The performance of boys and girls in school is much more similar in science, technology, engineering and mathematics (STEM) subjects than in other disciplines. That is according to an analysis carried out by researchers in Australia of the grades of over 1.6 million students around the world. The authors say that their study disproves the “variability hypothesis”, which suggests that male over-representation in STEM careers comes from a greater variability in grades among boys than girls (Nature Communications9 3777).
Led by biology PhD student Rose O’Dea from the University of New South Wales, the researchers examined 227 studies of student grades that were carried out between 1931 and 2013. They looked at the variability – defined as the width of the distribution curve – of exam results between girls and boys and found that the biggest differences were in non-STEM subjects. Here they found that the mean grades of girls were 7.8% higher than boys and 13.3% less variable. In STEM subjects, however, these figures were roughly halved: girls grades were 3.1% higher and 7.6% less variable than boys.
People in general seem to continue to believe that the gender gap’s origins are biological, rather than the effect of compounding stereotypes
Lara Perez-Felkner
By analysing the grade distributions, the researchers found that the top 10% of grades in STEM subjects had an equal gender ratio, while non-STEM subjects were female-heavy. “Our results support greater male variability in academic performance, but they don’t support gender differences in variability as an explanation for gender differences in workforce participation because we find the smallest gender differences in variability in maths and science,” O’Dea told Physics World.
Top of the class
The authors say their work disproves the variability hypothesis, which is often – mistakenly as it turns out – said to be the reason why boys outnumber girls at the top of the class, despite girls achieving higher average grades. “Greater male variability was first written about in the 1800s as an explanation for why the geniuses and fools in society were men,” says O’Dea. “Since then women have had greater access to higher education and girls are now out-performing boys at school on average, but women are still under-represented in maths-intensive fields. The variability hypothesis is now used to explain this discrepancy.”
O’Dea adds that the study highlights gender differences in humanities as one possible reason why fewer females opt for STEM careers. In STEM, girls face more male competition, she says, along with negative gender stereotypes and the challenges of trying to succeed in male-dominated workplaces. This means, she thinks, that STEM can be a riskier option for girls compared to boys. “There is also some evidence from other studies that students who are good all-rounders – who get high marks in both language and maths – are less likely to stick with STEM, regardless of their gender,” says O’Dea, adding that working on increasing boys’ language skills could be another way to reduce the STEM gender gap because this is the area with the biggest gender differences.
“Despite its limitations, scientists and people in general seem to continue to believe that the gender gap’s origins are biological, rather than the effect of compounding stereotypes and signals young people get towards and away from STEM careers depending on their gender identity,” Lara Perez-Felkner, a sociologist at Florida State University in the US told Physics World. “While this study does not singularly disprove [the variability] hypothesis, it sheds further doubt on its significance. If mathematical ability variation is so important, we would see no variation across nations. Biology should look the same everywhere. Rather, we see a considerable amount of variation by country.”
The European Commission has signalled that it is considering a “net zero” emissions goal and, in the UK, the Labour Party now has that as a key policy – net zero by 2050 rather than the current 80% emissions cut target by 2050. What does net zero mean, and is it possible? The first part is easy. Net zero means that carbon dioxide and other greenhouse gas emissions are reduced 100%, to zero, although some can be allowed if compensatory carbon negative processes are introduced, for example, air capture of carbon dioxide.
How to achieve this is a bit more complex. The most obvious approach is not to produce any more carbon dioxide. In the energy sector that means using non-fossil energy sources, i.e. nuclear or renewables. However, neither is entirely carbon-free – at present we use fossil fuel to make the materials for the energy conversion technologies involved and, in the case of nuclear, to extract and process nuclear fuel. Nevertheless, they are both low-carbon options.
In its new Green Transformation pamphlet, the Labour Party says it will use both nuclear and renewables to “ensure that 60% of the UK’s energy comes from low-carbon or renewable sources within 12 years of coming to power”, i.e. by 2030 if that event happens soon. The inclusion of some new nuclear is controversial but together, renewables and nuclear would supply 85% of UK electricity, up from 50% now (30% renewables, 20% nuclear). However, renewables would no doubt continue to dominate the mix and presumably then be ramped up further to get to near 100% of supply by 2050.
Europe will need to compensate for some of its emissions by going net-negative after 2050
European Climate Foundation
To make this viable with variable renewables, Labour says it will “upgrade and invest in flexible energy networks capable of supporting a transition to decentralised renewable energy, by bringing the UK’s energy transmission and distribution networks back into public ownership”. This, it says, means “making more use of local, micro grids and of batteries to store and balance fluctuating renewable energy, and providing the necessary investment to connect renewable energy sources to the grid”.
The plan would involve a sevenfold increase in offshore wind-farms (to 52 GW), a tripling of solar power (to 35 GW) and doubling of onshore wind farms (to 30 GW) by 2030. That would go a long way to meeting the 60% energy target. However, although energy for transport is excluded in the 60% target, it does include heat, and for that the plan is to provide 44% of heat from renewable sources by 2030 and reduce heat demand from buildings by 23%. For example, Labour wants to reinstate the Zero Carbon Home programme.
Zero appearance
Even so, there would still be some way to go to net zero — 100% zero carbon across the board. What would that actually look like? Some idea comes from a new study by the European Climate Foundation (ECF) of EU pathways to zero emissions. It says that “commercially available solutions can already take us about 75% of the way to net-zero if deployed at scale. The remaining 25% can be achieved based on known approaches and technologies for which further scaling up and commercialization is needed”.
The report looks well beyond energy supply technology and says that, to get to net zero, “we need to widen the range of options being used, including by putting more focus on how we operate as a society. Innovation in our consumption patterns and increasing potential natural carbon sinks need to be combined with the more typical technical options such as energy efficiency, fuel shift, zero-carbon power production and electrification.”
So the ECF offers three possible 2050 scenarios. The “Shared efforts” scenario assumes a comparable level of effort is maintained across all sectors and “levers”, i.e. there is no emphasis on any specific carbon mitigation option. The “Technology” scenario emphasizes efficiency and innovative technological options by raising their ambition to the highest levels, e.g. energy efficiency, electrification, hydrogen, and carbon capture and storage. It leads to a 41% energy demand cut by 2050. The “Demand-focus” scenario uses demand-side levers to reduce the overall demand further, e.g. for energy (with a target of -64% by 2050), as well as for products, including meat, which implies that technological levers can be reduced compared to the Shared efforts scenario.
The ECF says it won’t be easy to make some of these changes, but suggests that most of the gains will come from efficiency and energy use changes, not from renewables or other supply-side changes. It also says “negative emission” options (like BECCS, Biomass with CCS) will only make up a small part, though land-use changes may provide a bit more.
Nevertheless, the report stresses “the importance of deploying all mitigation actions possible including land-use sinks and other options for removal of GHG [greenhouse gases] from the atmosphere”, and notes that “in our three scenarios, improved land-use practices could support around 600 megatonnes of CO2 equivalent per year of GHG sinks, which amounts to about 10% of 1990 emissions and can help us reach net-zero by 2050”. However, that’s still quite small and it notes “other options to remove GHG from the atmosphere (e.g. biomass use combined with CCS) have significant limitations as well”.
Overall then, “the European carbon emissions budget is very tight and reaching net-zero by 2050 is unlikely to be sufficient” to reduce cumulative emissions longer term, and so it concludes that “Europe will need to compensate for some of its emissions by going net-negative after 2050”. This means that, since they will be needed later on, in the short term the “limited natural sinks and other carbon dioxide removal (CDR) options will not be an alternative for the emitting sectors. Each sector needs to reach close to zero emissions around mid-century or shortly after.”
That may all sound quite onerous and likely to be expensive, and as I have noted in earlier posts, not everyone thinks that large-scale negative emission options like BECCS will be needed or viable. However, big changes will be needed, although the cost pattern for each scenario differs. Crucially, the ECF report says that all the scenarios cost less than the business-as-usual scenario — cutting carbon saves money.
Plan check
So how does Labour’s plan stack up against these major requirements for rapid change? Its energy supply proposals are ambitious, but with costs falling rapidly, the UK should be able to go well beyond the 63 GW of renewables suggested as possible by 2030 in the most recent UK government projections. Though the 117 GW total that Labour proposes may be stretching it, and would surely not all be needed by 2030 — energy demand is actually falling. At present, the UK has around 40 GW of renewables, delivering around 30% of its electricity, so very roughly 80 GW might deliver 60% of electricity. However, there could also be a need for some extra electricity for heating, depending on how this is done. So maybe 100 GW or more might be required in all, if the aim is to get 44% of heat demand met from renewables — although not all of that would have to be met via electricity-generating renewables.
As noted above, provocatively, Labour’s 60% target also includes the use of nuclear power, which is arguably only retained due to the political strength of the nuclear lobby. With costs rising and demand falling, it seems an odd choice. There are plenty of non-nuclear scenarios around, with renewables expanding to supply all energy needed in the power, heat and road transport sectors. What’s more, what emerges from many of these scenarios is that including nuclear would make the whole thing harder – more costly, less flexible and less able to balance variable renewables. Basically it’s not needed and gets in the way of the emerging distributed-supply flexible-demand smart grid system.
However, leaving that political battle aside, in terms of the rest of the zero emissions programme, Labour’s approach so far, at least as outlined in the new pamphlet, is a little thin. The party says it wants more public transport — trains and buses — with more electrification to cut emissions, and it is also looking to a major tree-planting programme, working with farmers and foresters to promote biodiversity. These are, arguably, very good ideas, but we will need a lot more detail. Especially now we have the requirements outlined in the new IPCC climate report on 1.5° warming to live up to. I will look at that in my next post, but it suggests that up to 60% of global electricity could come from renewables by 2030 and 85% by 2050.
Silk worms may no longer be alone in spinning a home from scratch. Researchers at MIT in the US have used swarms of robots that can spin tailored fibres in parallel to build architectural scale structures. The work simplifies use of fibre-glass, which can be awkward and expensive to work with, making it easier to exploit the potential anisotropy as well as the impressive mechanical, thermal, water absorption and termite resistant properties of fibre-reinforced composites that make them particularly useful in architecture. The researchers suggest that their swarms of autonomous spinning “fibrebots” that can produce fibre-reinforced composite structures will usher in “the next era of robotic architecture”.
Robot-spun versatility
The basic building components of the structures the fibrebots produce are tubes of fibre-glass thread and photocurable resin. However whereas previous use of robotics in architecture has essentially assembled pre-made components, the spinning robots can build from “a blank slate”.
Previous robotic winding systems that create tubes have had to compromise between tube length with curvature. To get around this trade off the MIT researchers designed robots that produce tubes in segments 90 mm in length and 100 mm in diameter. The robots spin each segment to overlap with the previous at the required angle for the desired curvature before curing, thereby maximizing the versatility of the spinning robots for a range of architectural designs.
More robots make light work
In addition, by programming multiple robots to operate in parallel, the structure designs can exploit the additional load-bearing support and constraint of co-woven tubes. To mitigate against communication challenges and the potential for collision the researchers invoked computations based on Reynold’s flocking algorithms. Artificial life and computer graphics expert Craig Reynolds developed a set of rules for simulating the simultaneous trajectory of multiple simple agents while avoiding collision, just as flocks of birds in flight.
“We augmented the traditional cohesion, separation, and alignment rules with additional user-specified interactions to create designs that allowed habitable spaces and goal-oriented structures, such as bridges, and avoided pre-existing obstacles,” the researchers explain in their report. “These additional rules were incorporated by weighted linear combinations of desired directions that were determined by repulsion or attraction points, which can be time-varying, or a bias among robots to curl around or follow alongside other tubes.”
The researchers demonstrated the potential of their spinning robot swarms in a 4m structure built by 22 of the devices in the space of 12 hours. The structure withstood the brunt of autumn and winter weather to augment the grounds of MIT in New England, USA, for seven months.
Markus Kayser and Levi Cai contributed equally to this work alongside corresponding author Neri Oxman and colleagues at the Mediated Matter Group at MIT, a group that conducts research at the intersection of computational design, digital fabrication, materials science and synthetic biology at scales ranging from the micrometre to full size buidings. They describe the work as “materials ecology”, and the result is a range of biologically inspired and engineered design fabrication tools and technologies and structures that aim to enhance the relation between natural and man-made environments.
A 40-year-old mystery of why mercury nuclei change shape dramatically has been solved by combining data from experiments done at the ISOLDE isotope separator at CERN with supercomputer calculations done in Japan.
Removing just one proton or neutron from an atomic nucleus can sometimes transform it from a sphere to a prolate spheroid that resembles a rugby ball. While such abrupt transitions are rare, they offer physicists the opportunity to study how changes in neutron and proton numbers drive shape changes in nuclei.
The isotopes of mercury are one example where the presence or absence of just one neutron affect the nuclear shape a lot. More than 40 years ago, in one of the first experiments at ISOLDE, physicists discovered that mercury isotopes with 101, 103 and 105 neutrons have strongly prolate spheroidal shapes, while most other isotopes in the 96-136 neutron range are spherical.
Exactly why this occurs has remained unclear for decades because it is extremely difficult to create and study the isotopes. Limits on available computing power also meant that theorists struggled to calculate the properties of these nuclei.
Laser ionization
Now, ISOLDE researchers have looked at mercury isotopes with up to 181 neutrons to gain a better understanding of why the shape-shifting occurs. Using laser ionization spectroscopy, mass spectrometry and nuclear spectroscopy techniques, they found the point at which adding extra neutrons does not result in dramatic changes in shape.
Using these new insights into shape-shifting, theoretical physicists in Japan used supercomputers to do computationally-intensive calculations of the nuclear shell model that provide important insights into the phenomenon. The computations suggest that the shape shifting is related to the excitation of four protons to higher energies than had been considered in previous studies. The four protons combine with eight neutrons to create the rugby-ball shape – which is the lowest energy state for isotopes with 101, 103 and 105 neutrons.
“It is only now, with new developments of ISOLDE’s Resonance Ionisation Laser Ion Source, and by joining forces with other ISOLDE teams, that we have been able to examine the nuclear structure of these isotopes,” says CERN’s Bruce Marsh who is lead author of a paper in Nature Physics that describes the work.
Climate change’s effect on coastal ecosystems is very likely to increase mortality risks of adult oyster populations in the next 20 years.
That is the finding of a new study led by the University of Nantes, the LEMAR (the Marine Environmental Science Laboratory) in Plouzané and the Cerfacs (European center for research and advanced training in scientific computing) in Toulouse (France).
Published today in the journal Environmental Research Letters (ERL), the research highlights a novel and comprehensive relationship between climate variability and historical mortality of adult oysters on the French Atlantic coast from 1993 to 2015.
The team’s results show oyster mortality usually increases after warm and wet winters over Northern Europe, affected by recurrent storms embedded in large weather circulation patterns covering the whole North Atlantic basin – known as the positive phase of the North Atlantic Oscillation (NAO).
The study’s lead author is Yoann Thomas, from the French National Research Institute for Sustainable Development (IRD) at LEMAR. He said: “Benthic species like oysters are keystone species in coastal ecosystems. For example, they build reef habitats, which sustain a high biodiversity, and provide tremendous food source worldwide though fishing or aquaculture activities.
“But they are very sensitive to changes in climate and water quality, because they cannot move if a location becomes inhospitable. In this sense, oyster populations are sentinels of long-term climate fluctuations and climate trends, and more broadly of the ‘health’ of coastal ecosystems.
“We know the NAO is one of the key drivers of ecological variations like species individual growth rate, geographical distribution, phenology and survival. We show that recurrent positive NAO episodes in winter, leading to milder temperatures along the northern European coast, have a long-lasting effect on the biological and environmental factors influencing oyster mortality.
“We also show that the cumulative mortality rate over a year significantly increases after winters dominated by positive NAO. From a practical perspective, this lagged relationship can be used for potential predictability of annual mortality at several months lead-time.”
The researchers linked this climate-related risk to several environmental factors like the unlocking of the winter cold-water barrier for pathogens, the shortening of the resting phase for oyster, and enhanced metabolic rates leading to higher vulnerability in spring and summer.
The storms also caused more fresh water to flow from rivers into the sea, which impacts oysters by lowering the salinity of the water.
By analysing the results of more than 30 climate models and several greenhouse gases emission scenarios, the team used the extreme winter temperatures of the present-day NAO+ climate conditions as an analog to produce forecast assessments of oyster mortality risk factor in the next decades.
Thomas said: “What today are exceptional levels of mortality could become the norm by 2035, even if the global temperature increase is limited to ~2 °C above the pre-industrial period as per the Paris agreement. Natural long-term climate variability on top of anthropogenic-induced warming could ever accelerate or delay the increasing risk by only a decade or so.
He concluded: “The near-future looks bleak, but we show that this will be even worse without a clear reduction of the greenhouse gases emissions by human activities. We obviously need to take rapid action now to avoid further damage to very sensitive and vulnerable coastal ecosystems.”
“It is better to keep the optimism on a low level,” said J Georg Bednorz in 1988. He was speaking to Physics World a year after he and Alex Müller, his colleague at the IBM Zurich Research Laboratory in Switzerland, had been swiftly awarded the Nobel Prize for Physics for the discovery of the world’s first “high-temperature” superconductor. The breakthrough had set alight the condensed-matter community, with many physicists seeing it as the gateway to amazing applications such as lossless transmission lines, high-performance magnets and levitating trains. In the US, Time magazine was heralding “the superconductivity revolution”. Bednorz, on the other hand, was resisting the urge to “promise too much”.
Thirty years on, such restraint seems to have been justified. The field of high-temperature superconductivity has not exploded with applications. Nor, however, has it petered out into irrelevance. Patience has been rewarded by steady improvements in instrumentation and computation, to the point that experiments and theoretical calculations once thought impossible are now routine. And further breakthroughs have come. In the early years, these concerned the notching-up of transition temperatures and the establishment of theoretical approaches. More recently, they have related to the discoveries of entirely new families of superconductor. All in all, the field is “astonishingly different”, says J C Séamus Davis, a physicist at Cornell University in the US. “If we put ourselves back in 1988, what goes on now is inconceivably different to what was happening at that time.”
Disappearing resistance
Superconductivity has captured the imaginations of scientists and the public alike for a very long time. It was in 1911 that the Dutch physicist Heike Kamerlingh Onnes discovered that the electrical resistance of mercury suddenly disappears beneath a temperature of 4.2 K. The development in the 1920s of quantum mechanics, which explained atomic structure, did not, however, immediately provide an answer for this phenomenon in mercury and, later, other metals. Granted, the loosely bound outer electrons of metal atoms can carry a current, but it was believed that at any temperature there always ought to be random thermal fluctuations that keep the current in check. Only in 1957 did three theorists at the University of Illinois Urbana-Champaign in the US – John Bardeen, Leon Cooper and Robert Schrieffer – describe how an electron can deform the atomic lattice through which it moves, thereby pairing with a neighbouring electron. Being paired allows all the electrons in a superconductor to move as a single cohort, known as a condensate, prevailing over thermal fluctuations with ease.
Prize winners: Alex Müller (left) and J George Bednorz. (Courtesy: IBM, courtesy of AIP Emilio Segrè Visual Archives)
Fast-forward to the observations of Bednorz, Müller and those who followed in their footsteps, however, and BCS theory (named after the surnames of its originators) was next to useless. For starters, BCS theory is widely interpreted to limit superconductivity to temperatures less than around 30 K, whereas the superconductors of Bednorz and others were, by 1987, transitioning at 93 K – warm enough to be cooled by liquid nitrogen rather than liquid helium. Moreover, these superconductors were not metals at all but insulators made of copper oxides, or “cuprates”.
The early days of high-temperature superconductivity were mired in inflated language and competitiveness, as physicists strove to rewrite what they thought they knew about condensed matter while often deriding the attempts of rivals who sought to do likewise. Because of the hype surrounding the new field, a 1987 meeting of the American Physical Society (APS) was dubbed the “Woodstock of physics”. Like the original pop-music festival, there were “false starts, confusion and eventually some squabbling” according to a recent account by Reinhardt Schuhmann, an editor at the APS journal Physical Review Letters.
Gradually things settled down. Although physicists did not (and still cannot) settle on an overarching theory of high-temperature superconductivity, they did assemble themselves in two camps: one believing that electrons paired through chemical valence bonds become mobile thanks to doping; and another believing that doping allows for a ripple in an antiferromagnetic alignments of electrons, drawing the electrons together.
A shared sense of mission has been helped by the ability to probe experimentally the electronic and magnetic behaviour of materials with much greater precision, using tools such as resonant inelastic X-ray scattering, angle-resolved photoemission spectroscopy and atomically resolved spectroscopic imaging, to name but three. “These techniques have helped to ‘clean up’ the field: everybody agrees on the landscape of experimental facts,” says Kees van der Beek from the École Polytechnique in Palaiseau, France.
The heat is on
The transition temperatures of the cuprates rose sharply in the late 1980s, then more slowly, to a peak of 135 K (–138 °C) at ambient pressure in the mid-1990s. There ended headline news for high-temperature superconductors until 2008, when Hideo Hosono and colleagues at the Tokyo Institute of Technology in Japan discovered another class of high-temperature superconductors based on iron and arsenic. Known as iron pnictides, these materials have exhibited only relatively low transition temperatures of up to 75 K. Nevertheless, they raised hopes that yet more classes of superconductor could be found, with transitions even closer to room temperature – the field’s primary goal.
As indeed they have been. In 2015 Mikhail Eremets, Alexander Drozdov and colleagues at the Max Planck Institute for Chemistry in Germany discovered that when they squeezed hydrogen sulphide – a substance commonly known for its stench of bad eggs – to pressures of 150 GPa, and cooled it below 203 K (–70 °C), it lost any trace of electrical resistance. The result smashed the previous record for the highest superconducting transition temperature (at high pressure) by 39 K. Even more surprisingly, it threw attempts to untangle the underlying physics of superconductivity up in the air once again, since hydrogen sulphide is conjectured to not be an unconventional superconductor like the cuprates or iron pnictides, but a conventional superconductor in the mould of BCS theory.
In a field that is full of surprises, it seems harder than anywhere else to predict what future developments are in store for high-temperature superconductivity. What is certain is that the recent discoveries of the iron pnictides and hydrogen sulphide have renewed hopes of future breakthroughs. “I am utterly and intimately convinced that room-temperature superconductivity will be discovered,” says van der Beek.
Quietly emerging
Even aside from that room-temperature goal, applications are emerging, if a bit later and with less fanfare than some had expected. High-temperature superconductors have reportedly been employed by the US military in the form of electric motors for propulsion, and as superconducting quantum-interference devices to detect very weak signals from submarines. Energy companies have begun to install them within fault limiters, which restrict electrical currents in the event of power faults; higher superconducting transmission temperatures are important here, because fault limiters heat up during their operation. And cities have begun to see high-temperature superconductors employed as power transmission cables. One of the first, in 2001, was Copenhagen in Denmark, in which a 30 m-long cable was given responsibility for the distribution of power to some 150,000 residents.
In April 2014 a section of power cable based on a cuprate was switched on in the German city of Essen. One kilometre long, it is thought to be the longest high-temperature superconducting cable ever laid in a power grid, designed to eliminate the energy loss associated with regular copper cables. Present at the ceremony was Bednorz, who could finally witness the patience of his approach bearing fruit. “What started to be a dream in the 1980s,” he said, “is now becoming a reality.”
Engineering nanomachines is challenging due to the constantly fluctuating nature of matter at the nanometre scale. Nano-engineers have long dreamed of developing nanoscale motors that can transport nanoscopic cargo along user-specified routes, similar to the transport of passengers and cargo using motorized vehicles.
Now a team of scientists at the University of Oxford has taken a significant leap towards realizing this dream by engineering a molecular “hopper” that can be moved back-and-forth by a user along a pre-defined track. This development enables unprecedented precision in the transport of nanoscale cargo and opens the door to next-generation applications such as high-precision DNA sequencing (Science 10.1126/science.aat3872).
a) The molecular hopper attaches to the track and is driven down it by a user-applied electric field. b) This process takes place within a nanopore. c) The electrodes can also measure current through the nanopore. (Courtesy: Y Qing et al)
The molecular hopper consists of a small molecule body containing a functional group called a thiol (one sulphur atom with a hydrogen attached to it). The body is linked to a piece of molecular cargo; in this case, the cargo was a 40-nucleotide DNA strand, but other types of cargo could be used.
The track consists of five thiol groups patterned in a row (called “footholds”) precisely spaced just 0.7 nm apart from each other. When a hopper encounters a track, the sulphur atoms in the two thiol groups will lose their hydrogen atoms and bind to each other, forming a disulphide bond. The stability of this disulphide bond prevents the hopper from spontaneously popping off the track. However, the hopper can transition between footholds. In the same way that a thiol group can swap its hydrogen atom for another sulphur atom, a sulphur in a disulphide bond can swap its partner sulphur atom for a different sulphur atom, enabling it to move along the track.
To control the direction of a hopper’s motion along a track, the team constrained the track within a protein nanopore and inserted the nanopore into a membrane that separates two fluid compartments. The nanopore is the only hole that connects the two compartments, so a voltage difference between the two compartments (which the researchers generated using a conventional electrode setup) results in an electric field inside the nanopore.
This electric field applies a force to the molecular hopper, shifting its position forward or backward depending upon the direction of the electric field. In other words, a hopper connected to foothold 1 will be pulled closer to foothold 2, significantly increasing its rate of transition from foothold 1 to foothold 2. Then, after the hopper transitions to foothold 2, the electric field will continue to act on it, pushing it closer to foothold 3.
This process will continue until the hopper reaches the end of the track (foothold 5), at which point the researchers could reverse the electric field to make the hopper move backwards down the track. In this manner, the hopper can be moved back and forth across the nanoscale track for hundreds of steps.
The hopper’s motion can be monitored by measuring the current flowing between the two fluid compartments. Because the nanopore is the only path through which current can flow, current measurements are highly sensitive to changes in the position of the hopper. When the researchers applied an electric field and continuously monitored the current, they observed five discrete current levels separated by sharp steps, corresponding to the walker transitioning between the five distinct footholds.
This technology has a promising future. One upcoming application will likely be for DNA sequencing. As a proof-of-concept, the team used three slightly different DNA sequences as molecular cargo and found that they each provided unique current recordings. This was likely due to the sensitivity of current flow through the nanopore to the size and exact chemical structure of the hopper–cargo complex. High-throughput DNA sequencing would likely require the development of longer tracks.
More generally, this work represents a significant advancement in the field of nanotechnology and will help to pave the way for engineered nanomachines of the future.
Primordial black holes do not account for all dark matter, according to new research by Miguel Zumalacárregui and Uroš Seljak at the University of California, Berkeley. The duo has made the best measurement yet of the abundance of black holes in the cosmos by measuring the gravitational lensing of light from type 1a supernovae. Their study puts an upper limit of 40% on how much dark matter can be accounted for by primordial black holes
For decades, physicists have grappled with growing evidence that the formation and dynamics of galaxies and larger structures in the universe are governed by gravitational forces from unseen dark matter. While the mysterious substance appears to account for about 85% of all matter in the universe, dark-matter particles have yet to detected directly.
While most astrophysicists believe that dark matter is some sort of exotic particle, another explanation – first put forth in 1974 by Stephen Hawking – is that primordial black holes could account for some dark matter. Such black holes could have formed in the early universe and could have masses that range from just millionths of a gram to billions of solar masses. They are not expected to be surrounded by radiation-emitting disks of gas and dust – which would make them dark and very difficult to detect.
Bending starlight
One way of testing Hawking’s hypothesis is gravitational lensing. This occurs when a massive object such as a black hole lies between the Earth and distant star. The gravitational field of the black hole bends the starlight towards Earth, making the star appear brighter. The idea is that as primordial black holes move across our view of distant stars, the light we observe should fluctuate over relatively short timescales. Lensing studies have already ruled out the existence of large numbers of primordial black holes that range in size from the very tiny to about 10 solar mases.
More massive primordial black holes, however, are difficult to study in this way because the light fluctuations occur over timescales of decades – making astronomical observations impractical. As a result, astronomers have been unable to search for larger primordial black holes.
To get around this problem, Zumalacárregui and Seljak looked at light from gravitationally-lensed type 1a supernovae. Dubbed “standard candles”, these exploding stars give off light at a very specific brightness that fades over time in a very specific way. When viewed through a gravitational lens, the relationship between the brightness of the supernova and the rate at which it fades should be different than that seen in a supernova that is not lensed. This should reveal the presence of large primordial black holes without the need for long observation times.
Zumalacárregui and Seljak analysed observations of 1300 supernovae and found no objects with an unusual brightness-fading relationship. This allowed them to conclude that there cannot be a sufficient number of primordial black holes with masses greater than 0.01 solar masses to account for all dark matter in the universe. Instead, they say primordial black holes could account for at most around 40% of dark matter. The result confirms the importance of continuing the search for as-yet unobserved sources of dark matter, including elementary particles such as WIMPs, sterile neutrinos and axions.
William Nordhaus (Courtesy: Ill. Niklas Elmehed. Nobel Media)
The 2018 Nobel Prize in Economic Sciences has been awarded jointly to William Nordhaus of Yale University, US, for “integrating climate change into long-run macroeconomic analysis” and Paul Romer of New York University, US, “for integrating technological innovations into long-run macroeconomic analysis”.
“This year’s prize rewards the design of models and methods to address some of the most fundamental and pressing questions of our time, involving the long-run development of the global economy and the welfare of its citizens,” writes the Royal Swedish Academy of Sciences’ backgrounder on the prize. “Paul M Romer has given us new tools for understanding how long-run technological change is determined in a market economy, while William D Nordhaus has pioneered a framework for understanding how the economy and climate of our planet are mutually dependent on each other.”
Romer and Nordhaus will each receive half of the 9 million Swedish krona prize.
According to the Academy, in his focus on the fundamental challenges of climate change, Nordhaus has stressed important negative side effects – and thus the restrictions – of the endeavours to bring about future prosperity. “Both Romer and Nordhaus emphasize that the market economy, while a powerful engine of human development, has important imperfections and their contributions have thus offered insights into how government policy could potentially enhance our long-run welfare,” the backgrounder writes. “…Looking forward, the combined work by the Laureates offers the research community an opportunity to address long-run issues around climate, energy supply and sustainability, by studying government policy together with endogenous technological change in the global market economy.”
Beginning in the 1970s, Nordhaus studied economic growth and natural resources, the economics of climate change, and resource constraints on economic growth. He developed the integrated assessment model, making economic and climate models compatible to investigate how fossil fuels burnt for economic use give off carbon emissions that raise atmospheric concentrations of carbon and boost global temperatures, in turn causing economic harm.
Nordhaus created the DICE (Dynamic Integrated Climate-Economy) and RICE (Regional dynamic Integrated Climate-Economy) models to determine efficient paths for coping with climate change. These models were the foundation for integrated assessment models used by the Intergovernmental Panel on Climate Change, by the US Environmental Protection Agency to estimate the social cost of carbon, and in Nicholas Stern’s review of the economics of climate change for the UK government in 2007.
Nordhaus currently directs the G-Econ project, which provides the first comprehensive measures of economic activity at a geophysical scale. His most recent book The Climate Casino: Risk, Uncertainty, and Economics for a Warming World came out in 2013.
Romer’s work on drivers for knowledge creation is also relevant to the way we deal with climate change. “It is entirely possible for humans to produce less carbon,” he said at the press conference announcing his Prize in Economic Sciences, according to the official Nobel twitter stream. “Once we start to try to reduce carbon emissions, we’ll be surprised that it wasn’t as hard as we anticipated.”
This news story is based on press releases from the Royal Swedish Academy of Sciences and Yale University.
A recently discovered form of lignin known as catechyl (or C-) lignin could be used in biorefineries to produce biofuel. This is the new finding from a team of researchers at the University of Wisconsin-Madison who say that C-lignin can be readily processed to yield 90% of valuable commodity chemicals – something that is unimaginable for ordinary lignin.
Lignin is a major component of plant biomass and the most abundant source of renewable aromatics (carbon-based materials usually derived from petroleum). The problem is that it is difficult to produce sugars for biofuels, and then valuable products, from the lignin residue because it contains several types of monomers and distorts when chemically processed. Paper factories, for example, often simply incinerate it and use it for fuel rather than try to convert it into commercial bioproducts.
Researchers led by John Ralph of the Great Lakes Bioenergy Research Center and the Wisconsin Energy Institute are now saying that there exists a natural form of lignin from which it is possible to obtain 90% yields of phenolic (catechol-type) monomers with a single compound accounting for most of the product.
“We’ve come up with ‘ideotype’ for lignin, that is, an archetype for a lignin that is ideal for the biorefinery,” Ralph tells Physics World. “This C-lignin can be readily processed to produce potentially valuable commodity chemicals in high yields.”
What is C-lignin?
C-lignin is essentially a benzodioxane homopolymer and derives from caffeyl alcohol, a hydroxycinnamyl alcohol that is not one of the normal monolignols (sinapyl, coniferyl and p-coumaryl alcohols) from which lignin is usually derived in plants, he explains. “Together with colleagues at the University of North Texas, we originally discovered this unusual lignin in the seed coats of vanilla.”
“In previous research, we unexpectedly found that caffeyl alcohol undergoes the radical coupling that characterizes lignification in essentially only one way – by so-called β-O-4 coupling. The result is C-lignin – a linear and homogenous polymer with only one kind of interunit (ether) linkage, which means that it can be cleanly cleaved into monomer units (using a simple depolymerisation chemical treatment). These ‘building blocks’ can be transformed in different ways to produce a variety of products.”
Another good thing about C-lignin is that its structure remains stable after chemical pre-processing unlike ordinary lignin, explains study first author Yanding Li. This is because it contains a 3-OH groups instead of the usual 3-OMe ones. These allow for an internal trapping reaction post-radical coupling that re-aromatizes the intermediate product to produce benzodioxane rings in each unit instead of the normal β-ether (which has a non-cyclic sidechain), protecting the sensitive benzylic-OH.
“When plants are refined into biofuels, the lignin first gets stripped away, leaving sugars to be converted into the bioproducts. This pre-treatment usually causes lignin to ball up into a tangled mess. C-lignin’s structure survives even the harshest pre-treatments, however, and it is even resistant to concentrated sulphuric acid.”
Yanding Li
90% yield
In their experiments, Ralph, Li and colleagues subjected C-lignin to hydrogenolysis – a technique to deconstruct lignin developed at UW-Madison back in 1938 by the chemist Homer Adkins. The technique produces a simple pair of monomers in 90% yield. “Choosing the right catalysts can narrow this down to a single monomer,” says Ralph.
“Our work provides a new way to produce chemicals and intermediates, such as catechols, sustainably form natural resources and we hope that it will spur interest in using such compounds to produce polymers and bioproducts. It could also allow researchers to think further about how other lignins might be used in bioprocessing.”
The team, reporting its work in Science Advances 10.1126/sciadv.aau2968, says that it is now working on isolating the genetic code of C-lignin and inserting this lignin into “normal” bioenergy crop plants that might then be cultivated on a large scale. “To date, genetic engineering attempts to do this have not been particularly successful,” says Ralph
“We are also trying to produce C-lignin from other biomass waste sources,” he reveals.
