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What are the conditions for life to exist on distant planets?

Whether or not we are alone in the universe is one of the most profound questions that humanity can ask. In this short video David Kipping, an astronomer at Columbia University in the US, takes a fresh look at the conditions required to support life. Specifically, Kipping takes issue with the definition of the so-called “habitable zone” – the band surrounding a star within which water could exist in liquid form on the surface of a planet. Kipping points out that the requirements for life are complex and this definition is based on the fact that all known life forms here on Earth require water. What if that is not universally true?

This video is part of our 100 Second Science series, in which researchers give concise presentations covering the spectrum of physics.

Flash Physics: Spider inspires structural colour, the roundest star, quantum simulator is very fast

Spider and flowers inspire new structural colour

A blue spider has inspired researchers to create a new material with structural colour that does not change with the viewing angle. Materials with structural colour get their hues from the interference of reflected light from tiny structures. Some structural colour – such as seen on the feathers of some birds or the reflection from a CD – is iridescent, which means that the observed colour changes with the angle of observation. Other naturally occurring structural colour remains constant irrespective of the observer, and it is this type of structural colour that researchers have struggled to recreate in the laboratory. Now, Radwanul Hasan Siddique and colleagues at the Karlsruhe Institute of Technology in Germany have teamed up with researchers in the US and Belgium to create a material that has a structural colour that is the same when viewed over 160°. Resembling an array of tiny flowers – each about 15 μm across – the material has a hierarchical structure that has translational and rotational symmetries at a number of different length scales (see image above). This geometry ensures that there are no special directions in how light is reflected. The material was inspired by the blue tarantula, which has non-iridescent structural colour. The material is described in Advanced Optical Materials and its colour can be adjusted by changing the size of the flowers. The researchers believe it could be an important step towards creating non-toxic, vibrant and durable colours for textiles and other applications.

Astronomers spot the roundest natural object in the universe

The star Kepler 11145123 is the roundest natural object ever measured in the universe
The star Kepler 11145123 is the roundest natural object ever measured in the universe. Stellar oscillations imply a difference in radius between the equator and the poles of only 3 km. This star is significantly more round than the Sun. (Courtesy: Laurent Gizon et al., Max Planck Institute for Solar System Research. Illustration by Mark A Garlick)

Consider a spherical star in the vacuum of outer space. Thanks to recent observations made by a team of researchers at the Max Planck Institute for Solar System Research (MPS) and the University of Göttingen, both in Germany, this may no longer be a hypothetical scenario. Most stars are not perfect spheres – their shape is determined by their rotation speeds: the faster the rotatation, the more oblate the shape. But as stars appear to us as mere points on the sky, their shapes are difficult to measure. Now, a team led by Laurent Gizon at MPS has, for the first time, measured the oblateness of a star, with unprecedented precision. Gizon and colleagues used “asteroseismology” or the study of the oscillations of stars. The applied the method on a slowly rotating star (Kepler 11145123), which is some 5000 light-years from Earth. They found that the difference between the equatorial and polar radii of the star is only 3 km – a very small amount compared to the star’s mean radius of 1.5 million km. Kepler 11145123 rotates at one third the angular velocity of the Sun, which rotates once every 27 days. The distant star also supports only sinusoidal oscillations, meaning its periodic expansions and contractions can be detected via its luminosity. NASA’s Kepler mission observed the star’s oscillations continuously for more than four years and found the virtually negligible difference in radius. “This makes Kepler 11145123 the roundest natural object ever measured, even more round than the Sun,” says Gizon. The work is described in Science Advances.

Quantum simulator is very fast

A team of physicists is claiming the record for the world’s fastest quantum simulator. The system involves cooling an ensemble of about rubidium-87 atoms to a temperature of about 70 μK. The atoms are then put into highly excited Rydberg states by firing an ultrashort 10 ps (10–11 s) laser pulse at the ensemble. Rydberg atoms have very large radii and therefore will interact very strongly with each other. This ensemble can then be used to simulate strongly correlated quantum systems such as electrons in superconductors and magnets. In the team’s experiment, a first pulse is followed by a second 10 ps pulse, which is used to measure how the atoms are interacting with each other. The time delay between the pulses can be controlled on the 10 as (10–17 s) scale and this allowed the researchers to observe a coherence oscillation in the gas with a period of 1 fs (10–15 s). The research is reported in Nature Communications and has been done by an international team that included Nobuyuki Takei and Christian Sommer of the National Institutes of Natural Sciences in Okazaki, Japan.

 

  • You can find all our daily Flash Physics posts in the website’s news section, as well as on Twitter and Facebook using #FlashPhysics.

How weather became a science

Meteorology was not always a science. In 1846 François Arago, director of the Paris Observatory and permanent secretary of France’s prestigious Académie des Sciences, declared “Whatever may be the progress of sciences, never will observers who are trustworthy, and careful of their reputation, venture to foretell the state of the weather.” Arago and his fellow 19th century “gentlemen scientists” considered weather forecasts no different from prophecies delivered by soothsayers – an attitude that damaged the reputation of many who were sincerely trying to understand how the atmosphere worked.

Shortly after the turn of the century, however, meteorology began to modernize. This era, from around 1900 to 1960, is the focus of James Fleming’s book Inventing Atmospheric Science. Fleming is a historian of science and technology at Colby College in Maine, US, and also the founder and first president of the International Commission on the History of Meteorology. Following an undergraduate degree in physics and a Master’s in atmospheric science, he has become one of meteorology’s most influential historians. His many well-researched and compelling books include a biography of Guy Stewart Callendar, who first demonstrated the effect of carbon-dioxide emissions on the climate (The Callendar Effect, 2007) and a history of “weather engineering” schemes and their false promises (Fixing the Sky, 2010). Although modern meteorology had many important forebears, in Inventing Atmospheric Science Fleming singles out three and wraps a surprisingly coherent narrative around them.

The first of Fleming’s inventors is Vilhelm Bjerknes (1862–1951), an ambitious Norwegian physicist who began his career by pursuing his father’s research interests in fluid dynamics. During the First World War, while seeking to help his native country survive food shortages, Bjerknes realized that physics had immense practical value for weather forecasting: at its heart, meteorology was simply an initial value problem. But Bjerknes did not just apply his physical insight to develop a weather-forecasting service in Bergen. He was also adept at the practical aspects of running such a service (obtaining data, issuing forecasts); politically astute enough to gain national support and resources; and skilled enough to manage a research group.

This group made several important discoveries, including the “polar front”, a globe-girdling region of enhanced temperature gradient that drives much of the weather of the mid-latitudes. Group members also crafted a conceptual model for the evolution of extratropical cyclones. Both developments, Fleming writes, served as vehicles for Bjerknes’s ambition. While there are other books and articles about Bjerknes (notably Robert Marc Friedman’s Appropriating the Weather), Fleming succeeds in shedding new light on his subject, including details on the friction between the Bergen group and a rival Austrian school, and also an account of the American Weather Bureau’s resistance to the Bergen methods.

One of Bjerknes’s most renowned group members was Carl-Gustaf Rossby (1898–1957), the second figure in Fleming’s study. After studying in Bergen, Rossby came to the US on an American–Scandinavian Foundation fellowship. Instructed to bring the Bergen methods to the Weather Bureau (now the National Weather Service), Rossby proved not only an excellent researcher (he developed the Rossby wave equation to calculate the motion of undulations in the jet stream), but also an inspirational leader. After leaving the Weather Bureau, he founded the first graduate school in meteorology at the Massachusetts Institute of Technology; chaired the newly formed Institute of Meteorology at the University of Chicago; and founded two extant scientific journals: the American Meteorological Society’s Journal of Meteorology (now Journal of the Atmospheric Sciences) and the Stockholm International Meteorological Institute’s Tellus. Rossby was also instrumental in working with the teams that produced the first computerized weather forecasts on two continents. This chapter of the book is the shortest of the three; however, I had the sense that more depth was needed to explain how Rossby accomplished all these things with such apparent ease.

A five-minute visit with Rossby was all it took to inspire Fleming’s third protagonist to study meteorology. Harry Wexler (1911–1962) rapidly advanced in his career to become head of research at the Weather Bureau. Despite dying at the young age of 51, Wexler was involved in some of the biggest advances in atmospheric science, including weather radar, computerized weather prediction and satellites. In his short life, he also became the first meteorologist to fly into a hurricane; was appointed chief scientist of the International Geophysical Year in 1957/8; and established the carbon-dioxide measurements at Hawaii’s Mauna Loa volcano, which have been crucial in demonstrating the influence of human activities on the atmosphere. This chapter is probably the one that most meteorologists will appreciate. Wexler is the least known of the three, yet his contributions on such a range of topics were significant. Kudos to Fleming for finally telling Wexler’s story.

Bringing Inventing Atmospheric Science to a close, Fleming argues that 1957 was the turning point when atmospheric science became “big science”, less focused on individuals and more run by committees and national research organizations. Here, the emphasis is on the US with its national investment in science and the creation of the National Center for Atmospheric Research in Boulder, Colorado. This part of the story is especially germane because Bjerknes, Rossby and Wexler were each masters of building structures and leading organizations, and it is these structures that would become critical to the subsequent evolution of atmospheric science as its own discipline, as Fleming adeptly argues.

Although we learn a lot about the accomplishments of these three giants, Fleming delivers few insights into what they were like as people. Personal stories and their non-science lives are rarely described, which makes Inventing Atmospheric Science relatively short (only 226 pages of text in the chapters). Some of the terminology (and many of the more peripheral actors) described in the book might not be recognizable to a non-atmospheric scientist, but that shouldn’t diminish the book’s readability. Almost anyone with a background in science – and especially those interested in the foundations and evolution of a discipline – should be able to understand most of the book. This book also introduces physicists to some of the great scientist–leaders who created the field of atmospheric science. Indeed, few other disciplines can claim to have undergone such a radical change, from soothsaying in the 1800s to the rigorous field of predicting the future that is modern atmospheric science.

  • 2016 The MIT Press £22.95/$31.00hb 312pp

New aeroplane wing changes shape to boost performance

A new type of composite wing that can change its shape according to flight conditions has been made from a lattice of small, lightweight components. This morphing ability could allow for more aerodynamic, manoeuvrable and fuel-efficient aircraft that are also simple to construct. Described as a “digital-material” approach to aeronautical design, the technology was developed by a collaboration involving NASA and several US universities, and could be applied to a variety of other structures from bridges to wind turbines.

Most aeroplanes have fixed wings that are fitted with ailerons, which are hinged control surfaces used to manage the lift and roll throughout the flight. The shape of fixed wings, however, is always a compromise in efficiency with different wing configurations being more suitable for different speeds and flight paths. Because of this, the concept of a wing that could change shape during flight has always been something of a holy grail for aircraft engineers – not the least because this could lead to much greater fuel efficiency.

Attempts to achieve this, however, have been unsuccessful. This is largely because the typical approach to wing deformation relies on the use of mechanical control structures that are simply too heavy to improve the overall efficiency of the wing. This new morphing design takes a different approach in which the entire wing becomes the deformation mechanism. Motors in the aircraft fuselage apply a pressure to each wing, which then twists uniformly along its length.

Lightweight lattice

The morphing wing is made from a lattice of lightweight, flexible, centimetre-scale, carbon-fibre-reinforced polymer components. These are assembled, like a child’s construction set, into larger structures. While each component is strong and stiff, the overall flexibility of the structure can be tuned by varying its overall shape, as well as the shape and exact composition of its individual components. The wing is completed with an outer skin of overlapping, flexible polyimide pieces that cover the lattice structure – much like scales on a fish.

The digital-materials approach “presents a general strategy for increasing the performance of highly compliant – that is, ‘soft’ – robots and mechanisms,” says team-member Kenneth Cheung, who is an engineer at NASA’s Ames Research Center in California.

Testing the wing design in a wind tunnel, the researchers found that the new wings can both match the aerodynamic properties of a conventional, fixed wing and deform in such a way that replaces the need for trailing-edge ailerons – but with only a tenth of the weight of a fixed wing. Following these tests, the researchers developed a small, unmanned aircraft, which has demonstrated excellent manoeuvrability (see image above). While such craft could pave the way for enhanced drones, the wing designs could also be scaled up for larger aircraft, Cheung says.

Made by robots

While the wings used in the studies so far have been assembled by hand, the team is also collaborating on the design of miniature robots that could assemble – and even examine and repair – such structures automatically. The wing’s composite nature should allow for simpler construction and repair processes – and could even allow the wing to be broken down into its component parts and re-used for some other purpose.

“Digital materials and fabrication are a fundamentally new way to make things and enable the conventionally impossible,” says Gonzalo Rey, chief technology officer for the aerospace-engineering company Moog, who collaborates with the researchers. The concept, he adds, has far broader potential, and could extend to such structures as flexible robots, bridges and skyscrapers, “providing not only improved performance and survivability, but also a more sustainable approach by achieving the same strength while using, and reusing, substantially less raw material”.

Other potential applications for digital materials include the in-situ fabrication of wind-turbine blades and space structures – both of which are expensive and logistically complicated to transport in their completed form to their place of operation.

New concept

Jianguo Zhao – a mechanical engineer at the Colorado State University, who was not involved in this study – says that the idea of using lightweight, tuneable cellular solids is a new concept in this area. He adds: “I am looking forward to see if the group can [use] this technology to fabricate airplanes with morphing wings that can fly freely, which might transform the traditional way to design and manufacture aircraft.”

The researchers are now working to better understand the failure modes of their digital materials, with a mind to optimizing their robustness. They are hoping to develop and test a complete aircraft that is designed from the top down with their new construction strategy – along with exploring the potential to develop various other modular structures and integrated robotics.

The research is described in Soft Robotics.

Flash Physics: New solar-energy model, Persis Drell named Stanford provost, gas sensors in a jiffy

Solar-energy computer model available to public

A computer model that predicts the energy output of solar-energy systems has been made freely available to the public by its creators at the Solar Energy Institute of the Technical University of Madrid, Spain. When a solar-energy system is installed at a specific location, precise local information about annual solar-radiation levels and ambient temperatures are needed to make accurate predictions of how much energy will be generated. Often this information is not available for new sites, which is where the software comes in. The online version of the software is called SISIFO and it uses available meteorological and other information to predict energy output for timescales as short as seconds, which allows the real-time performance of a facility to be predicted. Its creators say that the model has been compared with data from more than 200 weather stations and the deviations have been found to be less than 2%.

Physicist Persis Drell named next Stanford provost

Photograph of Persis Drell
Persis Drell will be the next provost of Stanford University. (Courtesy: Saul Bromberger and Sandra Hoover)

Physicist Persis Drell will be the next provost of Stanford University in the US. Drell is the current dean of the Stanford School of Engineering and was previously director of the SLAC National Accelerator Laboratory. Her appointment, recently announced by Stanford president Marc Tessier-Lavigne, will take effect on 1 February 2017. The provost serves as the chief academic officer and chief budgetary officer for the university and works in close partnership with the president to provide overall leadership for the campus. “Persis is a bold, visionary, inclusive and collaborative leader who has demonstrated the capacity and versatility to quickly master complex leadership roles,” says Tessier-Lavigne. He adds that Drell is an “enthusiastic and dedicated citizen of the Stanford community, widely known for her warmth and spirit”. Drell, 60, grew up on the Stanford campus – her father was well-known theoretical-physicist Sidney Drell – and was the first woman to head SLAC as well as the first to be dean of the Stanford School of Engineering. “For me, this is about helping our students achieve their potential to lead fulfilling lives and have an impact on the world,” says Drell. She adds that she will support “our faculty in doing the brilliant research and teaching that also have an impact on the world, and addressing issues important to our community, including moving toward a professoriate that reflects our student body”.

Production time cut for nanostructure gas sensors

An array of molybdenum-trioxide nanorods
An array of molybdenum-trioxide nanorods that were created in a rapid, one-step process. (Courtesy: Osaka University)

A simple and quick way to produce gas sensors based on tiny nanostructures has been developed by researchers in Japan. Gas sensors based on semiconductor nanostructures have been around for a while and are used in a range of applications including analysing human breath samples. They work by detecting the changes in electrical conduction that occur when molecules of interest adhere to the surface of a superconductor. The sensitivity of such a detector increases with the surface area available for adhesion and surfaces patterned with nanostructures offer an extremely large surface area. However, creating nanostructure patterns involves a number of complicated and time-consuming manufacturing steps. Now, Tohru Sugahara and colleagues at Osaka University have cut the time needed to make nanostructured sensors for detecting volatile organic compounds (VOCs) by a factor of 10. Their one-step fabrication process involves placing a precursor material on a substrate and heating it to produce an array of molybdenum-trioxide nanorods. The researchers say that they are able to create VOC sensors with responses comparable to “top-of-the-line” sensors made using traditional methods.

 

  • You can find all our daily Flash Physics posts in the website’s news section, as well as on Twitter and Facebook using #FlashPhysics. Tune in to physicsworld.com later today to read today’s extensive news story on a new type of aeroplane wing.

Gold nanospheres confine light to smallest volume ever

Light has been confined to volumes smaller than the size of a single atom for the first time. The feat, which seemed completely impossible even just a few years ago, has been achieved by researchers in the UK and Spain. They say that the “picocavity” that confines the light can be thought of as the world’s smallest magnifying glass. It could be used to study how light and matter interact at tiny scales and even to observe individual chemical bonds forming and breaking between atoms. The technique could also be used to make new optomechanical data-storage devices in which information can be written and read by light and stored in the form of molecular vibrations.

For a long time, scientists thought that visible light could not be focused to a spot that is less than half its wavelength – the so-called diffraction limit. In recent years, however, they have learnt how to use nanostructured metals like gold and silver that support surface plasmons (oscillations of electrons at the metal surface) to confine optical fields to much smaller spaces than their wavelength in free space would allow.

Now, a team led by Jeremy Baumberg at the University of Cambridge in the UK has used gold nanoparticles to make the world’s tiniest optical cavity. This cavity is so small that only a single atom can fit in it. “We will never do any better than this,” says Baumberg.

A nanoparticle-on-mirror

The researchers made their cavity in two steps. First, they made a sandwich structure that they called a nanoparticle-on-mirror. To do this, they lay down a flat mirror of gold and then coated it with a layer of molecules that like to stick to it. On top of this, they scattered gold particles that are 80 nm across and nearly spherical.

“This structure confines light with a specific red colour that is resonantly trapped in the gap between sphere and mirror,” explains Baumberg. “However, the light confined here is still a hundred times larger than we want.

“The next stage is more magical,” he continues. “We have been trying to understand how these samples behave, so we cooled them down to liquid-helium temperatures (10° above absolute zero) to try and stop all motion of molecules and atoms. Then, when we shone laser light on them, we noticed a peculiar thing.

“Occasionally, the light scattered from molecules became thousands of times stronger for many seconds, before disappearing. We found that what happens is that individual molecules from the gold are pulled by the light out of the bulk facet to sit on the surface. These atoms stuck on the flat surface act a little like lightning rods (but for light, not static electric fields) and trap light just above their tip. The trapped light has a volume of less than 1 nm cubed, so we call it a picocavity.”

Observing single bonds

Since the volume of this cavity is so small, it takes light almost no time to circulate around it, he adds. This increases all of the interactions between the light and the objects inside – in this case, biphenyl-4-thiol molecules. “It is also so small that it preferentially interacts with just a single bond within a molecule, allowing us to study it better. We can see that as we shine more light on it, we set the bond vibrating harder, and the molecule starts to deform.”

According to the team, which includes researchers from the Center for Materials Physics in San Sebastian in Spain, the new cavity could be used to study how molecules and metal atoms behave at very short length scales. This is very hard to do under ambient conditions with electron microscopy, for example. “Here, we directly see their motion in real time,” Baumberg tells nanotechweb.org. “We hope that this will allow us to understand how chemical reactions work for molecules attached to surfaces,” explains Baumberg, adding “This is of major importance for all the chemicals we use as a society today, since they are made using catalysis at a metal surface.”

Changing colour

Baumberg also points out that the ultrasmall-sized cavities “provide us with a way of making optoelectronic switches that change colour when we inject just a tiny amount of energy into the picocavity – either by light or electricity”.

Writing in Science, the researchers say they are now busy looking at what happens when they increase the laser power and how they can start to bend and break the molecules. “We are also trying to understand how light moves around the gold atoms and if we can control this with much more precision, to build objects on the nanoscale,” says Baumberg.

Flash Physics: Asteroid missions, mathematical physicist bags C N R Rao Prize, ultrashort electron emission

“Small-body scientists” call for more asteroid missions

More than 100 planetary scientists have signed a letter calling for more space missions to study asteroids and other near-Earth objects. The “small-body scientists” emphasize the need for the Asteroid Impact Mission (AIM), which is currently a proposal being evaluated by the European Space Agency (ESA). AIM has been proposed for inclusion in the Asteroid Impact and Deflection Assessment (AIDA) mission, which could be launched in 2020 by ESA and NASA. AIM would travel to a binary asteroid system called Didymos, where it would study the smaller asteroid in the system. This smaller asteroid is about 150 m across and is of interest to scientists because it is about the same size as most asteroids that could potentially strike Earth. AIM would also stick around to watch as the Double Asteroid Redirection Test (DART) – also part of AIDA – smashes into the smaller asteroid to see if it is possible to deflect an asteroid on a collision course with Earth. The signatories point out that we currently know of more than 1700 asteroids that are considered hazards because they could collide with Earth. “Unlike other natural disasters, this is one we know how to predict and potentially prevent with early discovery,” they write.

Mahouton Hounkonnou bags 2016 C N R Rao Prize

Mahouton Norbert Hounkonnou, a professor of mathematics and physics at the University of Abomey-Calavi in the Republic of Benin has won the 2016 C N R Rao Prize for Scientific Research. The prize, which is awarded by The World Academy of Sciences (TWAS) in Italy, recognizes Hounkonnou’s “outstanding level” of research in mathematics and his sustained commitment to mathematics education. He was given the prize “for his incisive work on noncommutative and nonlinear mathematics and his contribution to world-class mathematics education”. Hounkonnou’s research has seen applications in a variety of fields including physics, oceanography, health, the management of water and ecosystems, climate studies and energy policy. The prize was announced yesterday during the opening ceremony of the 27th General Meeting of TWAS. The prize – which is named after and provided by TWAS founding fellow and chemist C N R Rao – aims to recognize high-impact scientific work done by researchers from Least Developed Countries. “For me it is an important recognition of more than 20 years of research activity,” says Hounkonnou. “At the same time, it is a sort of encouragement and motivation to continue in the same direction, doing good research and promoting younger people in science,” he adds.

Laser pulses control electron emission with femtosecond timing

Artist's impression of the electron switching mechanism
Impeccable timing: artist’s impression of two laser pulses (red and blue) ejecting electrons (green) from a tiny metal tip. (Courtesy APS/Alan Stonebreaker)

A method for switching a source of electrons on and off on the femtosecond (10–15 s) timescale has been developed by Michael Förster of Friedrich-Alexander University in Germany and colleagues. It involves firing two laser pulses at a nanometre-sharp metal tip to excite electrons out of the metal. One pulse is relatively bright and at frequency ω, whereas the other is relatively dim and at frequency 2ω. There are two different ways that electrons in the tip can absorb energy from the pulses and be emitted into the vacuum. Quantum interference between these two pathways can either switch the emission on or off, depending upon the phase difference between the ω and 2ω light. Förster and colleagues report that electron emission can be switched off in 10 fs or shorter by adjusting the phase difference. Electron sources based on the effect could find use in ultrafast electron microscopes, tabletop particle accelerators and intense sources of X-rays. The technique is described in Physical Review Letters and could also be used to measure the phase difference between laser pulses.

 

  • You can find all our daily Flash Physics posts in the website’s news section, as well as on Twitter and Facebook using #FlashPhysics. Tune in to physicsworld.com later today to read today’s extensive news story on the “world’s smallest magnifying glass” .

Schistosomiasis parasite moves using an unusual swimming stoke

The parasite that causes the tropical disease schistosomiasis exploits a unique elasto-hydrodynamic coupling that allows it to swim extremely efficiently, according to a team of researchers in the US. The parasite’s larva relies on being a good swimmer to infect humans, so the team hopes that its findings will lead to interventions that hinder its movement and reduce infections.

Schistosomiasis is a parasitic disease caused by blood flukes of the genus Schistosoma. According to the World Health Organization, an estimated 258 million people, mainly in Africa, required treatment for the disease in 2014, although only 20 per cent of those received it. Like most neglected tropical diseases, schistosomiasis mainly affects people living in poverty.

Infections occur when people enter water that contains the free-swimming larval stage of the parasite, which is released by freshwater snails. The larvae look for humans, pierce their skin and then migrate to blood vessels where they develop into adults. Adult females then release eggs that either pass out of the body – in faeces or urine – and infect snail hosts or become trapped in body tissue, causing disease.

Poverty trap

Common symptoms of schistosomiasis include abdominal pain, diarrhoea and blood in stools and urine. It has a significant economic impact because chronic infection can affect people’s ability to work, trapping families in poverty, and childhood disease can impact learning, as well as causing anaemia and stunted growth. An estimated 20,000 people die every year as a result of schistosomiasis. Although treatment is available, people are often re-infected because they cannot avoid contact with contaminated water.

The larvae only have 12 h to find a human – or else they perish, because they cannot feed
Grace Presley

Manu Prakash, a bioengineer at Stanford University, told Physics World that once the larvae leave a snail “they only have 12 h to find a human – or else they perish, because they cannot feed”. “This insight told us that swimming efficiency and mechanisms must be important for the disease infection cycle.” To help them understand how the parasite larvae swim, Prakash and his colleagues studied live specimens using high-speed cameras that collected up to 2000 frames per second, and built mathematical and robotic models of the larvae.

The larvae are around 500 μm long and have a head and a slender tail that splits into a two-pronged fork at the end. This unusual fork is not seen in any other well-studied swimming micro-organisms. The researchers identified three different swimming gaits, each with different positioning of the fork. The most significant of these was a tail-first technique that the parasites used to swim upward against gravity, to get them closer to the water’s surface where they are more likely to find a human host. For most of this stroke, the fork sits perpendicular to the rest of the tail, creating a “T” shape.

Symmetry breaking

Because of its small size, the parasite is a low Reynolds-number swimmer, which means that viscous forces dominate its motion and inertial forces are not important. When the researchers studied the “T-swimming” technique, they discovered that the parasite uses an unusual method to break time-reversal symmetry.

During this gait the larvae beat their tails from side-to-side, while maintaining an increased flexibility at the joint at each end. According to the researchers, this creates an unusual elasto-hydrodynamic effect “where the tail provides the energy for propulsion but no thrust, while tail-head and tail-fork joints act as passive torsional springs providing all the thrust”. Prakash explains that the “tail acts as a torsional elastic joint” and there is an elasto-hydrodynamic coupling with “the elasticity of this torsional spring balancing the hydrodynamic drag force that acts on the fork”.

Low-energy mechanism

This creates a very simplistic, low-energy mechanism where the only control comes from tuning the flexibility of the joints. The mathematical models and robot larvae that the team built show that the joint stiffness ratios used by the parasite larvae provide the most efficient swimming stroke possible.

Prakesh told Physics World that his team is now looking to exploit its understanding of the larva’s swimming technique to tackle schistosomiasis transmission. Indeed, the researchers have just returned from a field trip where they were looking at how the parasite larvae swim and find hosts in open-water bodies. The research is described in Nature Physics.

Flash Physics: IOP honours six physicists, APS retracts Trump statement, quantum physicists advise World Economic Forum

Institute of Physics names six new honorary fellows

The director-general of CERN Fabiola Gianotti and James Hough of the University of Glasgow – who played an important role in the recent detection of gravitational waves – have been named honorary fellows of the Institute of Physics (the IOP). The fellowship is the highest honour bestowed by the UK-based IOP and this year’s new fellows also include former IOP president (2013–2015) Frances Saunders, who lead the UK’s Defence Science and Technology Laboratory in 2007–2012. Optics-pioneers John Pendry of Imperial College London and Wilson Sibbett of the University of St Andrews also gain honorary fellowships, along with Neil Turok, who is director of the Perimeter Institute in Canada and founder of the African Institute for Mathematical Sciences in South Africa. The fellowships will be conferred on 29 November.

American Physical Society retracts Trump statement

Following criticism from some of its members, the American Physical Society (APS) has retracted a press release – which it issued on 9 November – urging president-elect Donald Trump to “strengthen scientific leadership” (an archived copy can be viewed here). The statement urged the incoming Trump administration to “incorporate the necessary policies that will enable our nation to reclaim its scientific leadership, which it has lost during the past decade”. Some APS members expressed concern about the tone of the release, which said that the “APS believes that such policies will help the Trump administration achieve its goal captured by its slogan, ‘Make America Great Again'”. The nature of these policies remains unclear. In September the APS reached out to both the Trump and Clinton campaigns with a series of five questions on topics of interest to the physics community. The society received responses only from the Clinton campaign. The now-retracted release also highlighted the fact that the US was ranked 10th worldwide in “overall innovation” by the Information Technology and Innovation foundation, mainly due to lack of funding for research. The Retraction Watch website, which reported on the statement the day it was withdrawn, has also published a round-up of the criticism levelled against the release by physicists on social media, as well as some support for the statement.

Three quantum physicists named to World Economic Forum computing council

Photograph of Andreas Wallraff
Quantum expert: Andreas Wallraff will serve on The Future of Computing Council of the World Economic Forum (Courtesy: P Rüegg/ETH Zürich)

Three quantum computing experts have been named to The Future of Computing council of the World Economic Forum. Vlatko Vedral of the University of Oxford, Andreas Wallraff of ETH Zürich and Jeremy O’Brien of the University of Bristol have joined the 19 person council. According to the World Economic Forum – which is a not-for-profit foundation – the council will sit for two years and “will explore how developments in computing could impact industry, governments and society in the future, and design innovative governance models that ensure that their benefits are maximized and the associated risks kept under control”.

 

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Mars mission gains currency in India, nuclear obliteration and a super-duper moon

The Reserve Bank of India's new Rs2000 banknote features the country's first interplanetary spacecraft, Mangalyaan (Courtesy: Ronnie Commissariat)
The Reserve Bank of India’s new Rs2000 banknote features the country’s first interplanetary spacecraft, Mangalyaan. (Courtesy: Ronnie Commissariat)

By Tushna Commissariat, James Dacey and Hamish Johnston

Nearly three years after it was successfully launched into orbit around Mars, India’s Mangalyaan orbiter has begun a new type of circulation – on a newly issued Indian banknote. Earlier this week, Indian prime minister Narendra Modi unexpectedly announced that the country’s ubiquitous Rs500 and Rs1000 notes would no longer be legal tender, effective immediately. New Rs500 and Rs2000 notes have instead be issued, the latter featuring the spacecraft.

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