter-operable and re-useable – offer significant benefits for researchers seeking to build on previous work. However, a blanket open-data requirement would send many industry users running for the hills, with fears over commercial confidentiality potentially outweighing the benefits of obtaining the data in the first place.

    Crafting data policies that promote openness while remaining sensitive to industry users’ needs seems an achievable goal. There is plenty of good will on both sides, and facilities are generally keen to engage with industry partners. But unclear and variable guidelines can be as off-putting as bad ones, and the current patchwork of facility-specific, case-by-case agreements on data confidentiality and industry access is not ideal. A more unified, community-wide approach would help attract new industry users and make multi-facility collaborations easier for existing ones.

    Finally, while preparing this issue I also realized that none of these neutron experiments – basic or applied – would be possible without what might be dubbed the “neutron industry”: the network of firms that help build new neutron sources and upgrade existing ones. Expanding this supplier base would benefit companies and facilities alike, but as with expanding industry access, a crucial first step is to make both parties aware of the other’s existence. I hope that in some small way, this issue will help accomplish that.

  3. flannel

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    The contents of this magazine, including the views expressed above, are the responsibility of the Editor. They do not represent the views or policies of the Institute of Physics, except where explicitly stated.

  4. Land of milk and neutrons

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    A Danish effort to bring neutron and X-ray scattering expertise to companies has reaped benefits for the dairy industry, and participants aren’t letting the grass grow under their feet. Erik Brok and Søren Roi Midtgaard outline plans to milk the partnership further

    Moo-tron science Neutron-based measurements reveal the structure of milk. (iStock/Gerard Koudenburg)

    If you go on a scenic drive through the Danish countryside, you will see a lot of cows. That is not surprising: Denmark has around half a million dairy cows, spread over less than 43,000 km2 of land. What is, perhaps, surprising is that there is a link between these placid, productive creatures and a multibillion-euro research infrastructure for neutron and X-ray scattering. The connection exists thanks to researchers at the University of Copenhagen, who spotted an opportunity to use advanced research facilities to investigate the complex hierarchical structure of milk and milk-derived products.

    The dairy studies date back to 2013, when the university, with support from the capital region of Denmark, began a pilot project to test the feasibility of employing X-ray and neutron scattering in industrial R&D settings. This project, known as NXUS (Neutron and X-ray User Support), established collaborations between industry and university scientists on many different topics, including the processes that take place when paint dries and techniques for enhancing the stability of protein-based drugs. However, dairy companies and their specific challenges were a major focus of the project, with companies such as Arla Food Ingredients, CO-RO A/S and DuPont Nutrition Biosciences ApS all interested in questions related to the processing and handling of milk products.

    Dairy details

    Milk is a complicated system with many constituent elements. However, some of its most important properties can be understood by considering it as a colloid of casein, or milk protein, arranged in globular agglomerates of thousands of individual casein molecules. These agglomerates are known as micelles, and their overall size is in the micron range. Closer examination, though, reveals that the substructure of these micelles is highly hierarchical, with features of various sizes. Examples include clusters of calcium phosphate that are only a few nanometres in size; groups of individual proteins that are some 15–20 nm across; and the overall structure of the micelle (hundreds of nanometres) and its surface. These substructures are very important for the properties of the milk, and in particular for the texture and “mouthfeel” of the finished product, whether it is yoghurt, cheese or anything else derived from milk.

    Small-angle neutron and X-ray scattering make it possible to study features with length scales from 1–1000 nm (see “Small-angle scattering” box), so they are perfect tools for studying casein micelles. One such study, performed in collaboration with DuPont Nutrition Biosciences, used a combination of SAXS and SANS to examine ways of stabilizing acidified milk in solution. Acidification of milk can lead to aggregation (or coagulation) of the casein micelles, and one needs to control this process in order to produce the desired dairy product – for example a certain type of cheese or yogurt – with the desired texture and stability. In this study, the structure of the casein micelles was studied before and after acidifying the milk, and before and after adding a stabilizing agent to the acidified milk. On a macroscopic level the samples differ in texture and the SAXS and SANS data reveal that at the nanoscale, too, there are clearly identifiable differences (see “Milking the data” figure). The data also illustrates the benefit of using both X-rays and neutrons, since some features are only visible in one of the two corresponding data sets.

    [[SUBARTICLE]]

    Armed with some prior knowledge of the constituents of casein micelles, it is fairly easy to deduce, from visual inspection of the data, what is going on. The disappearance, after treatment, of the feature visible around a scattering vector q = 0.08 Å–1 in the scattering curves of the untreated milk samples indicates that calcium phosphate clusters in the micelles disappear upon acidification. Furthermore, the general suppression of features in the middle range of the data, around q = 0.01 Å–1, indicates a collapse of the micelle’s internal structure. Finally, acidification seems to make micelles cluster together in larger aggregates, but this clustering is reduced when the stabilizer is added. This can be deduced from the increase in scattering in the very low-q range of the data (the far left in the figure) on acidification, followed by a slight decrease and flattening when the stabilizer is added. A more detailed analysis of these data enabled DuPont Nutrition Biosciences to better understand the effects of their natural stabilizers on micelle mechanics at a molecular level. Projects involving Arla Food Ingredients and CO-RO A/S similarly provided the companies with specific knowledge that they would not otherwise have gained.

    Assessing impact

     

    Milking the data Small-angle scattering data from representative measurements, clearly showing the structural difference between raw milk, acidified milk and acidified milk with an added natural stabilizer. These differences occur at various length scales and correspond to changes in the sub-structures of casein micelles in milk. SAXS data comes from the ID-02 beamline at the European Synchrotron Radiation Facility (ESRF) in Grenoble, France and SANS data from the KWS-2 instrument at the Forschungsreaktor München-II in Germany.

    With Denmark’s national milk production nearing 5 billion kg per year, and dairy exports worth €1.8bn to the economy annually, even a slight industry edge could have a large impact – not only for the individual dairy companies, but also for the country as a whole. But the effect is not necessarily limited to Denmark’s current industries. Richard B Larsen, a senior advisor at the Confederation of Danish Industry (CDI), argues that with the European Spallation Source (ESS) being built less than an hour’s drive from Copenhagen, and the neighbouring MAX-IV synchrotron facility already operating, international companies may choose to base their R&D departments in Denmark “due to the easy access and accompanying knowhow in applying neutrons and X-rays to investigate problems of industrial relevance.” With time, he adds, the expectation is that a robust industry research sector will generate highly specialized jobs that will, in turn, help realize the full potential of the area’s world-class research infrastructure.

    Larsen’s enthusiasm is mirrored by Lise Arleth, a professor at the Niels Bohr Institute at the University of Copenhagen and founder of the NXUS project. The institute has a long tradition of exploiting neutrons and X-rays for basic science, she explains, so “having the NXUS project embedded in my research group has been a great opportunity to get experience in actually performing these industrial R&D projects on a larger scale.” Getting a new generation of scientists involved in industrial challenges has also been rewarding, Arleth says, since “they are the ones that ultimately will have to meet all the future expectations in this area.”

    Those future expectations have already led to a new, larger partnership being founded with the aim of putting neutron and synchrotron science to work on industrial problems. The new LINX (Linking Industry to Neutrons and X-rays) consortium comprises three Danish universities and 15 industrial partners, with additional support from Innovation Fund Denmark, the CDI and two Danish regional governments. These organizations have committed to finding solutions to larger and more challenging questions relating to materials in general, including the food and biomedicine sectors. The LINX project is funded for five years, and a parallel LINX Association has also been established to give the project a sustainable long-term future as a platform and mediator for industrial use of neutron and X-ray methods after the public funding runs out.

    Such long-term thinking is critical, in Arleth’s view. “Right now, we have many Danish companies that are highly interested in the opportunities provided by the upcoming ESS and MAX-IV, but they are just not sure how exactly they will benefit from the opportunities provided,” she says. “Presently, only a handful of Danish companies independently conduct experiments at the current large-scale facilities. The LINX project gives us an excellent opportunity to provide qualified answers to many of the ‘how’ and ‘what’ questions the companies have.” By the time the initial five years of funding runs out, she says, they hope to be able to demonstrate a significant increase in the number of Danish companies seeing benefits from applying neutron and X-ray technology to improve their products – plus several examples to inspire others to follow the dairy firms’ lead.

  5. box

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    In small-angle scattering (SAS), a sample is placed in an X-ray or neutron beam (SAXS or SANS, respectively). Typical samples are protein solutions, emulsions or solutions of nanoparticles, detergents or polymers. The sample scatters the beam and the scattered intensity is measured as a function of the scattering angle, typically up to 5°. The detected scattering pattern is related to the Fourier transform of the sample structure, and thus makes it possible to determine the size and shape of scattering particles within the sample on length scales of between 1 and 100 nm (and sometimes even up to μm, depending on the experimental set-up).

    While SAXS is widely available at small-scale lab facilities, SANS is more difficult to come by because it requires a neutron source in the form of a nuclear reactor or a spallation source. Nevertheless, SANS can offer great advantages over SAXS; in particular, the former technique can easily “see” the light elements that are so important for life. These light elements (hydrogen in particular) are either hard or impossible to see with SAXS and other X-ray based techniques, which are more sensitive to heavy elements. SAXS and SANS are often used in combination because they have a different scattering contrast with respect to the sample. Thus, employing both of these complementary techniques often makes it possible to learn about structural details that would not be possible to determine with either technique on its own.

  6. biog

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    Erik Brok and Søren Roi Midtgaard are physicists at the Niels Bohr Institute of the University of Copenhagen, Denmark, e-mail e.brok@nbi.ku.dk

  7. Bringing neutrons into industry

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    Kaoru Sato, Haruo Nakamichi and Hitoshi Sueyoshi explain how neutron science and strong industry–academia links support innovation in Japan’s steel industry

    New heights Advances in steel manufacturing made the construction of the Tokyo Skytree possible. (iStock/winhorse)

    The world produces 1.6 billion tonnes of steel every year. According to analysts at AME Research, this figure could grow to as much as 3 billion tonnes by 2050. For the steel industry, however, improvements in quality matter as much as increases in quantity. The importance of continuous improvement can be seen by comparing the Eiffel Tower with modern steel structures such as the Tokyo Skytree. The former is 324 m tall – a record at the time of its completion in 1889 – and made of wrought iron, a material that begins to deform irreversibly when subjected to stresses of 100–200 MPa (the yield stress). In contrast, the weldable high-strength steel used for the 634 m Tokyo Skytree has a yield stress of up to 630 MPa. Without innovation in steel, such a huge construction would not have been possible.

    The steel industry has long been alert to emerging technologies and keen to benefit from them. The Japanese steel firm Nippon Kokan (a predecessor of JFE, our employer) began using state-of-the-art microbeam analytical instruments such as the transmission-electron microscope (TEM) and electron probe micro-analyser (EPMA) as early as the 1960s. TEMs were used to observe microstructures such as dislocations and small precipitates in steel, while the EPMA was mainly used in the steel-making division for measuring elemental segregation and non-metallic inclusions such as oxides and sulphides. More recently, analyses based on synchrotron radiation have also become widely used for R&D in Japan’s steel industry.

    History lesson

    Compared with X-rays and electrons, neutrons are a less common tool. The relative rarity of neutron beams was, until fairly recently, a high hurdle to their use in the steel industry. Nevertheless, beginning in 2006, JFE began to promote the use of neutron scattering to analyse the microstructures of large-volume steel samples. The history of our approach is documented more fully in a recent report (2017 JFE Technical Report 22 1–5), but the following summary covers a few of the most important points.

    One promising technology for developing high-tensile-strength steel involves dispersing tiny particles (mostly carbides such as titanium carbide and niobium carbide, but sometimes metallic copper) within the steel matrix. These nanometre-sized precipitates hinder the movement of dislocations in the matrix, making the steel strong without sacrificing its formability (at least, not too much). Electron microscopy is a powerful method for directly determining the size and distribution of these precipitates, but the area that can be observed with this technique is limited and the statistical procedures for extrapolating to larger (and thus more representative) areas are tedious. It is also not easy to evaluate nanometre-sized precipitates with chemical extraction methods, since such small particles are often chemically unstable and difficult to collect with filtration.

    Particles (a) The small-angle neutron scattering (SANS) profile of Ti-bearing hot-rolled steel after various heating processes. When combined with knowledge of the shape of the particles (obtained from TEM measurements), this profile made it possible to determine the average size of the TiC particles, as shown in (b). Experiments were conducted at Japan Research Reactor 3 (JRR3). Reproduced with permission from Yasuhara H, Sato K, Touji Y, Ohnuma M, Suzuki J, Tomota Y 2010 Tetsu-to-Hagané 96 545.

    In comparison, we have found that non-destructive neutron measurements possess considerable advantages, combining reliable data from bulk steel with ease of use. In one series of experiments, we used small-angle neutron scattering (SANS) to determine the size of nanometre-sized titanium carbide (TiC) particles within 10 × 10 × 2 mm (thick) sheets of hot-rolled steel. The sample volume for this measurement was about 108 times larger than that used for ordinary TEM thin-foil observations. In the “Particles” figure (a) shows the SANS profile change as a function of heat treatment in this steel. This profile enabled us to determine the average size (b) and the number density of TiC particles. Such knowledge is important because optimizing precipitates is a time-consuming procedure, with numerous combinations of micro-alloying elements and heat treatments that can be tried.

    A promising approach

    The promising nature of our approach led the Institute of Steel and Iron of Japan (ISIJ) to award its 2011 Tarawa best paper award to JFE Steel and our collaborators at the Japanese National Institute for Materials Science (NIMS), the Japan Atomic Energy Agency and Ibaraki University. The easy and precise evaluation of precipitation from bulk steel, without the need for tedious specimen preparations, will certainly promote R&D of new types of steel.
    In addition to studying precipitates with SANS, we are also using neutron diffraction to study steel texture, and to analyse residual stress in welds. The “Welds” figure (right) is an example of a contour plot of (transverse) lattice strain in the weld joint of welded 980 MPa grade steel. At the welding site, there is an increased risk of cracks due to residual stress from the welding and from absorption of hydrogen. Neutron diffraction revealed that the root portion of the weld experiences the highest stress – over 1000 MPa – in the transverse direction. Tensile stress at the root is also present along the weld line and in the plate thickness direction. From this analysis, we were able to infer that high levels of tensile residual stress and the resulting hydrogen accumulation is the key factor for cold cracking. Hence, this neutron-based analysis gave us an important insight into ways of optimizing the weld metal and the welding conditions. As demand for even higher-strength steels continues to increase, the development of steels that are less susceptible to hydrogen embrittlement is vital.

    Welds Strain measurement set-up (a) and a contour plot (b) of strain at various points on a weld in 980 MPa steel. Percentages indicate the deviation of the material’s lattice constant from that of an unstrained sample, and are thus a measure of residual strain ε. Diffraction experiments were performed along the plate transverse (T), the weld line (L) and plate thickness (N) direction of the weld; only data from the T direction is shown here. All measurements were performed using the RESA (REsidual Stress Analyzer) instrument at JRR3. (a) reproduced with permission from Sueyoshi H, Ishikawa N, Yamada K, Sato K, Nakagaito T, Matsuda H, Arakaki Y, Tomota Y 2014 Neutron Network News 24 34 (figure 3); (b) reproduced with permission from Ishikawa N, Sueyoshi, H Suzuki H, Akita K 2011 Quarterly J. Japan Welding Society 29 218.

    Another application of neutron diffraction concerns “retained” austenite in high-tensile strength steel. Austenite is a high-temperature phase of steel with a face-centred cubic structure, and normally it transforms into ferrite (which has a body-centred cubic structure) when cooled. However, with careful control of the heat treatment, areas of steel with high carbon and/or manganese content can be “retained” in the austenite phase even at low temperatures, including room temperature. This is useful because when steel containing retained austenite is deformed, the austenite is transformed into another phase, martensite, creating a strong, ductile material known as TRIP (transformation-induced plasticity) steel that is widely used in the automotive industry. Neutron diffraction is useful for measuring the fraction of retained austenite in steel by volume – something that electrons and X-rays cannot do, because they cannot penetrate very far below the material’s surface. In the future, we hope to fully exploit the potential of neutrons to improve dynamic measurements of phase transformations, and also to analyse hydrogen in steel and perform 3D imaging of embedded defects or inhomogeneities.

    Strong collaborations

    As the application of neutrons to steel research is still relatively new, it is worth taking a closer look at how this research started and how it has been promoted in the steel community in Japan. The research described in the previous section would not have been possible without the efforts of Yo Tomota, a materials scientist then at Ibaraki University (now at NIMS), who pioneered the use of neutrons in steel research, and who organized a research group with JFE Steel under the auspices of the ISIJ. In 2006 the ISIJ chose the development of neutron-based techniques for steel research as its first industry-driven collaborative project. Scientists from other major steel companies and from academia – including both materials and characterization experts– joined in. Over a three-year period, members of the group tested various neutron techniques, including reflectometry as well as SANS and neutron diffraction.
    During the second stage of this group’s work, something very unfortunate happened: the To¯hoku earthquake and tsunami devastated Japan, and the Japan Proton Accelerator Research Complex (J-PARC) and many nuclear reactors had to cease operations. This prompted us to think hard about possible alternative neutron sources. For the third stage of the ISIJ neutron research activity, we strengthened our collaboration between ISIJ members and RIKEN, Hokkaido University and Kyoto University (all of which possess compact or medium-sized neutron sources). In recent years, members of the group have been evaluating the feasibility of using compact neutron sources for steel-related research topics.

    In July 2017 at the International Conference on Neutron Scattering in Daejeon, Republic of Korea, one of us (KS) gave a presentation outlining JFE’s use of neutrons. Afterwards, an audience member observed that it is not easy to stimulate interest in neutrons from industry scientists, and asked why JFE was an early adopter in this area. The immediate answer was that historically, Japanese companies have strong R&D divisions, and the research scientists who work there (in analysis, for example) are used to collaborating closely with academic scientists as well as with process development and steel product development engineers. This means that scientists working in analysis and characterization can understand the languages of both neutron scientists and materials scientists in the company.

    Having scientists who are “multilingual” in both industry and academia, and who can therefore bridge or mediate between each side, is, we believe, the key to a successful synergy. It is worth noting that the steel industry is not the only sector of Japanese manufacturing to place high expectations on neutron technology. RIKEN has provided an excellent summary (www.youtube.com/watch?v=FXLtM6Lqct0) of the ways neutrons are being used in Japanese industry, as well as the fundamentals of neutron science.

    Even so, we believe that further steps are still required for neutrons to become a common measurement tool within industry. Measurements using neutrons are generally easy; however, users often have to wait for several months or even longer for experiments after their proposals are approved. On the other hand, we can use electron microscopes and X-ray diffractometers daily. This lack of accessibility is a huge bottleneck for expanding neutron applications. Recognizing this problem, in 2015 the Japan Science and Technology Agency began an A-STEP (Adaptable and Seamless Technology Transfer Program through Target-Driven R&D), aimed at developing key technologies for compact neutron sources and their industrial applications. This A-STEP includes 10 research themes, and is being supervised by Hideki Yoshizawa of Tokyo University and seven research advisers – including five from industry.

    Achieving goals

    We hope that laboratory-scale neutron measurements will become routine in the near future. In order to achieve this goal, further collaboration between industry and academia is a must. Demonstrating useful results is the only way to ensure that industry will show more interest in neutrons and even invest in such research programmes.

  8. biog

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    Kaoru Sato is a fellow in the JFE Techno-Research Corporation; Haruo Nakamichi is a group leader at the JFE Steel Research Laboratory in Fukuyama and Hitoshi Sueyoshi is a senior researcher at the JFE Steel Research Laboratory in Kawasaki, Japan, e-mail ka-sato@jfe-tec.co.jp