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New views on units

For scientists, the story of metrology has a simple plot: to ensure that standards keep improving. The pound of Imperial France made way for the platinum Kilogram of the Archives in 1799. In 1889 it in turn was traded for the platinum–iridium International Prototype Kilogram (IPK), which this month is on the verge of being replaced by a definition involving Planck’s constant. Each step has made the kilogram standard more secure, serviceable and stable, allowing more precise and definitive research. The latest development, to tether the definitions of all SI base standards to natural constants, seems to bring a triumphant end to this quest.

Philosophers like me look at such stories with different interests. If scientists study the world, philosophers study how scientists study the world. Philosophy, though, is practised in many ways, in what are referred to as the “analytic”, “pragmatic” and “continental” approaches, each of which focuses on different aspects of science (though in practice philosophers may use more than one of these lenses). Not surprisingly, each approach sees different things in the development of scientific standards. There’s more to metrology, it turns out, than simply producing ever-better measuring tools.

Three traditions

As I describe in more detail in my Physics World Discovery ebook Philosophy of Physics, the analytic tradition tends to focus on the logical conditions for science to succeed. Analytic philosophers have, for instance, discussed “stipulative” definitions, in which a term is given meaning by linking it with something else. This is what happens when a unit (such as the kilogram) is linked to a specific artifact (a lump of metal) to create a standard. The process protects the independence of the artifact from the phenomena measured.

In his 1953 book Philosophical Investigations, Ludwig Wittgenstein dramatized the point in a discussion of the International Prototype Metre (IPM), which was then in use and, like the IPK, was stored in a vault outside Paris. The IPM, he said, is the sole object of which we can say, paradoxically yet truthfully, that it is neither a metre long nor not a metre long (a bit like how the definition of a triangle or tree cannot itself be a triangle or tree). That same decade, the German philosopher Hans Reichenbach analysed what would happen if an earthquake destroyed the vault and disfigured its artifacts. The answer, he decided, was “logically very complicated”.

The impending redefinition of the kilogram will, however, mean we lose the independence of measuring standards and measured phenomena. Phenomena tied to Planck’s constant are bound to end up measured by a unit defined in terms of Planck’s constant itself. Though the SI community is content with this, the logical circularity has generated apprehension among some analytic philosophers.

Such circularity will not surprise pragmatists – philosophers more concerned with the practice of science than its logic. The US scientist Charles Peirce, who was also the country’s most original philosopher, was the first to experimentally tie a unit (the metre) to a natural constant (the wavelength of light). His work set in motion events that in 1960, nearly half a century after his death, led to SI, one of whose features was the definition of the metre by wavelengths of a spectral line of krypton.

Peirce developed pragmatism as a theory of thinking in the wake of lessons learned from his metrological experiences. You encounter a problem; you find your inherited concepts and instruments don’t do the work you want; so you study and improve that inheritance. You then use the improved tools to do better research, and so on. All the while you work within a community whose members you have to convince, and who will eventually improve on your work.

Pragmatists focus their attention on the very practice of measuring that analysts seek to bypass, and how that practice affects scientific puzzle-solving. What are the practical dissatisfactions behind the urge to create new standards? How will they affect the community? Does the SI reform truly set its standards outside social and political institutions and democratize access, or reinscribe elitism by making access to standards depend on forefront technology?

As for the third philosophical perspective – the continental – it focuses more on the measurers than on the measuring system or the measuring. A continental approach sees measuring as a special way that humans engage their surroundings. Charles Dickens famously depicted an extreme case in Thomas Gradgrind, the character in Hard Times who in obsessively measuring all aspects of human life loses track of his own; our age has those who obsessively monitor their health biometrically.

SI gets a makeover

Usually, though, measuring involves a momentary objectification of part of the world to foster some broader activity in it – whether it’s homeowners determining what furniture will fit in a house, or physicists determining if a theory accurately characterizes a phenomenon. A continental lens describes this objectification process, how it springs from broader activities, and how it affects them. In the past, improved measurement definitions, while making certain practices more efficient, have sometimes come at the expense of common practices and public understanding. What impact, if any, will the new remoteness of the language of the foundations of measurement have on the everyday perception of scientific practice?

The critical point

The most important impact of the new SI on the philosophy of science, though, may be to inspire philosophers to re-examine these lenses. Why does logical circularity really matter if the important thing is what works for scientists? Is “how it works for the scientific community” the only important issue? Don’t philosophers have to get more up to speed on the practice of technologies involved to judge social and political impact? The new SI may end up doing more than redefining the kilogram: it may also inspire philosophers to reflect on their own assumptions.

US Congress set to welcome eight new members with scientific credentials

Eight candidates with scientific backgrounds have been elected to the US Congress in last week’s mid-term elections. They were part of a significant contribution to the Democratic takeover of the House of Representatives, beating Republican incumbents or winning seats that have long been held by the Republican party. The success of the first-time candidates will roughly double the number of scientifically trained members of the new Congress when it convenes in January.

From the eight candidates, four of whom are women, five trained as engineers while the remaining three have medical backgrounds as a paediatrician, dentist and nurse. “[They] definitely exceeded our expectations,” says Shaughnessy Naughton, president and co-founder of 314 Action – a pressure group founded in 2016 that recruited and trained them. Naughton notes, for example, that Joe Cunningham, a former ocean engineer who is now an environmental lawyer, became the first Democrat in more than 35 years to represent a constituency in South Carolina.

Naughton says that the candidates were successful because they used their scientific and technical backgrounds to talk about issues in their communities from a scientific, problem-solving perspective rather than a political one. “The candidates we supported have a more bipartisan view of government,” she adds.

The difference in politics is that people are out to undo you – not just do better than you. In science, it’s the evidence that counts, not the person. In politics it is indeed the person.
Rush Holt

“The reason they did so well,” says Bill Foster, the Illinois Democrat who remains the only physicist in Congress, “was the outreach against Trump and his non-factual positions.” Indeed, the candidates’ victory was not entirely unexpected according to Rush Holt, a plasma physicist and former Democratic Congressman who now heads the American Association for the Advancement of Science. “Over the past two years I’ve seen it developing,” he told Physics World. “The marches for science in 2017 and 2018 suggested that scientists felt more publicly inclined and that the non-science public was asking them to be more publicly inclined.”

Bringing scientific thinking to government

Yet the transition from science to politics is unlikely to be easy, and according to Foster, the new members will have to deal with a “very irrational place”. “It’s not what’s scientifically true,” he says, “but what you can convince people of”.

That view is backed up by Holt who says the two worlds of science and politics are very different. “Tenacity and hard work, which most scientists bring, are necessary ingredients,” he says. “An ability to frame a problem so that it can be approached effectively and efficiently is useful. But you have to learn some new skills. Holt feels that the hardest adjustment for a scientist going into politics will be psychological. “Science is competitive. But the difference in politics is that people are out to undo you – not just do better than you,” he adds. “In science, it’s the evidence that counts, not the person. In politics it is indeed the person.”

Nevertheless, Foster expects the new Representatives to bring scientific thinking to government. “You have to design logically consistent mental constructs to talk about the world and to make policy decisions,” he says. “That mental habit will bleed into the thought process of Congress generally.”

Neal Lane, a physicist at Rice University who was science adviser to President Bill Clinton, says that while their day-to-day work will be different, there are rewards. “Their fellow Congressmen and Congresswomen will have the benefit of working with colleagues who understand the value of evidence in decision-making and will, I hope, learn from them,” adds Lane.

The Democratic takeover of the House of Representatives will also affect the activities of its committee on science, space, and technology where Texas Democrat Eddie Bernice Johnson is likely to replace Republican and fellow Texan Lamar Smith as committee chair. In contrast to Smith’s skepticism about climate change and other scientific issues, Johnson’s platform includes ensuring that “the US remains the global leader in innovation”, addressing “the challenge of climate change,” and restoring the committee as “a place where science is respected and recognised as a crucial input to good policymaking.”

100% renewable electricity is viable

In their “Burden of Proof” paper last year in Renewable and Sustainable Energy Reviews, Benjamin Heard and colleagues presented their case against 100% renewable electricity systems. As I reported at the time, they doubted the feasibility of many of the recent scenarios for high shares of renewable energy, questioning everything from whether renewables-based systems can survive extreme weather events with low sun and low wind, to the ability to keep the grid stable with so much variable generation. None could meet the set of feasibility and reliability criteria Heard et al. adopted.

Researchers from the Karlsruhe Institute of Technology, Germany, the South African Council for Scientific and Industrial Research, Lappeenranta University of Technology in Finland, Delft University of Technology, Netherlands, and Aalborg University, Denmark, have now hit back with an analysis of hundreds of studies from across the scientific literature to answer each of the apparent issues. They claim that a shift to 100% renewables is technically feasible and economically viable.

Lead author Tom Brown of the Karlsruhe Institute, said: “While several of the issues raised by the Heard paper are important, you have to realize that there are technical solutions to all the points they raised, using today’s technology.” Christian Breyer of Lappeenranta University of Technology added “furthermore, these solutions are absolutely affordable, especially given the sinking costs of wind and solar power”. Brian Vad Mathiesen of Aalborg University commented: “There are some persistent myths that 100% renewable systems are not possible. Our contribution deals with these myths one by one, using all the latest research. Now let’s get back to the business of modelling low-cost scenarios to eliminate fossil fuels from our energy system, so we can tackle the climate and health challenges they pose.”

Looking at the technologies that can make a 100% target realistic, Brown cites the “power to gas” solution of hydrogen or synthetic gas produced with renewable electricity for the “worst case” times when imports, hydroelectric pumped storage reservoirs, batteries and other storage fail to bridge the gap during low wind and solar periods in winter. For maintaining grid stability generally, the report says there are many other technical solutions, including electronics-based solutions, and it presents examples of best practice by grid operators from across the world, from Denmark to Tasmania.

The report adds “from a feasibility point of view, even in the worst possible case that enough [conventional] dispatchable capacity were maintained to cover the peak load, this does not invalidate these [green] scenarios”, since the costs, for example, of a fleet of open-cycle gas turbines (OCGTs), would be relatively low – for example, 7.3% of Germany’s total spending on electricity. But the researchers don’t think a full OCGT fleet would be needed, given the other balancing options, though some OCGTs could be used, fed with biogas or syngas, to help maintain system inertia – or even, at times, just run unpowered to provide grid stability. The team also doesn’t see transmission as a major technical problem; smart grid management can reduce grid stresses, although some grid upgrade would be needed.

General challenge

Moving away from the specific technical areas, the report challenges some of the underlying basics of the approach adopted by Heard et al., who it says often confuse “feasibility” and “viability” in their test criteria, or at least failed to be consistent in their uses of these terms. Certainly, some options may be technically feasible, but not socioeconomically viable, and vice versa, but in reality there will be an interaction as we seek optimals and trade-offs.

Looking in detail at some of the specific “feasibility” criteria used by Heard et al., the report challenges the view that renewables will not be able to meet demand since the latter will always rise. The report suggests that, if we move from thinking about primary energy, which is not very meaningful for renewables, to “end use” energy, given the absence of the large fossil and nuclear thermodynamic conversion losses, supply can more easily match demand, even if the latter does rise. As the researchers say, “primary energy consumption automatically goes down when switching from fossil fuels to wind, solar and hydroelectricity, because they have no conversion losses according to the usual definition of primary energy; ii) living standards can be maintained while increasing energy efficiency; iii) renewables-based systems avoid the significant energy usage of mining, transporting and refining fossil fuels and uranium”.

There are technical solutions to all the points they raised, using today’s technology
Tom Brown

All in all, the report makes a strong technical case for renewables. What’s more, in terms of socio-economic viability, the new system avoids the rising economic, health and environmental costs imposed from using fossil fuels. But even ignoring the avoided climate and air quality costs, the report says, renewables will be economically viable — and cheaper than the current system.

The Heard et al. paper has also been challenged by Australian academics Mark Diesendorf and Ben Elliston, who extend their critique to a paper by Brook and Bradshaw. A core issue is reliability. Diesendorf and Elliston say that the accepted engineering approach is that “reliability is a property of the whole demand-supply system and that a perfectly reliable system is impossible – it would require infinite back-up and hence would have infinite cost”. However, they say that “Brook and Bradshaw confuse it with dispatchability of individual power stations, while Heard et al. confuse it with the presence or absence of base-load power stations in the supply system”.

Dark doldrums

Diesendorf and Elliston do nevertheless admit that there could be problems maintaining supply “during rare periods of several days when there is simultaneously very little wind and solar power over a wide geographic region”. They note that “such periods have been named Dunkelflaute (dark doldrums) in Germany”. However, they say, in most cases, “the critical periods are generally of extent 1–3 h during and around the peaks in demand”.

So the back-up that is required “only has to operate for several hours at a time”. They note that “base-load power stations are not suited to the task”, whereas demand management could help reduce/shift peaks and cheap OCGTs could fill in any gaps. The latter could also maintain supply over longer periods, when other back-up, such as from hydro reservoirs and batteries, was exhausted, for example “if the Dunkelflaute lasts for (say) one week in winter/summer”. Diesendorf and Elliston add that the OCGTs initially “may have to operate on fossil fuels, but in the longer term they can run on renewable fuels (e.g. biofuels, hydrogen, ammonia)”. So their prescription is very similar to that of the Brown et al. study described above.

For good measure, Diesendorf and Elliston also have a sideswipe at the view that “base-load power stations are essential”, noting that “several of the simulation studies achieve reliability with zero or negligible base-load capacity” with “flexible, dispatchable power stations and storage technologies, together with demand response” being needed, rather than inflexible base-load.

In my next post I will look at the base-load issue some more, and at the latest views on P2G (power-to-gas) – the idea of using renewable hydrogen for back-up, as both the above papers proposed, is looking quite good.

MetaboliQs project targets breakthrough in cardiac metabolic MRI

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Two of Europe’s leading research groups in hyperpolarized and cardiovascular MRI — ETH Zurich in Switzerland and the Technical University of Munich in Germany — have joined MetaboliQs, the project funded by the European Union (EU) that is due to continue until the end of 2021.

The project is part of Quantum Flagship, which has received funding from the EU’s Horizon 2020 research and innovation program. The other partners are the Fraunhofer Institute for Applied Solid State Physics (IAF), Bruker BioSpin and NVision Imaging Technologies (all from Germany), Element Six (the UK-based supplier of synthetic diamonds) and the Hebrew University of Jerusalem in Israel.

“This initiative intends to place Europe at the forefront of the second quantum revolution, which is now unfolding worldwide. It aims to bring disruptive quantum technologies to the scientific arena and to society in general by bringing forward new commercial opportunities addressing global challenges, providing strategic capabilities for security and seeding yet unimagined applications for the future,” according to a statement issued by the team.

The ability to personalize cardiovascular medical care and improve outcomes will require characterization of the heart, other organs, and the characterization of tumours at the molecular level, the statement continued. MetaboliQs will combine diamond-based quantum sensing and medical imaging to foster the molecular understanding and personalized care of cardiovascular diseases.

“Because of their limited sensitivity, even the most expensive MRI scanners (with the strongest magnets) cannot detect and visualize molecular and metabolic activity in the heart with sufficient sensitivity and specificity,” the project’s organizers noted. “To this end, emerging hyperpolarized MRI techniques play a pivotal role as they allow increasing the sensitivity of MRI by up to five orders of magnitude.”

The hyperpolarization process takes a very long time (90 to 180 minutes per procedure), is extremely costly and cumbersome (more than 1.75 million euros initial cost), and requires temperatures below -270 °C. The MetaboliQs project, therefore, aims to enable a new method for MRI by leveraging new advances in quantum physics.

What is hyperpolarized MRI?

Hyperpolarized MRI allows imaging and visualization of key metabolic substrates in the heart and other organs, such as the kidney and liver, via hyperpolarization of nuclear spins of substrates that are natural to the body and nontoxic, allowing a number of important metabolic reactions to be tracked noninvasively, the researchers explained.

Hyperpolarization can dramatically increase the signal-to-noise ratio in MRI, and is being applied to small injectable endogenous molecules that can be used to monitor transient in vivo metabolic events in real-time. The emergence of hyperpolarized carbon-13-labelled probes — specifically C-13 pyruvate — has enabled monitoring of core cellular metabolic events. Neuro-oncological applications have been demonstrated in preclinical models, and they might transform MRI in the future, wrote New York neuroradiologist Vesselin Z. Miloushev, in an article in Topics in Magnetic Resonance Imaging about the technique.

“The promise of hyperpolarization technology is to harness the unique ability of nuclear magnetic resonance spectroscopy to distinguish chemical moieties on the basis of chemical shift and to characterize their dynamic properties in vivo,” he noted. “Many more applications are envisioned that can harness the unique power of this technology.”

Hyperpolarized carbon-13 MRI is a functional technique that works by probing perfusion and metabolism using injected substrates. It provides chemical as well as spatial information, and is being used to probe the activity of specific metabolic pathways.

The technology will enable a previously unachievable, highly sensitive quantification of metabolic activity, paving the way for precision diagnostics and better personalized treatment of cardiovascular diseases, the MetaboliQs statement added. For example, it will become possible to distinguish patients who are most likely to benefit from invasive or pharmacologic cardiac interventions from those who will need other medical treatment, and to accurately diagnose patients at the disease’s early stages.

“The project will leverage the transformative features of diamond nitrogen vacancies, such as high quantum coherence and quantum control, to offer a breakthrough in cardiac hyperpolarized MRI: a low cost and high-throughput diamond polarizer that can be used with any MRI scanner and show results within minutes instead of hours required per procedure,” the group stated. “This unique utilization of quantum coherence is made possible by new technology to atomically engineer diamond material (quantum-grade diamond), including C-12 isotopic purification, precise control of nitrogen defect concentration, and nanofabrication of the diamond surface.”

Achieving the consortium’s goals

The MetaboliQs consortium, through its combination of leading research institutes and innovative companies, provides the end-to-end expertise required to reach the ambitious objectives of the project and develop breakthrough capabilities in hyperpolarized MRI for cardiovascular applications, according to the statement.

The research of the Fraunhofer IAF is organized into four specialist departments: epitaxy, technology, microelectronics and optoelectronics. There is a close exchange between these units as well as cooperation across departments in most research projects. All departments are organized into four to six teams. Additionally, there are two infrastructural departments at the facility (administration and technical services) as well as two groups (information technology and quality management).

To target industry clients and partners, political actors, as well as partners in science, Fraunhofer IAF focuses its research activity on five business units: high-frequency electronics, power electronics, photodetectors, semiconductor lasers, and diamond devices.

This article was originally published on AuntMinnieEurope.com © 2018 by AuntMinnieEurope.com. Any copying, republication or redistribution of AuntMinnieEurope.com content is expressly prohibited without the prior written consent of AuntMinnieEurope.com.

Cool innovations for clean energy

Although climate change is undoubtedly an urgent problem for humanity, there is at least one climate-related context where it’s appropriate to use the word “bullshit”. That’s when the subject is methane. When bacteria break down the pungent by-products of cattle farming, methane is released in vast quantities. Since methane is a greenhouse gas around 30 times more potent over 100 years than the main warming villain, carbon dioxide, these agricultural emissions pose a sticky environmental problem.

For entrepreneur Chris Mann, though, they are also an opportunity. When he moved to rural Cornwall in south-west England, he learned that local farmers sometimes feed slurry waste into anaerobic digesters (ADs). These devices burn the methane they produce – turning it into less potent carbon dioxide – and generate electricity. However, most farmers are not close enough to connections that can fully accept that power. One of Mann’s neighbours, for example, devised a cheap AD, but could only sell a fifth of the electricity he produced.

That waste inspired Mann to co-found Bennamann, which develops cryogenic techniques for storing methane so that it can be used to generate energy where and when it is most needed. But the story of Mann, his company and his neighbour’s cow dung is just one of several ways in which cryogenics might help clean energy fit into existing electricity-generation systems.

It is well known that both solar and wind power don’t necessarily generate electricity when people want to use it. “An important part of the electricity system is missing,” explains Gareth Brett, chief executive officer of London, UK-based Highview Power, which is also developing cryogenic energy storage (CES) technologies. “To balance the grid, we need long-duration storage – four hours, or maybe eight.”

Batteries are good for high-power, short-duration storage, but become too expensive and large for longer durations, Brett asserts. Although it is only one of many possible solutions being explored by companies, academics and government bodies, CES does offer certain advantages. In particular, CES systems can be very compact, with liquid air being around 800 times denser than the gas. Hence, CES systems make it possible not only to store renewably generated energy, but also to supply it at the right time and in the right place. That includes in vehicles as they travel, or in remote locations.

How it works

Mann compares cryogenic cooling to a “pressure cooker in reverse”. The main idea is to slow the rate at which gas boils off by lowering its pressure and temperature, typically to below 125 K. To minimize the energy required, engineers seek to keep components of a gas’s internal energy – the entropy and/or enthalpy – constant. Ideally, there would be no transfer of heat to or from the surroundings. In practice, even the best systems never quite achieve this. Decades of R&D have nevertheless produced efficient, well-established liquefaction cycles for cryogenically cooled gases, with multiple stages of compression and then expansion into low-pressure chambers.

Cleaning up: Liquid-nitrogen-powered engines could replace diesel for some applications, reducing particulate pollution in cities and along transport corridors. (Image courtesy: Dearman)

One of these processes, the Claude cycle for making liquid air, is central to Highview Power’s business. Highview exploits cheap electricity – usually at night-time – to power a modified Claude cycle, liquefying air at around 80 K. This liquid air is stored in low-pressure, vacuum-insulated tanks, like those in the industrial-gas sector, Brett explains. Then, when electricity demand is high, they pump up pressures and evaporate liquid air through a heat exchanger. There, heat from ambient air or hotter air – released either by the refrigeration cycle itself or by a neighbouring industrial process – turns liquid air back into gas. That expansion drives an electricity-generating turbine.

Brett claims that Highview’s liquid-air energy storage (LAES) system offers a storage density and self-discharge losses similar to those of lithium-ion batteries, but without batteries’ potentially hazardous electrolytes and heavy metals. The system also exploits relatively simple and readily recyclable steel systems already used in industry. Companies involved in electricity generation, or any large process plant, have the know-how required to maintain Highview’s LAES systems, Brett says. These systems have “about the same longevity” as other grid-scale power plants, he adds. Such claims are now being tested: Highview opened a 5 MW/15 MWh demonstration plant in Bury, UK, in June 2018, following an earlier 350 kW/2.5 MWh pilot. The company also hopes to announce a 50 MW/250 MWh system for an undisclosed customer “in the next few months”, according to Brett.

Cold capture

Like Brett, Judith Evans is interested in CES systems that mainly use existing technologies. As a refrigeration engineer at London South Bank University, Evans co-ordinates the European Union-funded CryoHub project, involving partners from five countries. They are collaborating to build a demonstration system that integrates renewable energy generation and CES with a large cold store owned by Frigologix, a storage and distribution firm based in Lommel, Belgium. The benefits of integrating with a cold store stem from the opportunity to recycle cold and heat. By itself, CES generally only offers 25% “round trip efficiency” – the ratio of energy generation to consumption. Adding a thermal store to capture the cold generated when the liquefied gas evaporates can at least double this.

Whereas Highview reuses its waste cold during the next liquefaction cycle, CryoHub seeks to exploit it in cold storage. A major goal of CryoHub, therefore, is to improve existing cold-storage systems. “One issue is cost,” Evans says. “You can make an amazing thermal store if you’re prepared to put a lot of money into it, but to make an economic case you have to reduce the cost as much as possible.” According to the CryoHub team’s models, which are due to enter testing soon, the very best round-trip efficiency could be as much as 80%. This would be challenging to achieve in practice, but some improvements are definitely necessary, Evans says. “If you’re going to compete purely on energy storage, you have to get your round-trip efficiency as high as you possibly can,” she explains.

On the road

Liquid air produced for cooling can also be used for other purposes. Evans notes that one CryoHub partner, the Paris-based industrial gas firm Air Liquide, already uses cryogenics in vehicles or for transporting goods at multiple temperatures. Currently, they use liquid nitrogen, but might be able to convert systems to liquid air.

Another company with an interest in putting liquid-nitrogen cooling on the road is Dearman, a London-based firm set up in 2011 to exploit the liquid-nitrogen-powered engine invented by founder Peter Dearman. “You could regard liquid nitrogen as a vector for moving grid energy onto a moving truck,” says Chris Owen, Dearman’s head of cryogenics. “If you look at the overall cycle, including the production of liquid nitrogen, we release roughly a tenth of the carbon dioxide as a diesel engine on a truck.”

Of course, this calculation relies on using renewable energy to liquefy the nitrogen. As with everything in the energy business, there is no free lunch. A Dearman engine generates a maximum of 214 Wh/kg from liquid nitrogen, while the liquefaction process itself requires 400 Wh/kg. In Dearman’s experience, making that loss financially viable means producing liquid nitrogen only when the cost of renewable energy dips to half the peak electricity cost for the day. “It’s finding the right environment where power price swings are as big as we need them to be to make it profitable,” Owen says.

With this in mind, Dearman is currently focusing on replacing the diesel engines found in trucks’ refrigeration units. Such engines are almost unregulated, and contribute greatly to particulate air pollution in cities. “The city of Los Angeles could lose a third of its particulate load if it replaces its current refrigeration unit engines with Dearman engines,” Owen says. Dearman has supplied engines for this application to UK food retailers and producers including Sainsbury’s, Marks and Spencer and Unilever. It also hopes to extend the approach to train and bus air conditioning.

Reducing greenhouse gases

Back in Cornwall, Mann and his company also hope to displace dirty diesel. But they want to use cryogenic biomethane rather than liquid nitrogen, as fuel for the trucks themselves rather than for the refrigeration units they carry. Liquid natural gas (LNG)-powered trucks already offer some local pollution-reduction benefits, but extracting and burning this fossil fuel still adds to overall greenhouse-gas emissions. Moreover, as the stored fuel expands, United Nations regulations allow trucks to vent their fuel tanks after five days, bringing flammability hazards as well as threats to the climate.

Bennamann has therefore developed a cryogenic storage system that never vents to air. Instead, it uses released methane to power an engine or fuel cell to sustain low temperatures. This contained pressure release enables much lower storage pressures than for LNG. Tanks can therefore be larger, and the methane kept cooler, making it denser. This, in turn, lets trucks carry more cryogenic fuel, enabling them to travel between 300–500 km on a single tank, Mann says. “This is where the market needs to be to compete with diesel,” he adds.

Bennamann’s technology also offers permanent storage tanks for farms, and their prototype has enabled Mann’s neighbour to sell all his AD-powered electricity, rather than just some of it. But Mann is more enthusiastic about fuelling trucks with gas from cow slurry. “If you do that, then the biomethane has significantly more value,” he says. “You don’t need a subsidy to make it profitable. I think it’s revolutionary for small farms.” However, Mann estimates that the company’s products won’t be available for two years.

On its own, even a revolution in cryogenic gas technologies would not resolve the enormous challenge that climate change poses to humanity. Dearman’s Owen, however, notes that they can definitely contribute. “It’s a problem we all accept is going to be solved by a lot of small changes rather than one big one,” he says. Replacing diesel used in refrigeration engines “is one small change that moves us in a dramatically right direction”, he adds. CES and biomethane truck fuel could well provide a similar nudge. After all, like slurry in a digester, every little bit helps.

Optical micromirrors reveal the secrets of cell membranes

Progress in understanding the lipid bilayer – an ingenious two-molecule thick oily barrier that protects all living cells, including our own – has been dramatic over the past 100 years. But there are still puzzles to be solved. In particular, biologists are keen to discover more about the mysterious proteins that exist inside the lipid bilayer. These chains of amino acids assemble into folded structures that change the behaviour of the cell membrane – allowing, for example, the selective passage of salts and sugars in and out of a micro-organism.

In fact, cell membranes are home to a variety of proteins that are essential for life to proceed, including channels, transporters, pumps, and receptors. These forms are relatively well known, but what isn’t understood is how these membrane proteins, which are oily themselves, navigate the oily lipid bilayer to go about their work.

The first step for scientists is to figure out the thermodynamic rules that govern protein assembly in membranes. And research groups such as Janice Robertson and her team, formerly based at the University of Iowa and now at Washington University in St Louis, are using cutting-edge microscopy tools to come up with the answers. “The major goal of my research is to answer the question: why do greasy membrane proteins choose to interact with other greasy proteins, instead of the greasy lipids in the surrounding cell membrane?” she explains.

Optical solutions for biological problems

One of the most useful techniques for looking inside the lipid bilayer is total-internal-reflection fluorescence microscopy (TIRF). The optical arrangement in these systems generates a localized illumination of molecules just above the surface of a glass slide that is situated above an objective lens. Using fluorophores – chemicals that fluoresce when excited by light – as markers, researchers can examine how populations of molecules inside the lipid bilayer change in response to different conditions.

A number of different microscope configurations are available, but what’s special about Robertson’s set-up is the use of micromirrors to direct incoming laser light into the microscope objective. The angle of incidence is adjusted so that the beam internally reflects at the sample interface, sending an evanescent wave into the sample that decays over a distance of a few hundred nanometres. This yields the narrow excitation volume that is ideal for looking at single molecules.

Buying the microscope was a huge time-saver and it meant that we could benefit from all of the engineering and stability that had been designed into the system
Janice Robertson, Washington University in St Louis

The use of micromirrors, compared with the more usual multi-wavelength dichroic filters, improves the signal-to-noise ratio that can be achieved with TIRF microscopy. Two micromirrors are placed underneath the microscope objective, one directing laser light into the lens and the other guiding the radiation out, leave plenty of space around the sample stage – which is useful for placing other equipment such as micropipettes or additional optical detectors. Also, the mirrors are optically compatible with a range of different laser wavelengths, which means that Robertson and her team can use different colours of light to selectively excite a series of fluorophores in a sample without swapping components in the optical path.

“I first learnt about this microscope when I was doing my post-doctoral training and collaborating with researchers at the Gelles laboratory in the Department of Biochemistry at Brandeis University,” says Robertson. “They had built their own microscope – an objective-based TIRF that used micromirrors instead of a dichroic mirror to direct the excitation beam.” This set-up allowed the scientists to collect a strong signal from their sample while reducing background noise.

Flexibility benefits research

When Robertson was in a position to set up her own lab at the University of Iowa, she knew exactly what she wanted from a TIRF microscope and looked for a vendor that could supply a micromirror-based system. “The big advantage of the Mad City Labs MicroMirror TIRF microscope is that it allows you to have the advantages and the flexibility of a home-built system,” she comments.

In principle, her group could have also assembled a microscope from scratch, but the researchers wanted to get up and running as quickly as possible so that they could continue their experiments. “Buying the microscope was a huge time-saver and it meant that we could benefit from all of the engineering and stability that had been designed into the system,” Robertson points out.

After five years at Iowa, Robertson had the opportunity to expand her research again – this time moving to Washington University in St Louis. It meant breaking down the microscope and reassembling it in her group’s new labs, but it also gave the team the chance to further update the apparatus.

The latest set-up features Mad City Labs’ newest MicroMirror TIRF microscope design. The updated design makes the system even more flexible, and allows users to switch easily between different illumination modes (including TIRF) thanks to an automated module. “It’s really useful to have that versatility to flip between studying whole-cell or liposome fluorescence, as well as single-membrane protein molecules, in the same samples,” Robertson comments.

Molecular interactions brought into view

Using the system, the team has been continuing to study the reactions of membrane proteins to shed light on what makes these molecules self-assemble, fold and bind to one another in the lipid bilayer. In water, explains Robertson, protein folding and assembly is driven by strong differences between the protein (oily) and the solvent (water), but these conditions don’t exist within the lipid bilayer and yet protein folding and assembly persists.

To investigate this question, the Robertson laboratory is studying the equilibrium association reactions of proteins inside the membrane. By looking at probability distributions of protein assemblies in data generated by the MicroMirror TIRF microscope, the group has been able to follow populations of transporter proteins as they equilibrate inside membrane layers. “We can do full accounting of the protein into the liposomes, which takes us a step closer to understanding the binding process and the thermodynamic driving force for assembly,” says Robertson.

The data collected can also include movies. The team’s new set-up features two cameras – a charged-coupled device for capturing regular micrographs and a CMOS camera to provide enhanced time resolution – which makes a powerful combination. “It’s possible to look at a lipid bilayer on the glass and see single-molecule diffusion of both the lipids and different membrane protein components, allowing us to potentially visualize those reactions in real time,” Robertson explains.

Robertson also values the support provided by the community. “It’s a very open field and people are willing to help each other, which helps a biologist like me,” she says.

Visit the Mad City Labs website for more information on its MicroMirror TIRF microscope.

Flood models validated in Africa

Flood models tested in the first collective validation captured between 52 and 97% of flooded areas for two flood events and three areas in Nigeria and Mozambique. This result was “better than expected”, according to the research team.

“These models have shown a level of performance that allows them to be used for large-scale questions, like identifying the regions of highest flood risk globally,” says Mark Bernhofen of the University of Leeds, UK. “The majority of the models performed fairly well.”

In the decade leading up to 2015, floods killed an estimated 157,000 people worldwide, and affected 2.3 billion in total. As climate changes, the number of people exposed to river flooding over the next three decades is likely to rise by over 30%.

Every model of climate impact depends on a broader climate model to drive it. Whereas climate models have been compared and validated since the late 1980s, flood models have existed only for the last decade or so. Until now, their validation has taken place individually, using different methodologies. “The different results are difficult to compare,” says Bernhofen.

To overcome this problem, Bernhofen and colleagues from the UK, Japan, the Netherlands and Italy tested six global flood models using the same technique, for flooding in Lokoja and Idah in Nigeria in 2012, and Chemba in Mozambique in 2007. The researchers compared the models’ predicted flood areas against historical satellite data over millions of pixels, each about 90 sq. m in size.

The 2007 floods in Mozambique affected 130,000 people while those in Nigeria in 2012 affected 4 million people.

According to a widely used “critical success index”, which rates a model from zero – worst at representing reality – to one, the six flood models in the validation ranged from 0.45 to 0.7. This was better than the team expected.

The models performed best for the 2012 flooding in Lokoja, a city at the confluence of the Niger and Benue rivers that has a well-defined floodplain. The worst performance was for the same flood event downstream from Lokoja in the Idah region, where the floodplain is large, flat and has many interconnecting channels. “That makes modelling the flow of water a lot more complicated,” says Bernhofen.

Although the global flood models are relatively young, Bernhofen believes they’ve benefitted from the many decades of detailed flood modelling at smaller scales. He hopes this analysis highlights the effectiveness of the validation procedure, and helps people “make an informed decision about the most appropriate model to use and where”.

“The goal now is to expand this validation to include more flood events in more regions, and broaden the skills-measures we use, so that we can get a truly worldwide view of the performance of these global flood models,” he says.

The team published the study in Environmental Research Letters (ERL).

Encrypted quantum keys sent a record-breaking 421 km in optical fibre

Encrypted quantum keys have been sent across a record-breaking 421 km of optical fibre at the fastest data rate ever achieved for long-distance transmission. Alberto Boaron and colleagues at University of Geneva and ID Quantique in Switzerland and Corning in the US achieved this feat by modifying the detectors used for quantum key distribution (QKD) to minimize noise. Their experiment represents a significant advance in the secure exchange of quantum information.

QKD uses the laws of quantum mechanics to ensure that an eavesdropper cannot intercept a cryptography key without alerting the sender and recipient.

Over the last decade, rapid advances in QKD have made the technology increasingly attractive for parties including banks and governments desiring fast, secure exchanges of sensitive information. Despite its progress, however, QKD still faces significant barriers to improvements in the speeds and distances over which encryption keys can be exchanged.

At the heart of the problem are the natural thermal fluctuations found in the detectors picking up key-carrying photons, as well as blackbody radiation from the optical fibres transporting the photons. If left unchecked, these fluctuations will cause detectors to read out photons mistakenly, resulting in erroneous “dark counts”. The number of dark counts increases exponentially with transmission distance, greatly reducing the system’s signal-to-noise ratio, and subsequently, the rates at which encrypted quantum keys can be transmitted.

Spiral nanowires

Boaron’s team modified the design of their detectors to reduce noise in the system. Their setup consisted of superconducting nanowire single-photon detectors arranged in spiralling patterns on a flat surface. Once in place, the nanowires were cooled down to 0.8 K to further minimize their thermal fluctuations, while the optical fibres transporting the key-carrying photons were cooled to 40 K to reduce their blackbody radiation.

With these adaptations in place, the team observed a dark count rate of just 0.1 Hz in their detectors – two orders of magnitude lower than achievable with current commercially-available nanowire detectors. In practice, this improvement allowed the researchers’ apparatus to achieve key rates 100 times higher than those demonstrated in previous studies for lengths of optical fibre between 251 km and 404 km. Key rates also remained positive over a distance of 421 km – the longest QKD transmission distance achieved so far. In addition, the results remained highly stable over time, with Boaron’s team observing consistent key rates over experimental running times of up to 24 hours.

Despite these improvements, the team’s conventional QKD setup is not as secure as “measurement-device-independent” QKD – which was used to set the previous record of 404 km. However, further improvements to the simpler approach taken by Boaron and colleagues could make conventional QKD the preferred method for some applications including digital telephony in metropolitan networks.

The research is described in Physical Review Letters.

MRI-guided cryoablation safely freezes tumours in the spine

Treatment of epidural tumours located in the spinal canal can be highly challenging, due to the risk of causing irreversible damage. To address this challenge, a medical team at Brigham and Women’s Hospital and Dana Farber Cancer Institute have performed a study showing that MRI-guided cryoablation is feasible for treating such epidural tumours. After cryoablation, both patients in the study experienced successful decompression of the tumour away from the spinal cord, regrowth of previously eroded bone around the spinal canal, and reduction or elimination of the risk of becoming paralysed by the cancer (Am. J. Roentgenol. 10.2214/AJR.18.19951).

When a tumour compresses the spinal cord, previous options treatment included spinal decompression, a surgical procedure to relieve pressure, spinal decompression and radiotherapy, stereotactic radiosurgery, or laser interstitial thermal therapy. Each of these treatments, however, is associated with serious risks. Some patients are unsuitable candidates for surgery, and some who undergo it may not recover rapidly, delaying radiotherapy. Radiation dose delivery may be limited by the tumour’s proximity to the spinal cord, therefore reducing the effectiveness of radiotherapy. And ablative techniques such as laser interstitial thermal therapy may cause permanent neural burn injury.

“The main advantage of cryoablation over heat-based ablation modalities such as radiofrequency ablation is visualization of a distinct edge of ablation, which can be monitored as a black ovoid region on standard MRI,” the authors state. “Another advantage of cryoablation … is the reduced risk of injuring adjacent structures, such as carotid artery walls, leading to dissection and blowout, or central nervous structures, which have no ability to regenerate.”

Cryoablation also enables a patient to regrow previously eroded bone and regenerate cortex and marrow architecture, which does not happen after surgical resection or heat-based ablative treatments.

MRI provides excellent visualization and nearly real-time imaging of the tumour, the ablation zone and involved neural structures. It is also better than CT at visualizing the cryoablation zone and the adjacent spinal cord as, with CT, the high radiodensity of bone can obscure the low-radiodensity ice ball. Unlike CT, MRI can also be used to accurately image epidural tumours invading or compressing central nervous system structures.

The MRI-guided cryoablation process

Lead author Thomas Lee, a neuroradiologist at Brigham and Women’s Hospital, told Physics World that the hospital’s MRI-guided operating suite was made possible through the vision of the late neuroradiologist Ferenc Joelsz, known for his breakthrough contributions in image-guided therapy.

The Advanced Multimodality Image Guided Operating (AMIGO) suite, where procedures are performed, is a clinical translational test-bed for research of the National Center for Image-Guided Therapy.

The cryoablation procedure often begins by using CT guidance to drill into the bone for cryoprobe placement. The authors note that MRI can be used alone to place the cryoprobe if bone along the necessary path has already been completely eroded. Once the cryoprobe is in position, the team employ MRI to monitor growth of the cryoablation zone using standard axial and sagittal T2-weighted MR images. These can be acquired as rapidly as every 0.5 s, although are usually tailored to 1 min sequences in a 3T MRI.

Treatment comprises an initial cryoablation freeze for approximately 10 min, followed by a 5-min active thaw and a second freeze. The total procedure time varies between a couple of hours to an entire day depending on the complexity of the cancer. “Much of the time is in preparing the patient for the operating room and placing the cryoablation probe to avoid critical structures,” Lee explains. “This is usually an outpatient procedure, and patients can leave the hospital several hours after its completion.”

Principal investigator Thomas Lee demonstrates an active cryoprobe that had just been tested in water to ensure formation of a ball of ice at the tip. (Courtesy: Thomas Lee/ Brigham and Women’s Hospital)

Lee and his team have now performed 11 MRI-guided cryoablation procedures for spinal canal decompression, and a total of 76 MRI-guided cryoablations in the head, neck and spine. He believes that Brigham and Women’s Hospital is the only hospital in the world currently performing MRI-guided cryoablation for spinal canal decompression.

“In addition to disease affecting the spinal cord, we have started treating disease affecting the brain,” he says. “It is an exciting new field where disease affecting the brain or spinal cord and minimally invasive treatment can be seen together on MRI to help patients. Basically, people about to be paralysed by cancer can now have hope that their cancer can be frozen with a needle, and that they can walk out the same day knowing that within the next month the cancer will die and their spine will regenerate on its own.”

Megawatt laser beacon could communicate with aliens

A bright laser beacon that announces our presence to extraterrestrial civilizations could soon be achievable, new research suggests. Calculations done by James Clark and Kerri Cahoy at the Massachusetts Institute of Technology suggest that current and near-future technologies could be used to produce light intense enough to be detectable to extrasolar astronomers as distant as 20,000 light-years away. The duo’s research also sheds light on how we could detect signs of intelligent life in star systems beyond our own.

For decades, some in the astronomy community pondered what would be the best way of communicating with intelligent alien life on distant planets. Once a purely academic question, the desire to communicate has been heightened recently by the ongoing discovery of large numbers of exoplanets orbiting stars other than the Sun.

Recently, two nearby exoplanets have proved particularly attractive for such efforts. These are Proxima Centauri b, a planet which lies in the habitable zone of our closest star just 4 light-years away; and the TRAPPIST-1 system, which at a distance of 40 light-years is believed to contain three potentially habitable exoplanets, are currently viewed as our best hopes for receiving replies to our messages.

Focussing on aliens

An important challenge is how to create a signal that stands out from glare of the Sun. In their study, Clark and Cahoy set out to show that the odds of such signals being detected could be greatly improved by focusing megawatt-power lasers using large telescopes. To do this, the researchers first calculated the resulting intensity when infrared lasers of various different powers were combined with telescopes of varying aperture sizes. They then calculated the resulting apparent magnitudes of the beams when viewed at varying distances from the Sun.

Clark and Cahoy discovered that a 2 MW signal fired through a 30 m telescope would have a large enough magnitude to clearly stand out from the Sun’s natural variation in infrared emissions to astronomers on Proxima Centauri b. At the same time, a 1 MW laser combined with a 45 m telescope would not only be clearly detectable in TRAPPIST-1, but would be visible at 20,000 light-years away – covering the entire Orion Arm of the Milky Way. The beams would also be broad enough to encompass the entire habitable zones of more distant stars, and could carry data at rates of several hundred bits per second, allowing for exchanges of complex messages.

Significantly, Clark and Cahoy showed that these feats are all achievable within our current grasp of both laser and telescope technologies. While the US Air Force has already demonstrated its megawatt Airborne Laser, both the 29 m Giant Magellan Telescope, and the 39 m European Extremely Large Telescope, are currently under construction in Chile, each due to begin operation in the mid-2020s. With these technologies within practical reach, it now seems that communicating with our galactic neighbours could be easier than we realized.

The research is described in The Astrophysical Journal.

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