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NASA to launch Cold Atom Lab in space

A laboratory for cooling an atomic gas to just a billionth of a degree above absolute zero will soon be sent up to the International Space Station (ISS) by physicists working at NASA’s Jet Propulsion Laboratory. The goal of the Cold Atom Lab (CAL) mission is to create long-lived Bose–Einstein condensates (BECs) that could lead to better sensors and atomic clocks for use on spacecraft. The BECs could even provide important insights into the nature of dark energy, according to the researchers.

First created in 1995, a BEC is made by trapping and cooling an atomic gas to an extremely low temperature so the atoms fall into the same low-energy quantum state. Instead of behaving like a collection of individual atoms, a BEC is essentially a large quantum object. This makes it very sensitive to disturbances such as stray magnetic fields and accelerations, and therefore BECs can be used to create extremely good sensors.

Falling down

Here on Earth, gravity puts an upper limit on the lifetime of a BEC – the atoms fall down and after a fraction of a second the BEC has dropped out of view of the experiment. In the microgravity environment of the ISS, however, NASA’s Robert Thompson and colleagues reckon that their BECs should be observable for 5–10 s. As well as allowing physicists to make more precise measurements of the quantum properties of BECs, the longer lifetime should also make the BECs better sensors. With further development, the team believes that BECs in space could endure for hundreds of seconds.

Five scientific teams will do experiments using Cold Atom Lab, including one led by Eric Cornell of the University of Colorado – who shared the 2001 Nobel Prize for Physics for creating the first BECs.

As well as creating BECs, CAL will also cool fermionic atoms to create degenerate Fermi gases. These systems can be made to mimic the behaviour of electrons in solids and could provide important insights into phenomena such as superconductivity. Physicists will also study ultracold mixtures of bosonic and fermionic atoms. Other planned experiments include atom interferometry and very precise measurements of gravity itself.

Pervasive forces

“Studying these hyper-cold atoms could reshape our understanding of matter and the fundamental nature of gravity,” says Thompson. “The experiments we’ll do with the Cold Atom Lab will give us insight into gravity and dark energy – some of the most pervasive forces in the universe.”

CAL will be contained within a package about the size of an “ice box”. This will contain a vacuum chamber, lasers and electronics. It will also include an electromagnetic “knife”, which will be used to cool the atoms. The lab is currently in the final stages of assembly and will be launched in August on a SpaceX CRS-12 rocket.

Flash Physics: Stellar heartbeat spotted, sensor detects oil spills, gluon contribution to proton spin

Nanosatellites measure massive stellar heartbeat

The world’s smallest astronomical satellites have identified the largest “stellar heartbeat” to date. Using the nanosatellite network Bright Target Explorer (BRITE)-Constellation mission, a group of astronomers has observed the pulse and tidal events of the Iota Orionis binary star system for the first time. The BRITE-Constellation project comprises five tiny satellites – cubes measuring 20 cm across – in low-Earth orbits. As the first-ever nanosatellite mission, they are used to investigate the structure and evolution of the brightest stars using high-precision photometry. One such system is Iota Orionis, which is the brightest star in the constellation Orion’s Sword and easily visible with the naked eye. Iota Orionis is dominated by a massive blue-giant star that is in a 29–day orbit with a main-sequence class B star. While light from the system is relatively stable 90% of the time, the team, led by Herbert Pablo of the University of Montreal observed a repetitive rapid dip and sharp spike. “The variations look strikingly similar to an electrocardiogram showing the sinus rhythms of the heart, and are known as heartbeat systems,” says Pablo, who is also a member of the Centre for Research in Astrophysics of Quebec (CRAQ). The phenomenon is caused by the stars coming closer together for a short time during their elliptical orbit. The closer contact means the gravitational forces between the stars become so strong that their shapes distort, their light is seen to pulse and quakes are triggered in the star. This the first time that a heartbeat and induced quakes have been observed in such a massive system (35 times the mass of the Sun). The findings, presented in the Monthly Notices of the Royal Astronomical Society, could provide new clues as to how massive stars evolve.

Floating spectrometer could detect oil spills

Photographs of the oil sensor
Spectrometer ahoy: the new sensor detects fluorescence from oil (left), allowing it to identify the type of oil. Components of the device are shown centre and right. (Courtesy: Óscar Sampedro / University of Vigo)

A floating sensor that can detect an oil spill in water and identify the type of oil present has been launched by Óscar Sampedro and José Salgueiro of the University of Vigo in Spain. The device uses the fact that crude or refined oil absorbs ultraviolet (UV) light and emits fluorescent light. Different types of oil emit different spectra of fluorescent light, and the type of oil can be determined by comparing the detected spectrum to a database of known oil types. While fluorescence is usually measured using delicate and expensive equipment, Sampedro and Salgueiro have built a low-cost and robust spectrometer based on four photodiode detectors. Each detector is covered by a cellophane film that filters out a different colour of light and the fluorescence is stimulated using UV light from inexpensive LEDs. “The four signals proved to be enough to build a specific fingerprint for every oil type used in our study, letting us identify the different types of oil,” explains Salgueiro. “This approach dramatically reduces the cost of the instrument and simplifies contamination testing.” The sensor also includes a low-cost microcontroller and a radio module that allows the device to send data and receive commands. The prototype sensor is about 30 cm in size and could be placed in a buoy. It is described in Applied Optics.

Gluons contribute 50% to proton spin

Half of the spin of the proton is associated with gluons, according to a state-of-the art calculation done by Yi-Bong Yang and Terrence Draper of the University of Kentucky and colleagues in the XQCD collaboration. Quantum chromodynamics (QCD) describes the proton as comprising three quarks that are bound together by gluons – bosons that mediate the strong force. Both quarks and gluons have intrinsic angular momentum – or spin – and physicists are keen to understand how these spins combine to give the proton its well-known spin of 1/2. Accelerator-based experiments done over the past three decades suggest that the quarks contribute about 30% of the spin, with the rest unaccounted for. As well as coming from the gluons, some of the remaining spin could be orbital angular momentum. There are also other effects that could screen the quark contribution or make some of it invisible to experiments. Calculating proton spin is extremely difficult because of the enormous strength of the strong nuclear force and the fact that calculations must consider large numbers of virtual quark–antiquark pairs that pop into and out of existence. The XQCD team is the first to use the computational technique lattice chromodynamics (QCD) to calculate the contributions of the gluons to the proton’s spin, which the researchers found to be about 50%. The calculations also suggest that screening of the quark spin is not significant, which means that the remaining 20% of the proton’s spin is probably related to orbital angular momentum and a topological effect that makes some of the quark spin invisible. The calculations are described in Physical Review Letters.

 

  • 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 plan to put ultracold atoms into space.

Organic semiconductor could reverse degenerative blindness

An organic retinal implant designed in Italy can stimulate retinal neurons and send signals to the brain, restoring near-normal vision indefinitely to rats with degenerative blindness without causing apparent damage to the rats’ eyes. That’s the claim of the researchers who developed it, who believe it could potentially lead to treatments for a major cause of blindness in humans. Other researchers, however, are more cautious.

Retinitis pigmentosa describes multiple genetic disorders that cause the photoreceptors on the retina to die. These lead to blindness, even though the other neurons concerned with signal processing and the optic nerve remain functional. There is currently no effective clinical treatment for the condition, but several groups are developing various proposals to effectively replace these lost photoreceptors by stimulating the retinal neurons artificially. While this could one day restore a patient’s vision, these approaches face severe difficulties. For example, most of the implants require a power supply, and wiring into the eyeball is extremely tricky. One solution is a photovoltaic cell that generates a voltage using only the incoming light, but this faces two principal problems. First, previous researchers have found the intensity of ambient light insufficient to stimulate the neurons. Secondly, silicon is much stiffer than nervous tissue: “In the long term, [silicon] can induce a reaction by the tissue,” says neuroscientist Fabio Benfenati of the Center for Synaptic Neuroscience and Technology in Genoa, “leading to encapsulation, [scarring] and things like that.”

Silken substrate

In the new research, materials scientist Guglielmo Lanzani of the Center for Nano Science and Technology in Milan and colleagues designed a more flexible, organic retinal implant based on a polymer solar cell. They deposited a thin layer of conductive polymer onto a silk-based substrate and covered it with a semiconducting polymer. When the semiconductor absorbs a photon, it creates an electron–hole pair called an exciton. The positive holes are drawn into the conducting polymer, whereas the electrons remain in the semiconductor, causing a negative charge.

Surgeons led by ophthalmologist Grazia Pertile of Sacro Cuore Hospital near Verona implanted the devices underneath the retinas of Royal College of Surgeons (RCS) rats – a strain of rats that reliably develop retinitis pigmentosa owing to a genetic mutation also found in some human cases of the disease. They placed the implants such that the semiconducting polymer was in contact with the retinal neurons, so absorption of light would apply a negative voltage to the cells. After 30 days, when the swelling from the surgery had completely subsided, Benfenati’s group compared the rats’ vision with both untreated RCS rats and healthy rats.

They first tested the pupil’s contraction in response to light, finding that although it was significantly impaired in untreated RCS rats, it was near normal in rats with the implant. In further tests using an electrode in the primary visual cortex, the researchers showed that implanted rats’ light sensitivity and visual acuity was substantially better than that of untreated RCS rats, and positron emission tomography showed that the metabolism of their primary visual cortices was higher. Furthermore, the rats – which naturally prefer dark environments – avoided light more effectively.

No ageing

The researchers tested the rats again later, both after 180 days and after 300 days: they found that, although the quality of the implanted rats’ vision declined, it stayed just as good relative to the other rats. “There is a generalized decrease in [the rats’] sight with age,” explains Benfenati. The recovery of the rats’ vision appears greater than can be explained by simple photovoltaics, so the researchers suspect other effects are involved, although precisely what these are remains unclear.

After dissecting the rats, the researchers tested prostheses removed from their eyes and showed that they worked similarly to prostheses stored in sterile conditions. The researchers are now testing an adapted implant in pig’s eyes: “We believe, based on these data, we could probably attempt the first [human] implant…within the next two years,” says Benfenati.

“The article is indeed interesting,” says ophthalmologist Mark Humayun of the University of Southern California in Los Angeles. He is impressed by the simplicity of using light to stimulate the implant, although he cautions: “The RCS rat retina is known to be much easier to stimulate. When it comes to a patient with longstanding retinal degeneration, we have found that ambient light intensity is insufficient and it requires intensified light – often multiple Suns.”

Bright lights

Daniel Palanker of Stanford University, is more sceptical, noting that “their RCS rats responded to every visual test, indicating that they still have photoreceptors”. He also pointed out that sub-retinal surgery is known to help preserve photoreceptors in RCS rats, and therefore these rats have better vision. He noted that, in their test of the implant, the researchers used light six million times more intense than the light levels to which the rats responded. “This indicates that the visual response has nothing to do with the photovoltaic response of the polymer,” he concludes. The researchers attempt to rule out this explanation by showing that a silk implant without the photovoltaic coating does not work, but Palanker is unconvinced: “The difference between the photovoltaic polymer and the passive control could be due to electrochemical reactions, which might help preserve photoreceptors better,” he says. “I’m not sure, but given other major problems, it’s not the central issue here.”

The research is described in Nature Materials.

Tracking neutrinos in virtual reality

As recently reported on this website, the app can be used with virtual reality (VR) headsets, enabling users to observe particle tracks inside the detector and enjoy tutorials about the nature of neutrinos. It can be downloaded free of charge from the App Store and Google Play.

Developed by an international team of physicists, the app also has a game element whereby users can search for neutrino signals. In the podcast, Glester asks the developers why they believe it is important for professional physicists to develop outreach tools such as VENu to inspire public interest in their work. Not one to rest on his laurels, the app’s chief developer Marco Del Tutto is already considering ways in which the group can further develop the app. Eventually, such an app could even be used as a citizen science tool in which the public can help particle physicists to identify neutrino detections amid large data sets.

As Glester mentions in the podcast, VENu is not the only immersive video experience that might be of interest to physicists. CMS-cardboard is a VR visualization of the CMS detector at CERN’s large hadron collider (LHC). Meanwhile, NASA has created a 360-degree artist’s impression of the surface of one of the seven planets recently discovered around the TRAPPIST-1 star.

Flash Physics: ESRF’s dinosaur eggs, coffee rings boost electronics, AAAS chief criticizes ban, cash for HERA

Synchrotron may help with giant-dinosaur mystery

Synchrotron X-ray analysis may provide the answer to how dinosaurs became giants. A collection of dinosaurs specimens, ranging from eggs to juveniles, has been analysed at the European Synchrotron Radiation Facility (ESRF) in France. It is the first time such a range of ages of the same species has been studied at ESRF and it could provide answers about dinosaur growth and evolution. Found in a reproductive colony in central Patagonia, the specimens analysed are prosauropod Mussaurus patagonicus – a primitive herbivorous dinosaur that lived 200 million years ago during the Late Triassic period. Prosauropods are believed to be ancestors of the giant sauropod dinosaurs common to the Jurassic period. However, how they evolved from intermediate-sized creatures to massive giants remains a mystery. Now, palaeontologist Diego Pol from the National Scientific and Technical Research Council (CONICET) in the Museum of Palaeontology Egidio Feruglio in Argentina hopes that high-resolution X-ray analysis will provide some answers. The study involves 30 eggs, a baby and a juvenile Mussaurus patagonicus. After being unable to achieve sufficient data in the home laboratory, Pol turned to Vincent Fernandez of ESRF. The synchrotron has been performing palaeontology studies for around a decade. By using high-energy X-ray radiation, 3D anatomical models can be built without the need to damage specimens. Furthermore, high-resolution investigation means it is possible to analyse the bone-growth patterns of the dinosaurs. While the data collected remain to be fully processed, it could provide key answers to Mussaurus patagonicus growth and the origin of giant dinosaurs.

Coffee-ring effect could make better solar cells

Microscope image showing a pattern of crystallites
Spilled semiconductor: researchers have discovered that crystallization behaviour can be controlled locally, creating regions with different crystal patterns. (Courtesy: KAUST)

A chance observation that a semiconductor solution behaves like spilled coffee could result in better electronic devices, according to researchers at the King Abdullah University of Science and Technology (KAUST) in Saudi Arabia. When coffee dries on a surface, the coffee solids are pushed towards the edge of the puddle to create a familiar coffee ring. This effect occurs in many liquids that contain tiny particles, and now Aram Amassian, Liyang Yu and colleagues have harnessed it to improve how thin-film semiconductors form when they are deposited in solution on a non-crystalline substrate. These semiconductors normally form polycrystalline films of tiny crystallites that are randomly oriented. While this is fine for some electronic devices, performance could be boosted by gaining more control over the crystal structure. Yu noticed that an organic semiconductor solution formed a coffee ring as it crystallized. Oddly, the thickest parts of the ring crystallized first, which is the opposite of what was expected. This led Yu to discover that the depth of the solution had an important effect on how the crystals were forming. Using this insight, the team used the local thickness of the semiconductor solution to create patterned semiconductor films in which the locations and orientations of crystallites can be controlled. “We can now make customized polycrystals on demand,” explains Amassian. The team hopes its discovery will lead to improvements in a wide range of devices including solar cells, and they describe the research in Science Advances.

AAAS’s Rush Holt responds to new Trump travel ban

Photograph of Rush Holt
Immigration concern: AAAS chief executive Rush Holt. (Courtesy: Chet Susslin / National Journal)

“We are concerned that the executive order announced 6 March may be implemented in a manner that will continue to restrict travel to the US and negatively impact students and scientists who seek to work and collaborate with their peers in the US,” says physicist Rush Holt, who is chief executive of the American Association for the Advancement of Science (AAAS). Holt was responding to a new executive order from US president Donald Trump that limits travel from six Muslim-majority countries in the Middle East and Africa. “Scientific progress depends on openness, transparency, and the free flow of ideas; these principles have helped the US attract and benefit from international scientific talent,” adds Holt. “Impacts to US leadership in science, technology and innovation should be considered in development of immigration and visa policy.”

Cash boost for South African radio telescope

The Hydrogen Epoch of Reionization Array (HERA) observatory, located in Losberg near Carnarvon in South Africa, has received $5.8m from the Gordon and Betty Moore Foundation in the US. The telescope array is currently under construction and consists of 35 14 m radio dishes. Last year, the US National Science Foundation announced it would invest $9.5m in HERA to boost the number of dishes to 240 by 2018. The new money from the Gordon and Betty Moore Foundation will increase that number even further to 350. The rise in the number of dishes will allow astronomers to explore the large-scale structures that formed during and prior to the epoch of reionization – a billion-year period after hydrogen collapsed into the first galaxies, a few hundred million years after the Big Bang. HERA is a precursor array to the upcoming Square Kilometre Array that will be built in southern Africa and Australasia in the coming decade.

 

  • 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 eye implant.

Meet the ‘angulon’, a new quasiparticle found in superfluid helium

The quasiparticle concept allows physicists to describe complex, many-body interactions in terms of the behaviour of a single particle-like entity. Usually these particles turn up in condensed-matter systems such as semiconductors, but a new type of quasiparticle known as an angulon has been proposed to describe the rotation of an atomic or molecular impurity within a solvent. First proposed theoretically two years ago, angulons have now been shown to explain the curious behaviour of a range of different molecules rotating within liquid helium.

Physicists have been studying quasiparticles since at least the 1940s, when Lev Landau and Solomon Pekar put forward the idea of the polaron to describe the behaviour of an electron travelling through a crystal lattice. As the electron moves forward it disturbs the surrounding atoms and so polarizes that region of the crystal. Describing the process completely would involve calculating the changing interaction between the electron and vast numbers of atoms, but Landau realized that it could be approximated by regarding the electron and the associated polarizations as a single particle that acts like a more massive electron travelling through free space.

In the latest work, Mikhail Lemeshko of the Institute of Science and Technology Austria just outside Vienna has looked at the collective motion of a rotating molecule interacting with the many atoms inside a drop of superfluid helium. Such drops allow scientists to hold single molecules at a fraction of a degree above absolute zero and record their spectra without distortions. In particular, it is useful for studying very reactive molecules such as free radicals.

Not enough atoms

The system can be analysed semi-classically by assuming that the trapped molecule creates a shell of non-superfluid helium around itself as it rotates, so slowing it down. But superfluid helium is a fundamentally quantum-mechanical material that is described by Bose–Einstein, as opposed to classical Boltzmann, statistics. Physicists have carried out brute-force numerical simulations of the system in recent years, but the complexity of the many-body interactions has limited the number of helium atoms in those simulations to around 100. The droplets used in experiments, in contrast, tend to contain more than 1000 atoms.

Lemeshko has found that he can simplify the problem enormously by using the concept of the angulon. Just as a polaron consists of an electron plus the deformations in the surrounding lattice, so an angulon is made up of the rotating molecule plus the disturbances it creates in the surrounding helium. And whereas a polaron is in effect a free-moving but more massive version of the electron, an angulon acts like an un-trapped version of the molecule in question but with a larger moment of inertia.

Having put forward the theory of angulons with Richard Schmidt of the Harvard-Smithsonian Center for Astrophysics in the US in 2015, Lemeshko has now compared that theory against 20 years of experimental results. For each of 25 different molecules, Lemeshko calculates the effect of the surrounding helium atoms on the molecule’s rotational constant – which is inversely proportional to its moment of inertia – and then compares the modified constant to the value obtained experimentally.

Two regimes

This was not a straightforward one-size-fits-all comparison, however. To obtain simple analytic expressions for molecular rotation, Lemeshko solved the angulon problem in two “regimes”. One regime, mainly applicable to heavy molecules such as those containing atoms of sulphur, involves molecules with significant coupling to the helium (a high potential energy) but with little kinetic energy. Conversely, the other regime, relevant to lighter molecules such as water, entails greater amounts of kinetic energy but weak coupling.

Although not all the predictions within the strong-coupling regime ended up within the experimental uncertainty, Lemeshko considers that for most heavy molecules he achieved “a good agreement with experiment”. He did even better in the weak-coupling regime, getting to within 2% of the experimental values for most light molecules. With some of the medium-sized molecules, however, he struggled, being unable to accurately predict their modified rotational constants within either the strong- or weak-coupling regimes. He says that an “intermediate-coupling” theory for angulons could in principle make accurate predictions here, but adds that rough estimates can be achieved in the meantime by splitting the difference between the strong- and weak-coupling predictions.

Despite the problems, Lemeshko concludes that the results of his study “provide strong evidence” that molecules rotating within superfluid helium do indeed form angulons. “An angulon is not a real physical entity in the sense that a fundamental particle such as an electron is,” he says. “But it is as real as any other quasiparticle.”

Electron angulons

Lemeshko is now looking to apply his theory beyond molecules within liquid helium. For example, he is investigating whether angulons could be used to represent electrons exchanging their orbital angular momentum with a crystal lattice. Doing so, he says, might aid the development of ultrafast switching and advanced data storage, but he cautions that this research is “very preliminary”.

The research is described in Physical Review Letters.

Flash Physics: Too radioactive even for robots, IBM to build 50 qubit computer, seeing through opaque materials

Fukushima too radioactive even for robots

Better robots are needed for investigating the Fukushima Daiichi nuclear plant after current designs failed due to radiation levels and debris obstacles. At a recent news conference, president of Fukushima Daiichi decommissioning, Naohiro Masuda, spoke about the need for more creative robot design after repeated failures. In 2011, multiple reactors at the Fukushima nuclear plant went into meltdown after a severe earthquake and tsunami. To safely decommission the damaged plant, its operator Tokyo Electric Power Company (TEPCO) must know exactly where the melted fuel is and the extent of structural damage to the surrounding buildings. The radiation levels, however, would kill a human within seconds, so TEPCO is reliant upon remote-controlled robotic probes. Yet early robots have come across unexpected challenges. In February, TEPCO sent in two robots to investigate the damaged reactor inside Unit 2 of the facility. The first was a cleaner robot designed to clear the way for the other “scorpion” robot that would assess damage and measure radiation and temperature. Unfortunately, the cleaning robot had to be withdrawn after only 2 hours of the planned 10 hour mission because the cameras began to malfunction due to high radiation levels. The scorpion-shaped robot then had to be abandoned before reaching its target location because it began to have difficulty moving and became stuck when crawling over rubble. It is unclear if this failure was due to debris or radiation levels. The Associated Press reports that Masuda called for more creative thinking when developing future robots. “We should think out of the box so we can examine the bottom of the core and how melted fuel debris spread out,” explains Masuda. The data collected and the robot failures imply that the clean-up and decommissioning of Fukushima will be more challenging than previously predicted. It is thought that the process will take decades to complete.

IBM to build 50 qubit quantum computers

Photograph of IBM researchers working on quantum technologies
Quantum development: IBM scientists Hanhee Paik (left) and Sarah Sheldon examine the hardware inside an open dilution fridge. (Courtesy: IBM)

IBM says it will build a new generation of universal quantum computers that will be available for commercial use via the IBM Cloud platform. The IBM Q systems will have about 50 quantum bits (qubits). This will make them 10 times larger than IBM’s five-bit quantum computer, which is already available on IBM Cloud and has attracted about 40,000 users. According to the US-based firm, increasing the number of qubits will be one step towards boosting the “quantum volume” – or computing power – of their quantum systems. Efforts will also focus on improving connectivity between qubits, boosting the reliability of quantum-logic operations and creating systems that are capable of highly parallel computations. The universal nature of the proposed computer should make it useful for solving a range of problems that are too complex for conventional computers. These include calculating the properties of molecules used to create new drugs and materials, finding optimal processes for supply chains and logistics and creating artificial intelligence systems. “To create knowledge from much greater depths of complexity, we need a quantum computer,” says Tom Rosamilia of IBM Systems. “We envision IBM Q systems working in concert with our portfolio of classical high-performance systems to address problems that are currently unsolvable, but hold tremendous untapped value.”

Very few photons needed to see through opaque material

An optical image of a region within a nearly opaque medium can be obtained using a surprisingly small number of photons. That is the conclusion of Mooseok Jang and Changhuei Yang at Caltech in the US and Ivo Vellekoop of the University of Twente in the Netherlands, who have shown that an established technique called optical phase conjugation (OPC) can be extended for use when very little light makes it out of the medium. OPC involves illuminating a point of interest in a nearly opaque medium with light beams from opposite directions. The first beam provides information about how light is scattered in the medium. This information is then used to cause the second beam to undergo the exact reverse scattering as it travels to the point of interest – illuminating that point. By scanning the beams around the sample, an image is built up. However, in very opaque materials scientists had thought that not enough light emerges to provide useful information about the scattering. Applying the technique to a sample of highly opaque opal, the trio showed that it worked when as few as 1000 photons were detected emerging from the sample – which is far fewer than the number of pixels in the detector used to measure the signal. The discovery is reported in Physical Review Letters and could be used to improve the optical imaging of opaque biological tissues such as brain matter.

 

  • 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 quasiparticle called the angulon.

Anger over Trump’s travel curbs

The scientific community has reacted with dismay at US President Donald Trump’s executive order to temporarily ban travellers from seven predominantly Islamic countries from entering the US. The concerns, which have been shared among academic institutions, hi-tech firms and scientific societies worldwide, remain even after a court of appeals upheld a federal judge’s decision to block the ban. As Physics World went to press, the Trump administration insisted that it will find a way to overturn those judgments and reinstate a ban similar – if not identical – to the original.

The executive order closed US entry to immigrants from Iran, Iraq, Libya, Somalia, Sudan and Yemen for 90 days, suspended the entry of refugees from anywhere in the world for 120 days and permanently banned Syrian citizens from entry. President Trump claimed that the order protected the country from incursion by “radical Islamic terrorists”. His opponents, meanwhile, assert that no individuals from the seven named nations have killed any Americans in terrorist attacks over the past four decades.

Issued a week after the new president’s inauguration, the ban prevented several scientists, doctors and members of technology companies from visiting or even returning to the US. Because the original executive order lacked detail, customs officers in some US airports initially refused entry to individuals from the targeted nations who possessed “green cards” that allow them to remain in the country with all the privileges of US citizens except the right to vote. “There really are science issues at stake, because you can’t do good science if you don’t have freedom of collaboration and a diversity of perspectives in research” says Rush Holt, the physicist and former Congressman who is chief executive of the American Association for the Advancement of Science (AAAS).

One prominent scientist to be affected by Trump’s ban is Iranian researcher Samira Asgari, who was initially prevented from flying to the US to take up a two-year contract at Harvard University to study the effect of the human genome on susceptibility to tuberculosis. She was later allowed to make the trip. Others simply decided not to fulfil their travel plans. Mohamed Hassan, a dual citizen of Sudan and Italy who is interim director of the World Academy of Sciences, cancelled a visit to the AAAS annual meeting in Boston last month. So did Sudanese electronic engineer Rania Abdelhameed Mokhtar, despite being scheduled to collect an award, which was given in absentia.

“The executive order signed by the US president is profoundly disruptive. It will immediately have a negative effect on scientific research and the essential scientific processes of exchanging information and ideas,” Hassan told Research Fortnight. “In the long run the order will erode trust in the US and undermine the sense that the US is a reliable partner for scientific research. This is very disturbing both for scientists from the developing world and for our colleagues in North America and Europe.”

Scientific societies outside the US have lamented the prevention of individuals from specific countries from entering the US. The International Astronomical Union (IAU) noted in a statement issued before the ban was temporarily overturned that it “considers that mobility restrictions can have a direct impact on the astronomical communities of countries at both ends of the ban, as well as astronomy as a whole”. IAU general secretary Piero Benvenuti told Physics World that the IAU will “always denounce the possible damage that such decisions may cause to science” adding that the IAU has no plans to stop activities in the US because of the ban. “If anything, we will try to facilitate the participation in our activities, scientific and educational, by any world citizen,” he adds. However, G2 Massive Stars, one of the IAU’s 35 commissions, which plan activates in various sub-fields of astronomy, announced in early February that it will not hold any meeting in the US while any such ban remained in place.

National scientific organizations have also added their concerns. A statement by a group of German scientific societies describes the order as “a sweeping discrimination of human beings based on their ethnicity and consequently also an act of aggression against the fundamental values of science”. And according to the UK’s Royal Astronomical Society, “The ban hinders researchers from sharing their work with their peers, a fundamental tenet of scientific endeavour. The restrictions threaten to damage collaboration between the US and nations around the world.”

Scientific progress depends on openness, transparency, and the free flow of ideas and people

Within the US, a group of 171 scientific, engineering and educational societies, national associations and universities – among them the American Physical Society and the American Institute of Physics – issued a statement before the ban was overturned urging the administration to rescind the order. The statement expresses deep concern that it will “have a negative impact on the ability of scientists and engineers in industry and academia” to travel freely.

“Scientific progress depends on openness, transparency, and the free flow of ideas and people, and these principles have helped the US attract and richly benefit from international scientific talent,” the statement says. “The executive order will discourage many of the best and brightest international students, scholars, engineers and scientists from studying and working, attending academic and scientific conferences, or seeking to build new businesses in the US. Implementation of this policy will compromise the United States’ ability to attract international scientific talent and maintain scientific and economic leadership.”

Slow out of the box

The travel ban is not the only issue that has concerned scientists as they come to terms with a new approach to business at the White House. As the Senate approved the administration’s nominees, government efforts to counter global warming appear all but certain to be reduced, although perhaps more slowly than some administration advocates have suggested. Scott Pruitt, the lawyer whom the senate approved as the new head of the Environmental Protection Agency (EPA) late last month, reportedly plans to cut the agency’s staff, close some of its regional offices, repeal recent regulations on battling climate change and weaken its regulations on environmental matters. Intriguingly, a predecessor of Pruitt’s, Anne Gorsuch, carried out a similar downsizing agenda as Ronald Reagan’s first EPA director in the early 1980s. The Trump administration has nominated her son, Neil Gorsuch, as a Supreme Court justice.

Rumours also emerged last month that the Princeton University physicist William Happer could become Trump’s scientific adviser. In the past Happer has said that researchers working on climate change resemble a “glassy-eyed chanting cult”, adding that climate change was a “so-called” science. The physicist apparently met Trump in January to discuss taking the role and has since said that if he was offered the job, he would accept. Another individual tipped as possible science adviser – computer scientist David Gelernter from Yale University – has said that he is “unconvinced” by evidence of human contribution to climate change. He has also criticized the “intellectualism” of modern academia.

The House of Representatives Science, Space and Technology Committee has also resumed efforts it began two years ago to restrict the ways in which government agencies use scientific results in their development of policies. Lamar Smith, the Texas Republican who heads the committee, has continued to question the findings of government scientists. In a recent hearing, Smith called on the AAAS publication Science Advances to retract a paper on “data biases in global warming” by National Oceanic and Atmospheric Administration (NOAA) researchers. He says that a former NOAA scientist had questioned the team’s scientific integrity. In testimony, Rush Holt stated that the objection was to the way the data was archived rather than the paper’s findings, which have been replicated. “Policy-makers should never dictate the conclusions of a scientific study and they should base policy on a review of relevant research and the provision of relevant statutes,” Holt told the committee. “In other words, the integrity of the process must be upheld.”

Trump is also likely to relax long-held policies on the process of approving new pharmaceutical drugs. The administration has raised the possibility of a presidential commission to study the safety of vaccines, including a purported connection between vaccines and autism that the medical profession has discredited. “What will become of the major government agencies of scientific research, the National Institutes of Health and the National Science Foundation?” asks Bard College president Leon Botstein in a comment in the New York Times. “Will their research agendas be manipulated to fit Trump’s view of reality? Will there be a continuing erosion of support for basic research as opposed to research that contributes to some commercial product?”

An open letter issued by 39 European science organizations warns against the executive order and also indications that the US government is paying too much attention to views not based on fact and sound scientific evidence, especially in areas such as climate science and the safety of vaccines. It also highlights the danger of the administration stopping scientists from speaking to the media without first seeking permission. “All of these are at odds with the principles of transparency, open communication, [and the] mobility of scholars and scientists, which are vital to scientific progress and to the benefit our societies, economies and cultures derive from it,” the statement says. “Restrictions on research, scientists and research centres in inconvenient areas have no place in science…Our colleagues working in the US will suffer, the United States and US citizens will pay a price, as will Europe and Europeans, and countries and people all across the globe.”

One US group has gone beyond just issuing statements. On 22 April thousands of scientists are expected to participate in a March for Science in Washington DC as well as in several other cities around the world. The event is intended to “champion publicly funded and publicly communicated science as a pillar of human freedom and prosperity”. While much of the scientific community approves of the event, some members worry that it could be counterproductive, by politicizing science. “[The march] will make my job more difficult and increase polarization,” Robert Young, a Western Carolina University geologist who studies the effect of rising sea levels on coastlines, wrote in the New York Times.

Holt, meanwhile, says that the US scientific community is anxious that science will suffer from government neglect. “The administration and transition team have been silent about scientific issues. Many scientists think that it’s been an ominous silence,” he says. “There is no science adviser appointed and essentially no new appointments of trained scientists and engineers to any positions. If this is to be a science-friendly administration they’re pretty slow out of the box.”

Exoplanet christening, physics on the catwalk, ultrasonic wine

Whiskey aging barrels
Quick spirit: ultrasonic waves speed up the ageing process. (CC BY-SA 3.0 Bbadgett)

By Sarah Tesh

Last week NASA announced the major find of seven Earth-like exoplanets orbiting a nearby dwarf star. The news that at least three of the seven could possibly support life was reported far and wide. Yet, as with most astronomical finds, the planets do not have the most imaginative names. Simply named after the star they orbit, they are currently called TRAPPIST-1a to TRAPPIST-1h. So NASA took to Twitter with the request #7NamesFor7NewPlanets and the public delivered. Suggestions have included the names of lost astronauts, famous composers and ancient deities. But naturally, there were also some less sensible contributions, including the seven dwarfs, many Harry Potter references, dedications to Pluto and, obviously, Planet McPlanetface 1 to 7.

(more…)

Complex ultrasound signals created by light

A new way of creating specially shaped pulses of ultrasound using light and a 3D printer has been unveiled by Michael Brown and colleagues at University College London. The pulses, which are creating using the photoacoustic effect in a 3D-printed material, could be tailored to perform a range of tasks including manipulating biological cells and delivering drugs to specific parts of the body.

Renowned for its ability to let us see inside the body, ultrasound refers to acoustic waves at frequencies above about 20 kHz. Such waves can also be used for medical treatment, industrial product imaging and chemistry. Researchers have also recently developed acoustic tractor beams and tweezers for the non-contact manipulation of small objects.

Ultrasound is usually generated by applying an electrical signal to a piezoelectric transducer. Complicated ultrasound signals can be created using arrays of transducers, but the ability to create certain very precise waveforms would require many tiny components – making such ultrasound generators expensive.

Heating up

Brown and colleagues’ technique to create specific ultrasound waveforms involves using a light signal, such as a laser pulse, to heat part of an object so it locally expands. This triggers vibrations that travel out from the surface of the material as sound waves. The precise nature of the ultrasound wave is defined by the 3D shape of the surface of the photoacoustic material.

To create surfaces that output specific ultrasound signals, the team developed an algorithm that calculates the 3D surface profile required to create a desired ultrasound signal. “Our algorithm allows for precise control of the intensity of sound at different locations and the time at which the sound arrives, making it quick and easy to design surfaces or ‘lenses’ for a desired application,” says Brown.

At the heart of their ultrasound generator is a 3D-printed cylinder of transparent material. One end of the cylinder is flat, while the other has a 3D pattern picked specifically to create an ultrasound wave in the shape of the numeral “7” (see figure). The patterned surface is then coated with black plaint, which makes it a good absorber of light.

To create an ultrasound pulse, a laser pulse is fired at the flat end of the cylinder. The light travels through the cylinder and strikes the paint at the opposite end, where ultrasound waves are emitted from the surface of the cylinder into a tank of water containing an ultrasound detector.

Using this set-up, Brown and colleagues were able to create and detect ultrasound waves shaped like a “7”. But as well as creating pulses with complicated shapes, the technique could also be used to create intense ultrasound pulses. “One useful feature of the photoacoustic effect is that the initial shape of the sound that’s generated is determined by where the light is absorbed,” explains Brown. “This can be used to create tightly focused intense points of sound just by depositing an optical absorber on a concave surface, which acts like a lens.”

Tiny bubbles

One possible application of the ultrasound generator is to create acoustic tweezers that can manipulate living cells and other delicate objects without any physical contact. Another possible use, according to Brown, is the targeted delivery of drugs. This would involve encapsulating the drugs in tiny bubbles that burst only when exposed to an ultrasound signal at, say, the site of a tumour.

The technique could also be used to correct for distortions to ultrasound signals as they travel through tissue or other materials. If the structure of the material is known beforehand, an ultrasound generator that compensates for the distortions can be made. So far, limitations in laser power have restricted the team to using pulsed lasers, but Brown says that the team is also interested in generating ultrasound using continuous-wave optical signals.

The new technique is described in Applied Physics Letters.

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