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Ultrasound creates 2D arrays of droplets

Liquid droplets have been arranged into 2D arrays by researchers at the University of Bristol in the UK. The droplets contain entangled polymers and are created within a tank of water. A range of different chemicals can be added to the droplets, which could be used to create high-throughput analyses systems for developing new drugs or performing rapid medical diagnostics. The droplet arrays could even be used to study how living cells communicate with each other.

Although arrays of liquid droplets have been made before, previous attempts had involved either using oil-and-water mixtures or evaporating the liquid to create the array on a dry surface. Neither technique is also suitable for supporting water-based chemical reactions, which was a primary goal of Bruce Drinkwater and his team of physicists, engineers and chemists, who developed the new technology.

Coacervation and coalescence

The droplet-forming process begins with an aqueous solution of the polymer PDDA and the biomolecule adenosine triphosphate (ATP). Electrostatic interactions cause these two materials to agglomerate into tiny nanometre-sized droplets by a process of “coacervation”. When a 2D ultrasound standing wave is created in the liquid using piezoelectric transducers, the droplets move to the nodes of the standing wave, where they coalesce and grow until they reach about 50–100 μm in diameter.

The uniformity of the droplets is amazing
Bruce Drinkwater, University of Bristol

The result is a square lattice of identical droplets (see image above). “The uniformity of the droplets is amazing,” says Drinkwater. “I’m convinced this technology will have many applications in the next generation of lab-on-a-chip applications.”

By adjusting the ultrasound signals, the team was able to transform a column of droplets into a solid line of PDDA/ATP and then back again into a column of droplets. The researchers could control the size of the droplets and the spacing between them. They also showed that it is possible to load the droplets with a wide range of substances including proteins, enzymes, DNA and even micron-sized solid particles.

Localized chemistry

In one set of experiments, the team introduced a dye to one side of the tank and watched as the chemical diffuses across the array to create a concentration gradient. Such experiments could be used, for example, to study the effects of different concentrations of a chemical on the contents of the droplets. The team also showed that when several different additives were introduced to different locations of the array, the substances tended to remain localized within a region of droplets. This could be used to create arrays in which different droplets contain different chemicals.

Drinkwater told physicsworld.com that the team is now looking at how to create 3D lattices of droplets using ultrasound. He also says that it is working on making the ultrasonic components of the system more robust to the chemicals used – something that must be done before the system can be commercialized. The team is also looking at how arrays of droplets could be used to simulate how living cells communicate to each other using chemicals. This would involve making the droplets more complicated by creating structures that are analogues to those found in living cells.

The research is described in Nature Communications.

  • Hamish Johnston spoke to Bruce Drinkwater about the physics of ultrasound. You can listen to that conversations and watch a video of an acoustic “tractor beam” here.

Flash Physics: Strong summer ice, spying the nearest exoplanet and École Polytechnique degrees in English

Summer ice is stronger, say scientists

Sea-ice structures called “ice ridges” become stronger as the summer progresses, thanks to an influx of less salty water. That’s the conclusion of physicist Aleksey Shestov and colleagues at the University Centre in Svalbard, Norway, who have studied the ridges that form in the Arctic Ocean when ice floes slam together. These ridges extend both above and below the surrounding flat ice. The submerged portion of the ridge is a jumble of ice chunks with pockets of salty water that tend to form in the summer. These water pockets should weaken the ice ridge, but Shestov’s team has discovered that less-salty melt water that pools on the surface of the ice trickles down into the pockets and reduces the salinity of the water in the pockets. Water that contains less salt freezes at a higher temperature than sea water, and this allows the pockets to solidify and strengthen the ridge. “The ice ridge actually consolidates during the summer,” explains Shestov. “It’s still melting, but there is also freezing inside the ridge.” The research could inform how the hulls of ships and other marine structures are designed to withstand ice damage.

Project Blue plans to image our nearest exoplanet neighbour

Proxima Centauri as seen by the Hubble Space Telescope
Nearest neighbour: Project Blue could soon be focusing on Proxima Centauri – shown here as seen by the Hubble Space Telescope. (Courtesy: ESA/Hubble)

A privately led, non-profit effort known as “Project Blue” plans on taking the first image of our nearest exoplanet neighbour – the recently discovered terrestrial planet that orbits Proxima Centauri, the closest star to Earth. The planet’s existence was confirmed this August and it lies within its star’s habitable zone. This means that the planet could sustain liquid water on its surface, and may even have an atmosphere. Project Blue aims at launching a state-of-the-art exoplanet-imaging telescope into space by 2019 and operating it until 2022. The project takes its name from the celebrated “Pale blue dot” image of Earth taken by the Voyager spacecraft in 1980. It is led by the BoldlyGo Institute, Mission Centaur, the SETI Institute and the University of Massachusetts Lowell. The mission is estimated to cost less than $50m.

French university launches degrees in English

Photograph of international students of the Ecole Polytechnique
International flavour: students of the École Polytechnique. (Courtesy: École Polytechnique/Jérémy Barande

One of France’s most prestigious universities – École Polytechnique – is to offer five new graduate degrees that will be taught exclusively in English. The courses, which begin this academic term, break away from traditionally being taught in French and are in energy environment, corporate strategy, metroeconomics, big data for business and “digitized society”. The institution is also launching a new Bachelor degree in mathematics – also taught exclusively in English – that will start in 2017 with applications opening in November. Students on the course, which will be École Polytechnique’s first undergraduate programme, will specialize in mathematics but will also study either computer science, physics or economics.

 

  • 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 ultrasonic droplets.

What could you do with a 50- or 100-qubit quantum computer?

Computers based on quantum processes have the potential to be exponentially more powerful than today’s computers. The processing in classical computing is based on combinations of “bits” that can be in one of two states (0 or 1). In quantum computing the processing is based on quantum bits – or “qubits” – that can be in a superposition of different states at the same time. Creating and sustaining qubits in the real world, however, presents many significant engineering challenges on account of the fragile nature of these systems. The exciting question is of course: what can we do with these machines once we start to create practical quantum computers based on multiple-qubit systems?

In this video, Andrea Morello from the University of New South Wales in Australia addresses this question. Among other possible applications he discusses the idea of using quantum computers to test the very foundations of the theory of quantum mechanics. This video is part of our 100 Second Science series, in which researchers give concise presentations covering the spectrum of physics.

Transforming African astronomy with MeerKAT

Nithaya Chetty
Looking ahead Nithaya Chetty. (Courtesy: National Research Foundation)

What is the Square Kilometre Array (SKA)?

The SKA will be the world’s largest radio telescope when it comes online in the coming decade. It will consist of thousands of dishes and antennas spread out across Africa and Australasia. The first phase of the SKA, which will be complete around 2023, will see an array of almost 200 dishes built in South Africa covering the bulk of the high- and mid-frequencies of the radio spectrum, while Australia will host over 100,000 low-frequency dipole antennas. The second phase will complete the arrays at both sites and when finished by 2030 the SKA will consist of several thousand high-frequency and mid-frequency telescopes and aperture arrays, along with several million low-frequency antennas.

What is South Africa’s contribution?

South Africa is currently building MeerKAT – a 64-dish mid-frequency array that is located in the Karoo semi-desert region more than 500 km north-east of Cape Town. It is managed by the National Research Foundation (NRF) and when fully operational by the end of 2017 it will be the most sensitive radio telescope of its kind in the world. An additional 133 dishes will be built by the international SKA consortium in South Africa and we will integrate our 64 dishes into the broader array in 2023.

Who is paying for MeerKAT?

MeerKAT is being funded by the South African Department of Science and Technology. South African science minister Naledi Pandor has been instrumental in getting the project off the ground.

What is its current status?

We now have more than 25 dishes bedded down and are beginning to produce scientific results.

We will be discovering objects and studying scientific, astronomical phenomena that we might not have predicted and could not have imagined

Has the telescope made any scientific discoveries yet?

Using just 16 dishes, in June we discovered several hundred new galaxies. So by the time we get to the fully fledged SKA we will be discovering objects and studying scientific, astronomical phenomena that we might not have predicted and could not have imagined. It will be transformational science because the instrument will be so much bigger and more powerful that anything we currently have.

What is the timeline for the rest of the SKA construction?

The various partner governments are still in the process of securing the treaty organization, hosting agreement, funding, procurement and so on. It is still a work in progress and until we have all the partners fully on board I cannot say for sure when the first phase of the SKA will roll out and be fully functional, but this is planned for around 2023. If there is a delay, the NRF will continue to operate MeerKAT as a South African telescope.

How much of South Africa’s science funding is being spent on the SKA?

Funding for science and research infrastructure in South Africa comes primarily from the NRF with an annual budget of ZAR 4bn ($300m). Cash for astronomy, not including the SKA, is about 4.5% of this amount. With money for the SKA included, it is around 27%, with funding being a special allocation from the National Treasury. Once we have finished construction of MeerKAT the operational budget will be around 8% per year of the total capital expenditure.

How are you engaging other African countries?

When we led the site-host bid we involved eight other African partner countries: Botswana, Ghana, Kenya, Madagascar, Mauritius, Mozambique, Namibia and Zambia. SKA instruments will only be built in these countries in the second phase of the SKA, which will begin in 2023. We have begun development in our African partner countries by refurbishing unused telecommunications dishes for single-dish radio astronomy and to start work on an African very-long-baseline interferometry network.

How are you training people for the SKA?

We are very keen to develop our own home-grown talent, and we have put in a huge effort to achieve that for more than a decade now. The annual ZAR 50m SKA human capacity development programme has issued more than 800 grants in the last decade, including for degree-level students and research chairs for established individuals. We have managed to recruit high-profile scientists from around the world to increase our research student supervisory capacity.

How will you define success for the SKA project?

From a South African perspective, it would have to be leading transformational science using the SKA. But of course it goes beyond doing science. I would like to see the SKA project attracting a new generation of children to science, and also stimulating innovation and supporting industry. For a project on this scale you can imagine that the technical innovations – for example in “big data” – are at the cutting edge. We would like those innovations to be done by South African industries so there is potential for commercialization of those technologies.

‘Radical’ new microscope lens combines high resolution with large field of view

A new microscope lens that offers the unique combination of a large field of view with high resolution has been created by researchers in the UK. The new “mesolens” for confocal microscopes can create 3D images of much larger biological samples than was previously possible – while providing detail at the sub-cellular level. According to the researchers, the ability to view whole specimens in a single image could assist in the study of many biological processes and ensure that important details are not overlooked.

Laser-scanning confocal microscopes are an important tool in modern biological sciences. They emerged in the 1980s as an improvement on fluorescence microscopes, which view specimens that have been dyed with a substance that emits light when illuminated. Standard fluorescence microscopes are not ideal because they pick up fluorescence from behind the focal point, creating images with blurry backgrounds. To eliminate the out-of-focus background, confocal microscopes use a small spot of illuminating laser light and a tiny aperture so that only light close to the focal plane is collected. The laser is scanned across the specimen and many images are taken to create the full picture. Due to the small depth of focus, confocal microscopes are also able to focus a few micrometres through samples to build up a 3D image.

In microscopy there is a trade-off between resolution and the size of the specimen that can be imaged, or field-of-view – you either have a large field-of-view and low resolution or a small field-of-view and high resolution. Current confocal microscopes struggle to image large specimens, because low magnification produces poor resolution.

Stitched together

“Normally, when a large object is imaged with a low-magnification lens, rays of light are collected from only a small range of angles (i.e. the lens has a low numerical aperture),” explains Gail McConnell from the Centre for Biophotonics at the University of Strathclyde, in Glasgow. “This reduces the resolution of the image and has an even more serious effect in increasing the depth of focus, so all the cells in a tissue specimen are superimposed and you cannot see them individually.” Large objects can be imaged by stitching smaller images together. But variations in illumination and focus affect the quality of the final image.

McConnell and colleagues set out to design a lens that could image larger samples, while retaining the detail produced by confocal microscopy. They focused on creating a lens that could be used to image an entire 12.5 day-old mouse embryo – a specimen that is typically about 5 mm across. This was to “facilitate the recognition of developmental abnormalities” in such embryos, which “are routinely used to screen human genes that are suspected of involvement in disease”, says McConnell.

Dubbed a mesolens, their optical system is more than half a metre long and contains 15 optical elements. This is unlike most confocal lenses, which are only a few centimetres in length. The mesolens has a magnification of 4× and a numerical aperture of 0.47, which is a significant improvement over the 0.1–0.2 apertures currently available. The system is also able to obtain 3D images of objects 6 mm wide and long, and 3 mm thick.

The high numerical aperture also provides a very good depth resolution. “This makes it possible to focus through tissue and see a completely different set of sub-cellular structures in focus every 1/500th of a millimetre through a depth of 3 mm,” explains McConnell. The distortion of the images is less than 0.7% at the periphery of the field and the lens works across the full visible spectrum of light, enabling imaging with multiple fluorescent labels.

Engineering and design

The lens was made possible through a combination of skilled engineering and optical design, and the use of components with very small aberrations. “Making the new lens is very expensive and difficult: to achieve the required very low field curvature across the full 6 mm field of view and because we need chromatic correction through the entire visible spectrum, the lens fabrication and mounting must be unusually accurate and the glass must be selected very carefully and tested before use,” explains McConnell.

The researchers used the lens in a customized confocal microscope to image 12.5 day-old mouse embryos. They were able to image single cells, heart muscle fibres and sub-cellular details, not just near the surface of the sample but throughout the depth of the embryo. Writing in the journal eLife, the researchers claim “no existing microscope can show all of these features simultaneously in an intact mouse embryo in a single image.”

The researchers also write that their mesolens “represents the most radical change in microscope objective design for over a century” and “has the potential to transform optical microscopy through the acquisition of sub-cellular resolution 3D data sets from large tissue specimens”.

Rafael Yuste, a neuroscientist at Columbia University in New York, saw an earlier prototype of the mesolens microscope. He told physicsworld.com that McConnell and colleagues “have completely redesigned the objective lens to achieve an impressive performance”. He adds that it could enable “wide-field imaging of neuronal circuits and tissues while preserving single-cell resolution”, which could help produce a dynamic picture of how cells and neural circuits in the brain interact.

Video images taken by the mesolens can be viewed in the eLife paper describing the microscope.

Flash Physics: Opportunity Rover goes crater diving, new deputy director of US Department of Energy, underwater transistors

NASA’s Opportunity Rover to drive into crater and explore Mars gully

NASA’s Opportunity Mars Rover, which began yet another extended mission this month, will visit the interior of a crater on Mars and drive down an ancient gully carved out by a fluid (that may have been water) – a first for a Mars rover. Opportunity, which is the longest active rover on Mars, launched on 7 July 2003 and landed on Mars on 24 January 2004, on a planned mission of 90 Martian days, which is equivalent to 92.4 Earth days. “We have now exceeded the prime-mission duration by a factor of 50,” notes John Callas, Opportunity’s project manager. “Milestones like this are reminders of the historic achievements made possible by the dedicated people entrusted to build and operate this national asset for exploring Mars.” Opportunity began its latest extended mission in a part of the western rim of Endeavour Crater – the rover reached the edge of this crater in 2011 after more than seven years of investigating a series of smaller craters. The gully chosen as the next major destination slices west-to-east through the rim about half a kilometre south of the rover’s current location. The Opportunity team will drive the rover down the full length of the gully, onto the crater floor. The second goal of the extended mission is to compare rocks inside Endeavour Crater with the dominant type of rock Opportunity examined on the plains that it explored en route to the current spot.

Steve Binkley takes over as DOE deputy director as Patricia Dehmer retires

Steve Binkley has been appointed as the US Department of Energy’s deputy director for science as of this November, as the current director Patricia Dehmer will retire on 10 November. Binkley – who is currently head of the department’s Advanced Scientific Computing Research programme – will oversee six different research programmes including high-energy physics, nuclear physics, fusion-energy sciences and more, as well as evaluating existing and proposed new facilities. Dehmer has had a long and distinguished career at the department and during her time as the director of the DOE’s Office of Basic Energy Sciences she oversaw a doubling of the programme’s budget and $3bn in major construction projects, including the Spallation Neutron Source, the Linac Coherent Light Source, and the National Synchrotron Light Source II.

N-type electrochemical transistor works underwater

Schematic of the new n-type organic electrochemical transistor
Water proof: schematic of the new n-type organic electrochemical transistor showing the gold electrodes (yellow), parylene C (grey) and the neat polymer red. (Courtesy: Alexander Giovannitti/Nature Communications)

An n-type organic electrochemical transistor (OECT) that works underwater has been created by an international team of researchers. OECTs show great promise as biological sensors because they can convert ionic signals in liquid media into electronic signals. One challenge facing the development of practical sensing devices is that OECTs have been limited to being “p-type” devices based on electrical conduction by holes. If OECTs could also be based on n-type devices that use electrons to conduct electricity, then better and more versatile sensors could be created. The problem, however, is that n-type materials tend to be unstable in water. Now Alexander Giovannitti of Imperial College London and colleagues have created OECTs from a new semiconductor polymer that supports both n- and p-type conduction and is also stable in water. Giovannitti said that the new OECTs “might be able to detect abnormalities in sodium and potassium ion concentrations in the brain, responsible for neuron diseases such as epilepsy”. The OECTs are described in Nature Communications.

 

  • 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 high-resolution lens for microscopes.

The 2016 Physics World Focus on Neutron Science is out now

By Michael Banks

pwneut16cover-200Neutron scientists in Europe are facing a number of headwinds in the coming decade. One is the uncertainty caused by the recent UK vote to leave the European Union. Another is the impending closure of ageing reactors across the continent such as the Orphée reactor in Paris and the BER II reactor in Berlin, which could both shut down by 2020.

A recent report by an expert group of researchers – the Neutron Landscape Group – paints a worrying challenge for neutron scientists. It forecasts that the continent’s supply of neutrons could drop by as much as a half over the next decade – a shortfall in capacity that is unlikely to be met by the upcoming European Spallation Source in Lund, Sweden.

That said, there are plans to help overcome the impending neutron gap, including proposals to plug it by building compact, specialist sources. Improvements to accelerator technology and instruments could also help by boosting the number of usable neutrons. Scientists at the US Spallation Neutron Source, for example, are pioneering a method to improve its proton beam energy using plasma processing, while the National Institute of Standards and Technology’s world-leading neutron microscope will soon open up to users.

(more…)

The physics of Luke Cage’s skin, meet the 'mathekniticians', lessons from the only girl in a physics class

By Hamish Johnston

Marvel’s Luke Cage is a superhero television series that has just debuted on Netflix. Cage’s superpower is that his skin is impervious to bullets and other projectiles fired at him by villains. But could it be possible to create a skin-like layer that would allow someone to emerge unscathed from machine gun fire? The Nerdist’s Kyle Hill has the answer in the above video.

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Correlation between galaxy rotation and visible matter puzzles astronomers

A new study of the rotational velocities of stars in galaxies has revealed a strong correlation between the motion of the stars and the amount of visible mass in the galaxies. This result comes as a surprise because it is not predicted by conventional models of dark matter.

Stars on the outskirts of rotating galaxies orbit just as fast as those nearer the centre. This appears to be in violation of Newton’s laws, which predict that these outer stars would be flung away from their galaxies. The extra gravitational glue provided by dark matter is the conventional explanation for why these galaxies stay together. Today, our most cherished models of galaxy formation and cosmology rely entirely on the presence of dark matter, even though the substance has never been detected directly.

These new findings, from Stacy McGaugh and Federico Lelli of Case Western Reserve University, and James Schombert of the University of Oregon, threaten to shake things up. They measured the gravitational acceleration of stars in 153 galaxies with varying sizes, rotations and brightness, and found that the measured accelerations can be expressed as a relatively simple function of the visible matter within the galaxies. Such a correlation does not emerge from conventional dark-matter models.

Mass and light

This correlation relies strongly on the calculation of the mass-to-light ratio of the galaxies, from which the distribution of their visible mass and gravity is then determined. McGaugh attempted this measurement in 2002 using visible light data. However, these results were skewed by hot, massive stars that are millions of times more luminous than the Sun. This latest study is based on near-infrared data from the Spitzer Space Telescope. Since near-infrared light is emitted by the more common low-mass stars and red giants, it is a more accurate tracer for the overall stellar mass of a galaxy. Meanwhile, the mass of neutral hydrogen gas in the galaxies was provided by 21 cm radio-wavelength observations.

McGaugh told physicsworld.com that the team was “amazed by what we saw when Federico Lelli plotted the data.”

The result is confounding because galaxies are supposedly ensconced within dense haloes of dark matter. Furthermore, the team found a systematic deviation from Newtonian predictions, implying that there is some other force is at work beyond simple Newtonian gravity.

It’s an impressive demonstration of something, but I don’t know what that something is
James Binney, University of Oxford

“It’s an impressive demonstration of something, but I don’t know what that something is,” admits James Binney, a theoretical physicist at the University of Oxford, who was not involved in the study.

This systematic deviation from Newtonian mechanics was predicted more than 30 years ago by an alternate theory of gravity known as modified Newtonian dynamics (MOND). According to MOND’s inventor, Mordehai Milgrom of the Weizmann Institute in Israel, dark matter does not exist, and instead its effects can be explained by modifying how Newton’s laws of gravity operate over large distances.

“This was predicted in the very first MOND paper of 1983,” says Milgrom. “The MOND prediction is exactly what McGaugh has found, to a tee.”

However, Milgrom is unhappy that McGaugh hasn’t outright attributed his results to MOND, and suggests that there’s nothing intrinsically new in this latest study. “The data here are much better, which is very important, but this is really the only conceptual novelty in the paper,” says Milgrom.

No tweaking required

McGaugh disagrees with Milgrom’s assessment, saying that previous results had incorporated assumptions that tweak the data to get the desired result for MOND, whereas this time the mass-to-light ratio is accurate enough that no tweaking is required.

Furthermore, McGaugh says he is “trying to be open-minded”, by pointing out that exotic forms of dark matter like superfluid dark matter or even complex galactic dynamics could be consistent with the data. However, he also feels that there is implicit bias against MOND among members of the astronomical community.

“I have experienced time and again people dismissing the data because they think MOND is wrong, so I am very consciously drawing a red line between the theory and the data.”

Much of our current understanding of cosmology relies on cold dark matter, so could the result threaten our models of galaxy formation and large-scale structure in the universe? McGaugh thinks it could, but not everyone agrees.

Way too complex

Binney points out that dark-matter simulations struggle on the scale of individual galaxies because “the physics of galaxy formation is way too complex to compute properly,” he says, the implication being that it is currently impossible to say whether dark matter can explain these results or not. “It’s unfortunately beyond the powers of humankind at the moment to know.”

That leaves the battle between dark matter and alternate models of gravitation at an impasse. However, Binney points out that dark matter has an advantage because it can also be studied through observations of galaxy mergers and collisions between galaxy clusters. Also, there are many experiments that are currently searching for evidence of dark-matter particles.

McGaugh’s next step is to extend the study to elliptical and dwarf spheroidal galaxies, as well as to galaxies at greater distances from the Milky Way.

The research is to be published in Physical Review Letters and a preprint is available on arXiv.

Spotlight on the International Year of Light (IYL 2015)

[brightcove videoID=4711383758001 playerID=106573614001 height=330 width=500]

By James Dacey

As science-inspired global initiatives go, it’s fair to say that the International Year of Light and Light-based Technologies (IYL 2015) burned brighter than its organizers could have imagined. IYL 2015 set out to raise awareness of the crucial roles light can play in areas such as sustainable development, education and health, and it did so through festivals, workshops, publications and a plethora of other activities. A final report published this week details some of IYL 2015’s key achievements and describes some of the year’s most memorable activities.

Among the highlights identified in the report is the Physics World film series “Light in our Lives”, a set of short documentaries about the role of light in people’s everyday lives. We commissioned the films as an official IYL 2015 media partner, embracing the collaborative and international dimensions of the year by working with filmmakers across the world. They include a film about how LED lanterns are enabling students to study after sunset in a rural community in India, and another about how lighting technologies are bringing a modern twist to Day of the Dead celebrations in Mexico City (see above).

(more…)

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