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Panel calls for more research into carbon-capture technologies

Avoiding global temperature rises of just a few degrees in the coming decades will require the use of technologies that directly remove greenhouse gases from the atmosphere. That is according to a new report released on 24 October by the US National Academies of Sciences, Engineering and Medicine, which warns that even having a carbon-neutral energy sector would not be enough to reverse potentially catastrophic alterations to the Earth’s climate.

The report – Negative Emissions Technologies and Reliable Sequestration: A Research Agenda – states that to meet the Paris Accord goal of limiting anthropogenic warming to 1.5-2.0 °C, greenhouse-gas emissions will have to fall from 50 gigatonnes of equivalent carbon dioxide (GtCO2e) today to less than 20 GtCO2e by 2050 and zero by 2100. The 17-strong committee that wrote the report found, however, that 10-20 GtCO2e of emissions – mostly from agriculture and air travel – could not be eliminated, warranting the need for a widespread implementation of negative-emissions technologies (NETs).

The report states that some forms of NETs are ready for upscaling such as reforestation as well as “bioenergy with carbon capture and sequestration”, in which plant-based materials are used to produce electricity and carbon dioxide produced is captured and stored underground. However, environmental scientist Stephen Pacala from Princeton University, who chaired the committee that wrote the report, points out that the environmental and social impact of such methods could have serious consequences. “One creates major land transformations at one’s peril, so we did not want to do that,” says Pacala.

Showing promise

The committee instead outlines other NETs that show promise with fewer potential side effects. One is the mineralization of CO2, in which it is made to bond with reactive minerals in rocks. There are, though, some drawbacks with the technique particularly as inserting a CO2 subsurface into formations could quickly clog up the rock surface or – as is observed in nature – cause exothermic reactions that fracture the rock and actually enhance the sequestration.

To tackle these issues, the NASEM report proposes funding a 10-year R&D programme, which would include a $10m field experiment in peridotite rock to better understand the technique. “With this technique we are talking about [removing] hundreds of millions of tonnes of CO2,” says geochemist Peter Kelemen from Columbia University who co-authored the report. “The research challenge is to get into the regime whereby the process keeps the pour space open by creating new fractures and extending existing ones.”

Another possibly “revolutionary” NET method, according to the report, is the direct capture of CO2 from the air. This would involve capturing ambient CO2 on a substrate and then releasing it into a storage reservoir. The report highlights cost as the major obstacle for this technique and proposes the construction of a $100m air-capture demonstration plant that will sequester more than 10 000 tonnes of CO2 each year.

Klaus Lackner, a physicist who leads the Center for Negative Emissions at Arizona State University and was not involved with the NASEM report, says that because past emissions need to be dealt with, the “time has come to invest in and deploy NETs”. But he expects the price tag for direct air capture of CO2 to decrease in future similar to how photovoltaic technologies have reduced in cost. “I don’t see that there are physics parts that you cannot get the cost below a certain amount,” says Lackner.

Ancient enzyme resurrected for commercial biocatalysis

By “resurrecting” the genetic sequence of an ancestral form of the technologically important P450 enzymes, researchers at the University of Queensland in Brisbane, Australia, have succeeded in significantly improving their thermal stability. The enzymes can now be made to be robust to temperatures as high as 66°C and better resist solvents compared to the non-stabilised forms. The new technique might be applied to a whole range of other enzymes and proteins and could revolutionize commercial biocatalysis. The stabilised enzymes will also be ideal for studying the fundamental function and structure of proteins to better understand how they work.

Enzymes will play a crucial role as catalysts in the emerging bioeconomy of the 21st century, says Elizabeth Gillam of the School of Chemistry and Molecular Biosciences at the University of Queensland, who led this research effort. The problem is that naturally occurring enzymes are often not very stable at the elevated temperatures and over the long time periods routinely employed in industrial processes. “It is difficult to design an enzyme so that it is thermostable because proteins are very complex and we simply don’t know enough about how they work to design them from scratch, despite much intensive and costly wet-lab research over the past decades.

“By stabilising cytochrome P450 enzymes, which are involved in the production of many naturally occurring drugs, flavours, fragrances, pesticides, hormones and other interesting chemicals by bacteria, plants and animals, we can now conceive of them as being used as ‘off the shelf’ catalysts for the first time. This will accelerate the field of biocatalysis and allow chemical processes to become more efficient and environmentally friendly.”

Ancient enzymes were more thermostable

In the past, Earth was much hotter than it is today and in pre-Cambrian times, for example, ocean temperatures were as high as 60°C or more. The enzymes in any organisms around at this time (which were mainly primitive marine microorganisms such as bacteria and archaea) would have had to tolerate these temperatures. “In more recent times, such as when the first complex animals and plants, and ultimately vertebrates like us evolved (around 450 million years ago), temperatures were thought to be much milder (within about 10 degrees of those we enjoy today). There was therefore no need for enzymes to be so thermostable.

“To ‘resurrect’ ancestral more thermally stable P450 enzymes that existed at the time the first vertebrates began to appear, we began by obtaining all the gene sequences of this enzyme that we could and worked out the similarities between their sequences and the evolutionary relationships between them all,” she tells Physics World. “We then determined the most likely sequence of their common ancestor (a best guess at the gene from which they all evolved) using a computer algorithm. We then had this synthesized, put it into a bacterium to make the corresponding protein and tested its properties.”

Making biocatalytic process less costly

The researchers looked at what reactions the ancestral P450 could catalyse and found that it was very similar to the form of the enzyme found in the human liver responsible for clearing drugs and toxic metabolites. “The key difference is that the ancestral version of this enzyme can work at high temperatures and lasts about a hundred times longer than the modern-day human enzyme (which is already used to some degree in pharmaceutical biocatalysis),” explains Gillam. “This means that it could be used for a longer period in a commercial process and so yield more product for the same amount of enzyme employed, making a biocatalytic process less costly overall.”

And that is not all: the team also showed that its approach works with another enzyme, ketol-acid reductoisomerase or KARI, which can be used for producing biofuels. The strategy might thus be applied to a whole range of enzymes and proteins, says Gillam.

Fundamental studies on proteins will now be easier

As well as potentially revolutionizing commercial biocatalysis, the new thermally stable enzymes will now allow us to more easily study the fundamental nature of proteins, she adds. “Thermostable proteins are much easier to work with because they do not fall apart as quickly as their less-stable counterparts when purified, so we will be able to determine their structure and explore the function of a thermostable ancestor to better understand the related modern (extant) descendant.

“There is much data coming out of genome sequencing projects at the moment but we still don’t have a clue about the structure and function of the proteins many genes encode. This is known as the ‘dark proteome’. Having stable versions of these uncharacterized proteins means we can now study them more easily, work out what they look like and potentially what they do.

“Analysing the structures of these enzymes will also tell us a lot about how proteins have evolved over time. We could possibly exploit these natural evolutionary processes to work out their ‘design rules’ and repurpose proteins for our own ends.”

The researchers say they are now looking at how these thermostable P450s can be used in synthetic biology and plan to design and test novel molecular devices for different applications – such as detecting and cleaning up pollutants in wastewater, to improving the effectiveness and safety of chemotherapy drugs.

“We also want to find out what these ancestral enzymes really did in ancient organisms,” says Gillam. “Were they originally responsible for ‘chemical defence’ as their modern cousins are in humans and other animals? Or did they evolve their catalytic diversity in response to selection pressure during evolution? How were they shaped by evolution into the fascinating and powerful catalysts we have today?”

The present work is detailed in Nature Catalysis 10.1038/s41929-018-0159-5.

Photosynthetic sutures promote wound healing

Sutures with and without microalgae
Fluorescence and scanning electron microscopy images of sutures with and without microalgae loaded. (Courtesy: Acta Biomaterialia 10.1016/j.actbio.2018.09.060 ©2018)

Sutures are extensively used to close wounds. However, rather than promoting active healing of the wound, they act as a passive element that provokes scar formation. In addition, the disruption of blood vessels decreases the presence of oxygen in the wound, limiting the healing. Therefore, there is growing interest in the development of bioactive sutures that promote remodelling of the tissue.

In this context, Tomás Egaña from Pontifical Catholic University of Chile, together with researchers from other South American and European universities, have developed a suture that contains genetically modified microalgae (C.reinhardtii). They showed how these microorganisms in the suture are able to produce oxygen and bioactive molecules such as growth factors, elements that promote wound regeneration (Acta Biomaterialia 10.1016/j.actbio.2018.09.060).

A biofunctional “green” suture

The sutures are loaded with microalgae by simply submerging them in the microorganism suspension at appropriate temperature and illumination conditions, whereby the suture’s filaments absorb the microalgae. In the study, the researchers confirmed that these organisms can proliferate within the sutures and, most importantly, carry out photosynthesis and produce oxygen. Furthermore, they also observed that human skin cells (fibroblasts) seeded on the same well as the suture can metabolize the released oxygen, showing that the seeded microalgae produced enough oxygen to be physiologically relevant.

Oxygen production
Sutures seeded with microalgae for 14 days are able to produce oxygen (bubbles) in vitro. (Courtesy: Acta Biomaterialia 10.1016/j.actbio.2018.09.060 ©2018)

To further increase the potential of this technology, the researchers investigated the possibility of the microalgae producing functional molecules that promote healing, such as growth factors. To do so, they genetically modified the microalgae to produce such factors (VEGF, PDGF and SDF-1α). For this, the investigators introduced the DNA sequences of these growth factors into the microalgae genome. They then seeded the microalgae in the sutures and observed how they produced these factors with a sustained release for 14 days. The growth factors also had biological activity on human cells in vitro.

Finally, the researchers proved that the sutures preserved their mechanical properties after hosting the microalgae for 14 days. In addition, after suturing skin for 45 times with the suture and cryopreserving (freezing at -80 °C) it, the microalgae maintained their viability and growing capacity. This demonstrates the feasibility for their repeated use and preservation.

What is next?

This technology represents a novel approach and an important advance in the development of biofunctional sutures. Also, it can be applied to other biomaterials. However, many questions remain unanswered: How feasible is the sterilization of the sutures? How do we eliminate the microorganisms once the patient is treated? How can we supply light to these photosynthetic materials? The answers to these questions and other challenges will be the focus of future efforts of Egaña and his research team.

Doubled raw materials use is climate risk

Just when you might think the world has heard an unmistakable warning of the need to curb climate change drastically and fast, along comes another warning, about humans’ voracious appetite for the raw materials we use so profligately.

Its message is simple: one of the main causes of the Earth’s growing warmth is likely to be twice as severe 40 years from now as it is today.

This latest warning, from the club of the world’s richest countries, the Organisation for Economic Co-operation and Development (OECD), says consumption of raw materials is on course to nearly double by 2060 as the global economy expands and living standards rise.

And that will mean a steep increase in emissions of the greenhouse gases which drive global warming. Total emissions are projected to reach 75 gigatonnes (Gt) of carbon dioxide equivalent (CO2-eq.) by 2060, of which materials management would constitute about 50 Gt CO2-eq. A gigatonne is a thousand million tonnes. Gt CO2eq is an abbreviation for “gigatonnes of equivalent carbon dioxide”, a unit based on the global warming potential of different gases.

If you find it hard to visualise raw material, the OECD offers some helpful examples. The main sort of “stuff” it’s talking about includes the building blocks of the modern world: sand, gravel and crushed rock. Metals are next, and third is coal. It uses a disarmingly wide image to bring the message home: “The total raw materials consumed by an average family in a day would fill up a bathtub”.

The full OECD report, the Global Material Resources Outlook to 2060, will be available from 27 November, but a preview  was released this week at the World Circular Economy Forum in Yokohama, Japan.

The Outlook expects global materials use to rise from 90 gigatonnes (GT) today to 167 GT in 2060, because of the increase in world population to 10 billion people expected by then, and the rise in average global income per capita to converge with the current OECD level of US$40,000 (€34,900).

Immense human footprint

The projected figures are immense. But so are those that quantify today’s hunger for materials. Scientists calculate, for instance, that the weight of objects made by humans is about 30 trillion tonnes, and that by 2050 we shall have built another 25 million km of roads, enough to circle the Earth 600 times. None of this bodes well for us, let alone for the other species that share the planet.

Without action to address these challenges, the projected increase in the extraction and processing of raw materials such as biomass, fossil fuels, metals and non-metallic minerals is likely to worsen the pollution of air, water and soils, and contribute significantly to climate change, the OECD says.

This increase will happen despite both a shift from manufacturing to service industries and continual improvements in manufacturing efficiency, which has lessened the amount of resources consumed for each unit of GDP.

Without this, it says, environmental pressures would be even worse. The projection also acknowledges flattening demand in China and other emerging economies as their infrastructure booms end.

Coal boom

The preview report says the biggest rises in resource consumption will be in minerals, including construction materials and metals, particularly in fast-growing developing economies. The OECD projects a big increase in coal consumption by 2060, but a much smaller increase for oil.

Its overall conclusion on the impact of materials use on climate change is bleak: “More than half of all greenhouse gas (GHG) emissions are related to materials management activities. GHG emissions related to materials management will rise to approximately 50 Gt CO2-equivalent by 2060.”

The report’s global environmental impact analysis of the extraction and production of seven metals (iron, aluminium, copper, zinc, lead, nickel and manganese) plus building materials − concrete, sand and gravel − also shows significant impacts in areas like acidification, air and water pollution, energy demand, human health and the toxicity of water and land.

Journal editors share their views on the future of open-access publishing

This week marks Open Access Week 2018, which has as its theme “designing equitable foundations for open knowledge”. Now in its 10th year, the global event aims to promote the benefits of open-access publishing. 

To mark the week, Physics World has talked to editorial board members of IOP Publishing’s open-access journals to get their views on open access and its future. From the comments below, it seems that open access is becoming more popular in many areas of research. Yet challenges remain, particularly when it comes to cost and having the funds available in grants to pay for open-access publication.

How much demand for open-access publishing do you see in your research community and how is that changing? Do you see any notable regional differences?

Barry Sanders (BS), University of Calgary, Canada – editor-in-chief of New Journal of Physics

Green open access, which involves placing the paper behind an embargo, typically for 12 months, is widely used by the quantum-information community and has been ubiquitous for many years. Gold open access, in which the paper is made immediately available to read upon payment of an article processing charge (APC), is also popular in the community. Indeed, quantum information has been one of the strengths of New Journal of Physics – a gold open-access journal.

Sarbajit Banerjee (SB), Texas A&M University, US – senior advisory panel member on Journal of Physics Communication

Demand for open-access publishing is certainly increasing, with the biggest driving force being mandates from funding agencies – particularly for colleagues in Europe. Yet conflicts between perceived prestige and rigour on the one hand and open-access dissemination on the other hand, remain to be adequately resolved. Early-career researchers also face increasing institutional and cultural pressures to publish in high-impact-factor journals. The Venn diagram of overlap between high impact factor and open access is not substantial, albeit, encouragingly, it is not entirely null.

Eugenie Hunsicker (EH), Loughborough University, UK – senior advisory panel member on Journal of Physics Communication

Open-access publishing has huge benefits in terms of broadening access to new quality-controlled science papers. This has particular implications for scientists working in countries in which there is no extensive access to journals. The UK is currently putting more money than ever into developing research potential in these countries. Open access is critical for ensuring these efforts can flourish.

Open access is now a very exclusive club dominated by a few developed countries. The imbalance is worrisome

Arturo Sanchez-Azofeifa

Wilfried Winiwarter (WW), International Institute for Applied Systems Analysis, Austria – senior advisory panel member on Environmental Research Communications

There is a strong trend in environmental sciences towards open access. With public money typically funding this kind of research, funding bodies such as the European Union – via its Horizon 2020 programme – require that results are openly accessible. Many national funding bodies have also followed suit. Scientists are willing to adopt open-access practices if there is dedicated accessible funding available for open-access charges or project funding is sufficient to allow for open access. The current trend for open access has certainly been triggered by the availability of funds that allow the option of publishing in hybrid journals. With the increasing number of open-access publications, such funding has started to dwindle, so it is expected that the trend may reverse – unless research institutions themselves also adopt open-access policies, for which no general directions are currently visible.

Arturo Sanchez-Azofeifa (AS), University of Alberta, Canada – senior advisory panel member on Environmental Research Communications

There is a huge demand for open access in developing countries that have limited access to good scientific papers. As funding agencies start to request access to more open-source publications, it is not a matter of how, but when we will have 100% open access. Although some journals have discounts to publish open access, the costs can be extremely expensive. In my opinion open access is now a very exclusive club dominated by a few developed countries. The imbalance is worrisome.

Paul Palmer (PP), University of Edinburgh, UK – senior advisory panel member on Environmental Research Communications

There is already a massive appetite for open-access publishing in my research community. Many of the relatively new European-led journals already use a publishing model that includes the open-access publication of a “discussion” paper and the final paper. Although this model is not perfect by any means, the review process is more transparent than traditional publishing models that are used by some US journals. However, the situation in the US is beginning to change.

Dan Rubenstein (DR), Princeton University, US – reviews editor of Environmental Research Letters

Ease of access to a wide readership is advantageous given that funding agencies are supported by the tax payer and scientists want to reach colleagues all over the world. Open-access publishing helps facilitate this.

Daniel Kammen (DK), University of California, Berkeley, US – editor-in-chief of Environmental Research Letters

Demand for open access is very high and I am seeing requests from everywhere – hence the need for open access.

Thomas Anthopoulos (TA), King Abdullah University of Science and Technology, Saudi Arabia – senior advisory panel member of JPhys Materials

The volume of open-access papers seems to increase with time. I believe that in some countries the open-access route is dictated primarily by funding sources, rather than by the authors themselves.

What are the benefits of open-access publishing for researchers in your community?

BS: Researchers in quantum information appreciate the easy accessibility of gold open access for readers and the versatility that it offers as an online only service.

SB: The benefits are higher visibility of publications and the ability for researchers worldwide to easily access them. In disciplines with a more translational or applied emphasis, open access makes research accessible to industrial practitioners and thereby has the potential for greater impact. I think the emphasis on citations alone is misguided as a metric for evaluating such research.

Providing free access to research is a no brainer

Paul Palmer

WW: One of the biggest advantages of open access is that research can be easily distributed and accessed, which has proven to lead to higher citation rates. Also, copyright worries and posting of articles on websites are simplified. Scientists are normally not interested in legal issues – they want to access high-quality scientific literature and they wish their own research can be recognized as high quality by as large as possible a scientific community.

AS: When you make your papers open access you can open it up to a broad community and also make an impact via social media and other sources to promote your research. We are now asked to indicate in our grant applications how our research makes a difference; open access helps to answer that question.

PP: Open-access publishing allows everyone to access the latest research, which is often funded through public money. Providing free access to research is a no brainer. Open-access publishing generally improves the dissemination of information – not only for researchers in developing countries who may not have access to subscription-based journals, but also for teachers in schools so that they can more easily incorporate new findings into their lessons.

DR: Scientists want exposure to as many readers as possible, especially those in developing countries who do not have libraries paying the subscription costs for many of the major journals.

TA: Open-access publishing is welcomed especially by scientists in universities and countries with limited resources or at places where research is not a priority.

EH: Open access also has implications for scientists who have a break in their formal employment in science. This can cut off researchers from access to current research. Open access allows these individuals to keep on top of developments in their field and enable them to re-enter the scientific workforce again at a later point.

How do researchers in your community feel about funder mandates for open-access publication?

BS: Researchers in quantum information generally appreciate the importance of open access, especially now that quantum information is increasingly important to industry, investors and the public who face a paywall if the article is only available through subscription journals. On the other hand, many researchers feel trepidation that precious funding could diminish through paying APCs to publish research.

SB: I think researchers broadly are sympathetic to funder mandates and their intentions, but there is some wariness about “unfunded mandates” and whether APCs associated with open access become a barrier to entry.

WW: Such mandates are being recognized and are welcomed as long as there are no funding conflicts. Publishing costs remain quite low in the overall budget of a scientific project, but they have been increasing and cost is one criterion for selecting among high-quality journals. Researchers do have some liberty to allocate scientific articles to certain projects, but limitations in funding possibly takes some articles from being open access.

AS: I believe that people in our community do not have a problem with mandates. The problem is to have a mandate and not provide the dollars to fulfil it.

Publishing all of my work  in open-access journals seems impossible, primarily due to limited funding

Thomas Anthopoulos

PP: A funder that mandates open access is happy to pay for it now but I suspect they are already questioning why some journals still have a two-tier system, with additional charges associated with an open-access option. I think the onus is on journals to change and with one or two notable exceptions most journals are beginning to dissolve the two-tier publication system.

DR: If scientists have grants they can often budget for the publication charge. If not, then open-access journals are off-limits.

DK: The main concern is the cost for people who have no budget for it in grants, which is very few.

TA: Publishing all my work in open-access journals seems impossible, primarily due to limited funding. However, this is changing at least in some countries around the world. So, one of the challenges we are currently facing is to balance traditional publication routes with open access.

EH: Open access can mean many different things. While in general the community is supportive of increasing access to publications, there is concern about the costs associated with publishing in certain types of open-access outlets. For some authors, this can be an insurmountable barrier to top-level publishing. There is also concern about the loss of revenues for professional societies, which have traditionally relied on journals for a large proportion of their charitable budget. Thus, there is concern that grants and activities will need to be cut if new policies drastically reduce this income.

What is the greatest challenge in ensuring open access is more equitable, accessible and fair?

BS: The greatest challenge is making open access affordable for all authors, especially in developing countries.

SB: We still need better models for APCs that are paid institutionally or by funders so that it does not become a barrier to entry. Open access must maintain standards for peer review and not be viewed as a watered-down version of rigorous science.

WW: The research landscape in general is not equitable, accessible or fair. National and cultural priorities make and create differences. General accessibility of open-access publications reduces such differences but open-access costs can again increase it. Allowing for waivers of such charges enhances equitability. If waivers are in place on a country-by-country basis, research programmes and activities that involve research in developing countries may also take advantage of joint open-access publications, such as in special issues.

AS: There are two important challenges. The first is funding to support open access. This should not come out of current allocations. A funding agency should not provide the same level of funding as before and add the expectation that papers will be open access. The second challenge is the democratization of research. We need to try to allow developing countries to publish in good open-access journals. It is nice to have journals that are open access if they remain controlled by researchers with associated funding from developed countries it will make little difference. An effort to bring scientists from developing countries into the open-access realm is fundamental and necessary.

PP: I think the greatest challenge for publishers is to justify their continued existence. As the global scientific community grows, so does its output. At the same time, scientists want their information to be shared quicker so repositories like arXiv continue to grow in importance. The primary role for a journal is to maintain a reputation for quality research using rigorous peer review but in some cases this reputation is already being eroded, perhaps overwhelmed, by the volume of papers being submitted.

DR: Costs. Someone has to pay for publication but somehow an egalitarian model has to be created where those who can, pay, and those who cannot need to be subsidized. But in today’s online world, the cost of publishing work should be lower than in the past. Until the costs are reduced, most scientists will go where they do not have to pay, or at least do not have to pay as much. Grants are always smaller than desired and money for publishing has the lowest priority.

Feynman’s ratchet is built at last using 19 optical tweezers

A thought experiment proposed more than 50 years ago by Richard Feynman has finally been realized in the lab by physicists in the US and China. “Feynman’s ratchet” is a microscopic heat engine that converts thermal fluctuations into work when connected to two heat sources at different temperatures. Although the device has a very low efficiency, its creators believe it could have a number of applications, such as providing a better understanding of molecular motors that drive living cells.

Feynman’s thought experiment is a way of showing how the second law of thermodynamics cannot be violated. He envisaged a tiny set of vanes attached to the end of a shaft that are bombarded by gas molecules in a box. The other end of the shaft is attached to a ratchet, so the wheel can only turn in one direction.

The idea is that the molecules in the gas strike the vanes from random directions due to their Brownian thermal motion. But because the shaft is also connected to the ratchet, only motion forcing the vanes to turn in one direction would result in the rotation of the shaft. The upshot would be directed motion – which could be harnessed to do work – generated from random thermal movements.

Jumping pawl

However, Feynman explained that the internal workings of the ratchet would prevent such directed motion from taking place. In a ratchet (see figure), a gear wheel with asymmetrical teeth can only turn in one direction because a spring-loaded “pawl” next to the wheel allows the more gently-sloping side of each tooth to run past the pawl – but blocks the steeper side when rotation is in the opposite direction. Feynman pointed out that if a ratchet could be made small enough to be turned by molecular collisions, the friction needed to prevent the pawl bouncing clear of the ratchet as it drops down from one tooth to the next would create enough heat to agitate molecules within the device and cause the pawl to jump up and allow the wheel to turn the wrong way. As with macroscopic heat engines, he concluded, there would have to be a temperature difference for the device to work – either the gas would have to be hotter than the pawl, or vice-versa.

Until now no-one has built such a tiny ratchet because of significant technical challenges that include how to prevent convection from washing out thermal fluctuations. But now Tongcang Li of Purdue University in the US and colleagues have succeeded using a 780 nm-diameter ball of silicon dioxide confined to a 1D optical trap set up inside a small tank of water.

The trap is created by combining 19 optical tweezers in one of two ways. Either the tweezers are overlapped to form a smooth, constant potential that leaves the ball free to move in either direction along the trap’s axis as it is knocked about by water molecules – in other words, the virtual ratchet and pawl are disengaged. Or the tweezers combine to create a saw-tooth potential, constraining the ball to move in one direction only – in which case ratchet and pawl are engaged.

Temperature difference

While the temperature of the gas is represented by the temperature of the water, the temperature of the pawl – the second heat reservoir – instead has a more abstract expression: the frequency with which the trap switches between saw-tooth and smooth potentials. The idea is that when the pawl is hotter it is more likely to jump up and allow the ratchet to turn the wrong way.

As Feynman predicted, when the two heat baths have the same temperature the ball is sometimes bounced slightly to the left and other times slightly to the right, but there is no net motion. But when they change the switching rate between the virtual ratchet’s two different states – so raising the temperature of one bath over the other – they find that the ball migrates along the trap. In other words, the ratchet undergoes a net rotation in one direction, which, they showed – by adding a slope to the flat potential – allows the system to perform work.

Feynman was wrong

The researchers also showed that Feynman got quite an important detail wrong. Feynman thought the ratchet could operate as efficiently as a Carnot engine, while other physicists have argued that is impossible because the device requires contact with two heat sources at the same time. In fact, Li and co-workers measured an efficiency of less than 1% – in contrast with the 90% theoretically possible for a Carnot engine operating between the temperatures in question.

Li says that the low efficiency is “a little bit disappointing” but insists that their device provides “an important platform to study microscopic heat engines”. He reckons it could shed light on the mechanisms underlying molecular motors, which, he says, involve Brownian motion and “are closer to Feynman’s ratchet than a Carnot engine”.

Ignacio Martínez of the Universidad Complutense de Madrid praises the team for its “beautiful study” in fundamental physics. He argues that the “kinetic” temperature and virtual pawl-ratchet system render the demonstration an “experimental simulation”, rather than a real engine. However, he believes the work could help develop technology that exploits fluctuations even on larger scales, such as charging small electronic devices using ambient electromagnetic waves. “These fundamental studies are a pivotal part of future applications,” he says.

The research is described in New Journal of Physics.

The science of climbing Mount Everest

In this episode of Physics World Weekly, we have a special extended interview with Melanie Windridge, a physicist with a taste for adventure. Earlier this year, Windridge achieved the personal feat of trekking to the highest point on Earth – the summit of Mount Everest. She speaks to Physics World’s James Dacey about how science and technology have made the ascent more accessible since the original ascents of the 1950s.

Windridge also wrote about the experience in the September issue of Physics World and produced a series of videos about the Science of Everest for the Institute of Physics (which publishes Physics World).

At the end of the podcast, Dacey is joined by Physics World’s general physics editor Hamish Johnston. They discuss how a new measurement of the electron’s electric dipole moment (EDM) has cast doubt on several prominent theories of physics beyond the Standard Model of particle physics.

If you enjoy what you hear, then you can subscribe via the Apple podcast app or your chosen podcast host.

Neutrinos shine new light on fusion reactions in the Sun

Neutrino fluxes generated by nuclear reactions inside the Sun have been measured more precisely than ever before. Using a detector housed under the Gran Sasso mountain in central Italy, the Borexino collaboration has captured neutrinos from four different reactions involved in the creation of helium-4 from hydrogen. The results confirm the nuclear origin of solar power and could help to pin down the abundance of elements heavier than helium inside the Sun.

Some 99% of the Sun’s energy is generated through reactions that begin with the fusion of two protons. This “proton-proton chain” proceeds via a number of different routes. The most common route involves the fusion of two helium-3 nuclei, while others feature the temporary production of beryllium-7 and one the creation of boron-8. Occasionally, the chain can also start with the fusion of two protons and an electron (pep).

To detect the neutrinos created in each of these reactions, Borexino employs a 300 ton sphere of hydrocarbon liquid scintillator. Any neutrino scattering off an electron inside the scintillator generates a flash of light that is picked up by an array of photomultiplier tubes. Crucially, the experiment has extremely low levels of radioactive interference, thanks both to the 1400 m of rock above the Gran Sasso National Laboratory – which blocks incoming cosmic rays – and to the ultra-pure materials used to contain and shield the detector.

Lowest uncertainties

Using data collected between 2012-16, the international collaboration reports values for the fluxes of neutrinos generated from: the initial fusion of two protons; the capture of an electron by beryllium-7; the beta decay of boron-8; and pep fusion. As pointed out by collaboration spokesman Marco Pallavicini of the University of Genoa, Borexino has already measured each of these quantities before, and indeed the boron-8 flux has been pinned down more precisely by detectors employing large tanks of water – the Sudbury Neutrino Observatory (SNO) in Canada and Super-Kamiokande in Japan. The novelty, he says, is to have measured all four quantities with the same set of data and to have done so with the lowest uncertainties yet for the proton-proton, beryllium-7 and pep reactions – 9.5%, 2.7% and 15% respectively.

It is an impressive suite of measurements

Gabriel Orebi Gann

Gabriel Orebi Gann of the University of California, Berkeley, who works on SNO and other neutrino experiments, praises the research. She says that the latest results underline Borexino’s reputation for furthering our understanding of both the Sun and neutrinos themselves. “It is an impressive suite of measurements,” she says.

Metallicity puzzle

Aldo Serenelli of the Institute of Space Sciences in Barcelona points out that the new results yield a solar luminosity – derived from the total power generated by nuclear reactions in the Sun – that is within 10% of the measured value. He also says that the new data “contribute marginally” to solving the “metallicity puzzle” – in other words, establishing just how abundant heavier elements such as carbon, nitrogen and oxygen are in the Sun. The Borexino results, he explains, point to a slightly higher core temperature that would tend to favour relatively high abundances but cautions that the higher temperature can be explained in other ways.

The new data are also relevant to fundamental physics. The collaboration has determined the survival probability of solar electron neutrinos at different energies, thereby, it says, “probing simultaneously and with high precision the neutrino flavour conversion paradigm, both in vacuum and in matter-dominated regimes”.

In future, Serenelli argues there is a chance that Borexino could measure neutrinos from the carbon–nitrogen–oxygen (CNO) cycle. An alternative to the proton-proton chain that uses carbon and nitrogen nuclei to catalyse the conversion of hydrogen into helium, CNO is thought to provide most of the energy for more massive stars. And although it would only generate about 1% of the Sun’s output, observation of the associated neutrinos should settle the metallicity puzzle, says Serenelli, because the flux would be very sensitive to the presence of heavier elements in the solar atmosphere.

Thermal coat

Borexino’s chance of bagging such neutrinos was boosted in 2016 after the collaboration surrounded the detector with a thermal coat. Previously, temperature changes within the lab had set up convection currents in the scintillator that would transport radioactive impurities from the nylon vessel surrounding the liquid into the core of the detector. But now, according to Serenelli, the collaboration is in a better position to monitor the relevant background (from bismuth-210) and so potentially measure CNO neutrinos. “There are high expectations they will succeed,” he says.

To maximize the odds of success, Pallavicini says that he and his colleagues would ideally like to further raise the purity of the liquid scintillator. But that option is complicated by the fact that the experiment may have to shut down for good by 2020 to comply with an environmental law concerning groundwater.

However, Borexino is not the only experiment potentially capable of detecting CNO neutrinos. One is SNO+, a revamped version of SNO – due to start taking data in 3-4 months’ time – that will contain liquid scintillator rather than heavy water and which Orebi Gann notes will be larger and deeper than Borexino. “The primary goal of SNO+ is a search for neutrinoless double beta decay,” she says. “But if radioactive backgrounds are low enough then SNO+ could have sensitivity to the CNO cycle”.

The research is described in Nature.

Nanoparticle-coated membrane improves dental implants

Uncoated and coated membrane
SEM images of uncoated (top) and nanoparticle-coated (bottom) collagen membrane. Confocal imaging shows that cells seeded on either membrane are morphologically comparable.

Dental implants are commonly used to replace missing teeth. The success of such an implant relies on solid anchorage into the alveolar bone that contains the tooth sockets. But many patients do not have sufficient bone volume to secure the implant and require bone reconstruction before tooth implantation.

The reconstruction procedure involves infilling a bone substitute into the alveolar socket to initiate bone formation. Infection, however, remains a major concern in dental surgery. A barrier membrane can help prevent infection, while also blocking soft-tissue ingrowth as the new bone forms. Now, a research team headed up at the University of Western Australia has fabricated a silver nanoparticle (AgNP)-coated collagen membrane, exploiting the natural anti-bacterial properties of silver to prevent infection (Biomed. Mater. 10.1088/1748-605X/aae15b).

Silver coating

The researchers used CelGro collagen membrane, which is approved for dental guided bone regeneration, and coated it with AgNPs using two low-temperature fabrication methods: sonication and sputtering. Images of the coated membranes showed that the AgNPs were evenly coated on both sides using sonication, but on only one side using sputtering.

Scanning electron microscopy revealed that sonication could accurately deposit AgNPs on the membrane, with higher AgNP concentrations depositing more nanoparticles on collagen fibres. Sputtering, however, was difficult to control and led to large uneven deposition of AgNPs.

To test the membrane’s anti-bacterial properties, the researchers prepared AgNP-coated collagen membranes with different nanoparticle concentrations and placed them on bacterial inoculation plates. After four days, samples fabricated via either sonication or sputtering exhibited excellent anti-bacterial effect against two common strains of bacteria, with maximum effect achieved at a concentration of 1.0 mg/ml.

Anti-bacterial effect
Anti-bacterial effect of the AgNP-coated collagen membrane on S. aureus and P. aeruginosa bacteria.

Next, the team seeded mesenchymal stem cells (which can differentiate into a variety of cell types, including bone cells) on AgNP-coated collagen membranes. After 24 hr in culture, they saw a AgNP-dose dependent decline in cell numbers on sonication-coated samples; however, proliferation rates after day 1 were similar. They note that sputter-coated collagen severely inhibited cell growth — suggesting that this technique is not suitable for coating collagen membranes for cell proliferation.

The researchers also assessed the cell membrane integrity using an LDH leakage assay. After 24 hr, they saw an increase in the amount of leaked LDH, correlating to the concentration of AgNP on the membrane. They noted a significant increase between the 1.0 and 1.2 mg/ml sonication groups, indicating that AgNPs can damage the cell membrane.

To maximize antibacterial effectiveness while minimizing cytotoxicity, the team chose 1.0 mg/ml AgNP as the optimal coating concentration. At this dose, confocal imaging showed that cells seeded on AgNP-coated collagen membrane were morphologically comparable to cells on uncoated membranes.

Anti-inflammatory capacity

Inflammation during bone reconstruction can result in a less reliable preparation for the tooth implant. To assess the anti-inflammatory effects of AgNP coating, the researchers examined the expression of two inflammatory cytokines, IL-6 and TNF-a, in macrophages seeded on collagen membranes.

When the cells were stimulated to initiate inflammation, IL-6 expression was lower on AgNP-coated than on uncoated membranes, 1 and 2 hr after stimulation; TNF-alpha expression was only suppressed 1 hr after. Released IL-6 and TNF-alpha were further suppressed 2, 4 and 8 hr after stimulation. These findings demonstrate the anti-inflammatory properties of the coated membranes.

Finally, the researchers examined the osteogenic differentiation of mesenchymal stem cells seeded on AgNP-coated collagen membranes. Expression of early osteogenic markers was far higher in cells cultured on AgNP-coated membranes than on uncoated membranes at days 3 and 6. However, there was no significant difference when cells continued to be cultured to day 9.

Osteogenic markers expression
Cell differentiation on AgNP-coated collagen membrane. Expression of osteogenic markers (RUNX2, ALP and OPN) was significantly increased after 3 and 6 days culture in the AgNP-coated group.

The authors conclude that the optimized AgNP-coated collagen membrane showed the ability to guide bone regeneration, as well as exhibiting anti-bacterial and anti-inflammatory capacity, with limited cellular toxicity. They emphasize the potential application of such membranes in dental surgery, particularly for alveolar bone augmentation and bone graft integration.

International physics hub opens African outpost

The International Centre for Theoretical Physics (ICTP) in Trieste, Italy, has officially opened its first outpost in Africa. At a ceremony held on 18 October at the University of Rwanda in Kigali, the ICTP-East African Institute for Fundamental Research (ICTP-EAIFR) will aim to raise the quality of science research and education in Africa. It is the third ICTP outpost following institutes in Brazil and Mexico.

The ICTP-EAIFR will focus on research and teaching in high-energy physics, geophysics and condensed-matter physics. The Rwandan government is funding the centre with an estimated budget of $6.5m over the first five years. The ICTP, in collaboration with the University of Rwanda, will provide support in terms of books, personnel and equipment.

“We believe that by developing a critical mass of African scientists and physicists we can work together and make Africa great,’’ says ICTP director and theoretical particle physicist Fernando Quevedo.

The centre is of immense value to the continent to invest in our own human capital and training people in fundamental research

Amanda Weltman

The first intake of 16 students – including nine from Rwanda — have already been selected and the centre will train students through short courses and workshops. ICTP-EAIFR’s interim director Omololu Akin-Ojo told Physics World that the MSc and PhD programmes will match the quality offered by the main institute in Italy. “EAIFR will continue to carry out research and make discoveries for African development and advancement,” he says.

According to Akin-Ojo, Rwanda was selected to host the centre due to the country’s support of science, how easy it is to set up new centres there and the “high level of transparency” in the country. He adds that the centre does not yet have funds for bursaries and scholarships for students, but that they are seeking support “from different sources”.

Making improvements

Theoretical physicist Amanda Weltman from the University of Cape Town says that the ICTP has “immense experience and successful working relationships around the developing world” and that the new centre will foster a range of improvements in Africa from scientific breakthroughs to technological advancements and improving science policy. “The centre is of immense value to the continent to invest in our own human capital and training people in fundamental research,” she adds. 

The ICTP-EAIFR is the ICTP’s third foreign-based institute after it opened the South American Institute for Fundamental Research in Sao Paulo, Brazil, in 2012 followed a year later by the Mesoamerican Centre for Theoretical Physics at the Autonomous University of Chiapas in Mexico. The ICTP plans to open its first outpost in Asia — the ICTP-Asia Pacific — in Beijing, China, in November.

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