Quantum interference involving three photons has been measured by two independent teams of physicists. Seeing the effect requires the ability to deliver three indistinguishable photons to the same place at the same time and also to ensure that much more common single-photon and two-photon interference effects are eliminated from the measurements. As well as providing deep insights into the fundamentals of quantum mechanics, three-photon interference could also be used in quantum cryptography and quantum simulators.
When a stream of single photons travel through a double slit they will build up an interference pattern on a detector behind the slits – an example of single-photon interference. An example of two-photon interference is the Hong–Ou–Mandel (HOM) effect, which involves two photons entering a beam splitter with two exit ports. If the photons are identical and arrive at the same time, they will interfere and will always exit the same port of beam splitter. If these two criteria are not met, there is a 50% chance of each photon exiting either port.
Trio in a tritter
Now, a three-photon version of the HOM effect has been created by team led by Ian Walmsley of the University of Oxford in the UK. Their experiment begins with the creation of three independent photons in three different sources. These are sent to a fibre-optic based interferometer called a tritter, which has three inputs and three outputs. The team looked at the probability that all three photons exited the same output portal. To isolate the effects of single- and two-photon interference, they control something called the “triad phase” of the three photons. This is non-zero only if the photons are partially distinguishable – but not fully distinguishable. They were able to show that the probability for three photons emerging from one port varied with the triad phase, just as expected for three-photon interference. And crucially, single- and two-photon effects remained constant.
Meanwhile at the University of Waterloo in Canada, Thomas Jennewein and colleagues did their experiment using a photon source that emits three photons in an entangled quantum state. The trios are created by firing a single photon into a series of nonlinear crystals, each of which is able to convert one photon into a pair of entangled photons. Very occasionally an entangled trio emerges and is then sent into an interferometer that has two output ports. By changing the relative phases of the three photons, Jennewein’s team saw the probability of three photons emerging from one port vary as expected from three-photon interference. The probability of two photons emerging from the same port remained the same, however, suggesting that the team was observing genuine three-photon interference.
One possible application of the three-photon interference created in the experiments is three-photon sharing. This involves a secret quantum key that is shared by three parties, but can only be used by all three parties together. Three-photon interferometry could find use in quantum-sensing applications and also in a quantum-computing technique called boson sampling.
Science has taken motor racing to a whole new, extremely small level with the NanoCar Race. The competition on 28 April will see nanoscale molecular machines “speed” around a gold racetrack for 38 hours. As the tiny-molecule cars are not visible to the naked eye, the race will take place inside a scanning tunnelling microscope (STM) at the Center for the Development of Materials and Structural Studies (CEMES), part of the National Center for Scientific Research (CNRS) in France. The teams behind the NanoCars control their vehicles using electric pulses but are not allowed to push them mechanically. Details about the cars and their teams can be found on this website, where you will also be able to watch the race later this month. There is more about the competition in the above video.
A group of physicists in China has taken the lead in the race to couple together increasing numbers of superconducting qubits. The researchers have shown that they can entangle 10 qubits connected to one another via a central resonator – so beating the previous record by one qubit – and say that their result paves the way to quantum simulators that can calculate the behaviour of small molecules and other quantum-mechanical systems much more efficiently than even the most powerful conventional computers.
Superconducting circuits create qubits by superimposing two electrical currents, and hold the promise of being able to fabricate many qubits on a single chip through the exploitation of silicon-based manufacturing technology. In the latest work, a multi-institutional group led by Jian-Wei Pan of the University of Science and Technology of China in Hefei, built a circuit consisting of 10 qubits, each half a millimetre across and made from slivers of aluminium laid on to a sapphire substrate. The qubits, which act as non-linear LC oscillators, are arranged in a circle around a component known as a bus resonator.
Initially, the qubits are put into a superposition state of two oscillating currents with different amplitudes by supplying each of them with a very low-energy microwave pulse. To avoid interference at this stage, each qubit is set to a different oscillation frequency. However, for the qubits to interact with one another, they need to have the same frequency. This is where the bus comes in. It allows qubits to transfer energy from one another, but does not absorb any of that energy itself.
“Magical interaction”
The end result of this process, says team member Haohua Wang of Zhejiang University, is entanglement, or, as he puts it, “some kind of magical interaction”. To establish just how entangled their qubits were, the researchers used what is known as quantum tomography to find out the probability of detecting each of the thousands of possible states that this entanglement could generate. The outcome: their measured probability distribution yielded the correct state on average about two thirds of the time. The fact that this “fidelity” was above 50%, says Wang, meant that their qubits were “entangled for sure”.
According to Shibiao Zheng of Fuzhou University, who designed the entangling protocol, the key ingredient in this set-up is the bus. This, he says, allows them to generate entanglement “very quickly”.
The previous record of nine for the number of entangled qubits in a superconducting circuit was held by John Martinis and colleagues at the University of California, Santa Barbara and Google. That group uses a different architecture for their system; rather than linking qubits via a central hub they instead lay them out in a row and connect each to its nearest neighbour. Doing so allows them to use an error-correction scheme that they developed known as surface code.
High fidelity
Error correction will be vital for the functioning of any large-scale quantum computer in order to overcome decoherence – the destruction of delicate quantum states by outside interference. Involving the addition of qubits to provide cross-checking, error correction relies on each gate operation introducing very little error. Otherwise, errors would simply spiral out of control. In 2015, Martinis and co-workers showed that superconducting quantum computers could in principle be scaled up, when they built two-qubit gates with a fidelity above that required by surface code – introducing errors less than 1% of the time.
Martinis praises Pan and colleagues for their “nicely done experiment”, in particular for their speedy entangling and “good single-qubit operation”. But it is hard to know how much of an advance they have really made, he argues, until they fully measure the fidelity of their single-qubit gates or their entangling gate. “The hard thing is to scale up with good gate fidelity,” he says.
Wang says that the Chinese collaboration is working on an error-correction scheme for their bus-centred architecture. But he argues that in addition to exceeding the error thresholds for individual gates, it is also important to demonstrate the precise operation of many highly entangled qubits. “We have a global coupling between qubits,” he says. “And that turns out to be very useful.”
Quantum simulator
Wang acknowledges that construction of a universal quantum computer – one that would perform any quantum algorithm far quicker than conventional computers could – is not realistic for the foreseeable future given the many millions of qubits such a device is likely to need. For the moment, Wang and his colleagues have a more modest aim in mind: the development of a “quantum simulator” consisting of perhaps 50 qubits, which could outperform classical computers when it comes to simulating the behaviour of small molecules and other quantum systems.
Xiaobo Zhu of the University of Science and Technology of China, who was in charge of fabricating the 10-qubit device, says that the collaboration aims to build the simulator within the next “5–10 years”, noting that this is similar to the timescale quoted by other groups including the one of Martinis. “We are trying to catch up with the best groups in the world,” he says.
A lizard can change its spots, and now scientists have shown that the process is a living version of a popular computing algorithm. The ocellated lizard begins life with brown skin that is peppered with white spots. As the creature ages, the skin pattern transforms to a labyrinthine pattern in which each individual scale is either green or black. Now, a team of scientists in Switzerland and Russia has shown that this transformation is governed by a process that they call a “living cellular automaton”. In the field of computing, a cellular automaton consists of connected cells whose individual behaviour depends on the states of neighbouring cells. Computational cellular automatons have been used in a wide range of applications from simulating biological systems to creating computer games. In this latest work, Liana Manukyan of the University of Geneva and colleagues used a high-resolution system of robotic cameras to image the skin of three male lizards as they grew to adulthood. This allowed them to watch about 1500 scales on the back of each lizard change colour over a period of four years. Unlike many other animals, in which colour patterns are determined by interactions within individual cells, the results suggest that the colour of an individual cell (lizard scale) is determined by that of its neighbours. The team says that this is the first time that a cellular automaton has been seen in a living organism. Further studies into the chemical and biological processes involved in the skin transformation could provide important insights into why patterns emerge in living systems. The study is described in Nature.
Graphene keeps a lid on liquid analysis
Carbon caps: graphene sheet keeps liquid samples in channels during high vacuum PEEM analysis. (Courtesy: A Strelkov / NIST)
Graphene lids allow liquids to be analysed with a technique usually limited to solid samples. Andrei Kolmakov, from the National Institute of Standards and Technology (NIST) in the US and colleagues have developed a carbon-capped liquid sample array to extend the capability of photoemission electron microscopy (PEEM). The analysis tool involves bombarding a sample with ultraviolet light or X-rays. The photons transfer energy to electrons within the sample, allowing them to escape the material if they are near to the surface. The energy of an emitted electron is specific to the atom it came from, and therefore by using a series of electric lenses and detection systems, PEEM can create an image of the sample’s chemical make-up. Although a popular and powerful tool, PEEM is usually restricted to solid surfaces as liquid samples evaporate and create sparks under the required high vacuum. Kolmakov and team used graphene – an atomically thin sheet of carbon – to seal liquid or gas samples within a multi-channel array. Once the system is under vacuum, the samples are constrained to their channels and remain at atmospheric pressure, but photons and electrons can pass through the graphene nearly completely unimpeded. The simple solution, described in Nano Letters, allows researchers to analyse liquid interfaces and the surface of nanometre-scale objects immersed within liquid, potentially leading to the advancement of batteries and chemical catalysts.
Electron pulses outrun atoms
Electron pulses so short that atoms have no chance to move as the pulses pass through them have been produced by scientists working on the Pegasus radiation facility at the University of California, Los Angeles. The pulses are less than 10 fs in duration and could be used to do time-resolved electron microscopy studies such as following the motions of individual atoms in materials undergoing structural reorganization. Jared Maxson and colleagues created electron pulses of less than 10 fs duration using an electron source similar to those used to deliver electron bunches to synchrotron storage rings. The process begins with firing a 100 fs laser pulse at a cathode, which ejects a pulse of electrons. This relatively long pulse is then sent down a linear accelerator, where it is compressed in time to 10 fs. The final energy of the pulses – which each contain about 500,000 electrons – is several MeV, which is higher than the 50–300 keV used in conventional electron microscopes. While using higher-energy pulses does introduce several challenges, it also offers advantages that arise from relativistic effects in the higher-energy pulses. The research is 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 device that entangles 10 qubits.
Scientists studied this 250-year-old violin in an X-ray beamline at Italy’s Elettra synchrotron. (Courtesy: Elettra)
You can hardly blame the Norwegian musician Peter Herresthal for never letting anyone else play his 250-year-old violin. He bought it at an auction, with the help of a sponsor, for an eye-watering half a million dollars. “I don’t even let it out of my sight,” Herresthal told me. So for him to hand over the violin in October 2010 to a team of scientists at the Elettra synchrotron in Trieste, Italy – and then let them enclose it inside an X-ray beamline for two days – was a stupendous display of trust in science.
Operational since 1993, the Elettra facility has 27 different X-ray beamlines that are put to different uses. One beamline, known as SYRMEP (SYnchrotron Radiation for MEdical Physics), is often used by scientists to non-invasively examine archaeological specimens and ancient artefacts, including flutes and paper-pipe organs. These studies inspired a team of Elettra scientists to image a working violin – a cheap student model – with synchrotron light.
The resulting 3D images of the instrument – along with detailed information about its composition and manufacture – emboldened the researchers to seek a historically significant violin to image. Their thoughts immediately turned to the legendary “Cannon” violin that once belonged to the virtuoso Niccolò Paganini (1782–1840). One of the most famous instruments in the world, it was named after the explosive sounds Paganini could create with it.
Paganini’s Cannon is an Italian national treasure and is displayed in an earthquake-proof case in Genoa’s Palazzo Tursi; on the rare occasions it’s moved, it is ferried around in an armoured car. When the Elettra scientists approached its curator Alberto Giordano, he unsurprisingly didn’t feel comfortable lending it. Giordano, however, thought of his friend Herresthal, who had recently bought another historic violin, made in 1753 by the Piacenza instrument builder Giovanni Battista Guadagnini.
Herresthal was using the quality sound of the antique instrument to cement his reputation as a foremost expositor of contemporary violin music and also appeared reluctant. Although Giordano explained the procedure and assured Herresthal that the X-rays wouldn’t damage or alter the wood, Herresthal had other concerns too. “The violin’s wood is old and fragile,” he told me. “But the climate where I live in Norway is dry, and when you take the violin to a place with a different climate it affects the response.”
Herresthal eventually consented to the project but only after the Trieste scientists agreed to build a specially created environmental system that could control a sample’s temperature and humidity. And so it was that in October 2010 Herresthal and his wife put the violin in the back of their car and drove the 160 km down the autostrada from Venice, where he’d been teaching, to Trieste. Once there, a team of half a dozen scientists showed him the synchrotron and described how it works.
“They explained the technique, but I don’t know if I can explain it back!” Herresthal recalls. Staff then showed him the two-stage climate monitoring and control system they’d built. The first stage contained a humidifier and air conditioner designed to bring the climate to the target range of 55% relative humidity and 25 °C. The second consisted of a more precisely controlled environment inside a 50 × 50 × 130 cm Plexiglas box, equipped with an alarm that would ring in the control room should the humidity or temperature change.
Still, Herresthal’s first glimpse of Elettra’s experimental hall was a shock, crammed as it was with silver-foil-wrapped equipment and serviced by an overhead crane. “It looked like a scene from a James Bond movie just before everything blows up,” he says. “I remember how excited the scientists all were, but I was still worried.” Indeed, when Giordano asked Herresthal to remove his violin’s fittings to improve the imaging, Herresthal refused. He also said no when Giordano asked if the strings could be removed. “Hands off!” Herresthal recalls saying, worried about an upcoming performance in Kentucky. “If you remove the strings, the bridge can fall down.”
The scientists compromised, re-thinking their imaging plans. They mounted the violin on a support, closed off the experimental area from direct view, and began work. Two days later, they had a 3D digital image of the violin, resolving details down to 50 µm, presenting it in a way Herresthal could understand. “The images were remarkable,” he admits. “You could see all the repairs; I even saw a drop of glue.” When I asked Herresthal if the imaging changed his views about the violin, he agreed it had, saying it made him more confident. “It showed me there were no cracks and the repairs had been done well,” he says. “Sometimes you are tempted to open a violin to try to improve it; I’ll keep mine closed.” He also reckons violin imaging will change the market. “It won’t be possible to hide that a historic violin has cracks, or is heavily restored, or is made with composite materials.”
The critical point
One moment in this episode encapsulates what made the trust between Herresthal and the scientists possible, an encounter in which his respect for the scientists, and theirs for him, became most transparent. It took place after the first day, when the scientists had to stop to adjust the violin’s position. They asked Herresthal if he wanted to test it before they carried on.
Herresthal, still worried, said yes. If anything were awry he would refuse to let them continue. He picked up the violin, raised the bow, and started to play. Music filled the experimental hall – some scales, followed by snippets of a piece by a Danish composer that Herresthal was planning to perform in Kentucky.
Satisfied with the sound, Herresthal smiled. He handed them back the violin. and said: “Go ahead.”
The environment is a shared resource, and in recent years the question of how to moderate the impacts of human activity on the air, water and land has become increasingly important. One of the characteristics that has received the most attention in this effort is the “greenness” of our energy supply. Yet the term “green” seems not to be well understood and it is not consistently applied. Some sources define a “green” energy source as one with a low environmental impact, but that merely shifts the question towards defining impact. There is currently a lot of focus on greenhouse gases (GHGs), and many definitions seem to view “low impact” and “low-GHG emissions” as synonymous. Alternative definitions, however, include other types of environmental effects, such as particulate air pollution, use of water or the generation of waste products.
This confusion and multiplicity of definitions has particular implications for considering what the term “green” might mean for the nuclear-energy industry. Nuclear power is sometimes characterized as producing no GHGs, and while this is not completely true, it is certainly accurate to say that GHG emissions from nuclear power generation are much lower than those of fossil-fuel-based power sources.
Another characteristic of interest is the sustainability of different energy sources – that is, whether the supply could be “used up” over time. Simplistically, it would appear that both fossil fuels and uranium for nuclear power, being mined from the ground, are finite and will eventually be used up, while “renewable” resources such as wind and sunlight are effectively infinite. However, this viewpoint ignores the fact that the systems required to extract energy from sunlight and wind use mined materials as well.
Likewise, some consider the fact that nuclear power produces long-lived waste as proof that it is not “green”, yet a similar argument could be applied to the wastes generated in producing the components required for solar or wind power generation. All of these arguments – plus others relating to as-yet-untapped possibilities, such as reprocessing used nuclear fuel to extract more energy from it; using a thorium fuel cycle instead of (or in addition to) uranium; or even extracting uranium from unconventional resources, such as sea water – must be taken into account when deciding whether nuclear energy counts as “green”.
Cradle to grave
Unlike fossil fuels, which are all carbon-based and thus produce carbon dioxide when burned, “burning” uranium fuel produces no GHGs. However, other parts of the nuclear fuel cycle, including mining, extraction and enrichment of uranium, do produce some GHGs. This fact has been recognized in many analyses. What is less well recognized is that generating power from wind and sunlight also produces some GHGs.
1 Start to finish The life cycle of an energy-producing system can be split into three stages: the ‘front end’ (that is, steps before energy generation), ‘operations’ and the ‘back end’ after the system has reached the end of its useful life. With fossil fuels, most of the greenhouse gases (GHGs) come from combustion during the ‘operations’ phase, while for nuclear power and renewable energy sources, most of the GHG emissions come from the front end. For renewable energy sources, component manufacturing and facility construction produce the bulk of GHGs, while for nuclear power, enrichment accounts for more than half of the total GHG emissions.
This needs to be considered in any analysis of “greenness”, but often, it is not. The US Environmental Protection Agency (EPA) is one of many organizations to make this mistake. The EPA definition of green power is “electricity produced from solar, wind, geothermal, biogas, eligible biomass and low-impact small hydroelectric sources”. Thus, on their website it says that, “Although nuclear power generation emits no greenhouse gases during power generation, it does require mining, extraction and long-term radioactive waste storage.”
The EPA does not make a similar statement for solar or wind power. Yet, although solar and wind power – like nuclear power – emit no greenhouse gases during power operation, they also require raw materials to be mined, extracted and processed. In fact, because of the diffuse nature of wind and solar energy, more materials are required to construct and manufacture the structures and components for power production, per unit of energy generated, than are required for other energy sources. In addition, wind turbines use rare-earth metals, which are in limited supply, and the manufacture of solar photovoltaics involves the use of highly toxic materials.
Instead of simply identifying specific energy systems as “green” or “not green”, a better way to assess the “greenness” of energy sources is to examine the full set of environmental impacts from “cradle to grave”. This life-cycle assessment gives a more accurate idea of the total GHGs from any source. It makes it clear that all energy sources generate some GHGs, although the parts of the fuel cycle responsible for the emissions are different for each energy source (see “Start to finish”, above).
Another issue that must be addressed in evaluating GHG emissions is that different researchers have computed different levels of emissions. In 2013 the US National Renewable Energy Laboratory (NREL) reviewed a large number of studies and determined that the variation can be attributed to such factors as differences in the exact choice of designs assumed for each study, different operating assumptions and different evaluation methods. Despite these variations, however, all evaluations of the total life-cycle emissions show coal having significantly greater emissions than any other energy source (see “Measuring up”, above). Natural gas is the best of the fossil fuels in this respect, but it still produces significant emissions. Solar, wind, geothermal, hydro and nuclear power all generate only a small fraction of the GHGs of the larger emitters, with nuclear power usually ranking among the lowest emitters. Hence, if the measure of greenness is based on the emissions over the whole life cycle, nuclear power should be categorized as being similar to wind and solar power.
Waste not
In terms of non-GHG impacts, nuclear power and the renewable energy sources do not generate the particulates that are associated with coal burning, nor do they generate some of the other emissions associated with fossil fuels, such as methane, sulphur or nitrous oxides, organic compounds or toxic heavy metals. The nuclear-energy industry does, however, produce nuclear waste that must be sequestered for thousands of years before the radioactivity decays. The industry is often criticized for this, and its “green” credentials questioned on this basis. However, the volumes involved are small and waste repositories are being developed to ensure that the waste remains sequestered from the environment.
It is also worth noting that other energy sources are not waste-free. Coal produces large volumes of solid waste, in addition to the airborne emissions, but even renewable-energy sources produce waste. Frequently, the toxicity of this waste is an issue, but in some cases even the sheer volume of waste creates challenges. For example, solar energy requires large arrays of solar panels, which degrade over time and must be replaced. For a small country such as Japan, the question of what to do with all these spent panels is already becoming a problem.
2 Measuring up A comparison of direct greenhouse-gas emissions (red bars) and full-life-cycle emissions (blue bars) produced by different energy technologies. Although biomass is essentially a carbon-based fuel, and thus generates large quantities of carbon dioxide when it is burned, it also absorbs carbon as it grows. After including the environmental impacts of mining, extraction and enrichment, the greenhouse-gas emissions from the full nuclear fuel cycle are revealed to be on a par with those of sources like wind and solar power, while all three are much less than those of fossil fuels. (Source: Annex III: Technology-cost and performance parameters. In Climate Change 2014: Mitigation of Climate Change. Contribution of Working Group III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change.)
The environmental impacts of mining are often mentioned as a consequence of using fossil or nuclear fuels. However, the volume of the resource needed for nuclear power operations is much less than that needed to burn fossil fuels, and this translates to a lower level of environmental impacts from extraction. Moreover, as already noted, renewable energy sources require the mining of large volumes of structural materials, as well as the mining of toxic materials. Although the environmental impacts are a lot smaller than for coal, there are some measurable impacts associated with these mining operations.
A detailed assessment of other types of environmental impact is beyond the scope of this article. A full comparison of energy sources would include such factors as land use, which is greater for solar power and wind than for other sources (although some solar and wind sites can be used for other purposes, such as agriculture in the case of wind farms); impacts on birds and bats (a concern for wind farms); accidents (serious accidents at nuclear power plants can contaminate surrounding areas); earthquakes (from hydroelectric dams and fracking for oil and gas); and impacts associated with disposing of wastes from the various energy sources (building and operating disposal facilities, transporting wastes, and so on).
No free lunch The real truth is that no energy source is completely green. Perhaps it is more accurate to say that there are shades of green. By that measure, nuclear power is very close to the same shade of green as that of most renewables.
But evaluating energy supply options is an incredibly complex and multi-faceted exercise, and while greenness is important, it must be viewed in the context of other considerations. Decision-makers must weigh the GHG and other emissions from each energy source against such measures as cost; short- and long-term resource availability; the reliability of the overall energy supply 24 hours a day; and the security of the energy supply against interruptions by weather or by foreign suppliers.
These evaluations are not static. Resource discoveries and actions by foreign governments can affect supply, while technology developments and government decisions can affect a host of measures, including costs, availability, emissions and other measures. This article has considered only current energy-supply technologies, but a breakthrough in some areas could alter the comparative data significantly. One example of such a breakthrough would be “clean coal” technology – that is, some way of extracting the GHGs from coal emissions before they are released to the environment, and sequestering them from the environment permanently and reliably. Since this type of development can’t be counted on at the current time, it is not considered in the comparative data used in this article. If it later proves to be technically feasible and economic, it could alter the discussion radically. So, too, could the development of fusion energy, or cheap energy storage for renewables.
At present, though, no single energy source excels in all measures. Each has some pros and cons, and most rational national policies seek to diversify their energy portfolios in order to take advantage of the benefits different energy-supply technologies offer and to ameliorate any disadvantages. Although nuclear power has some challenges – notably waste disposal – it appears to be one of the most attractive sources in terms of a small environmental footprint, reliable energy generation, security of the energy supply, and other important measures. Hence, the short answer to the question raised in this article’s title is that nuclear energy is indeed green, and it offers several other advantages as well. It should, therefore, be considered in this light in decision-making on future energy-supply options.
Adding nanoparticles to the surface of tumour cells could make them more susceptible to treatment with particular cancer drugs, according to new research at MIT. The study showed that nanoparticles tethered to the cell surface can increase the effects of forces exerted on the tumour cells by physiological fluids flowing within the body, which makes the cells much more vulnerable to attack by certain therapeutics.
Scientists have recently been exploring the physical properties of tumours and their microenvironment, with recent research showing that tumours can exploit the forces in their surroundings to enhance their survival and promote the progression of the cancer. But researchers at MIT believe that increasing the forces exerted on tumour cells can make certain therapeutics more effective in killing cells and controlling the cancer.
The study, which was led by Robert Langer, used an experimental drug known as TRAIL (a TNF-related apoptosis-inducing ligand), which exerts a cytotoxic effect on tumour cells without damaging healthy cells. TRAIL also avoids many of the debilitating effects of more commonly used therapies.
The researchers found that when used to target tumour cells, TRAIL was more successful in killing cancerous cells once they had been exposed to the shear forces generated by physiological fluids such as blood flow in the body (Nat. Commun.8 14179). The MIT team set out to optimize the forces required for cell death, and they found that increasing the force on the cells made them more susceptible to TRAIL.
Nanoparticles strengthen forces
To produce these forces, Langer and his colleagues have pioneered the use of nanoparticles made from biodegradable polymers known as PLGA (poly(lactic-co-glycolic acid)). When injected into the bloodstream, the nanoparticles attach to the tumour cell surface and increase the force on the cell from the flow of physiological fluids.
Members of the MIT research team: Michael Mitchell, Amanda Chung, and Pedro Guimaraes
The nanoparticles are coated with PEG (polyethylene glycol), which is tagged with a specific ligand that interacts with proteins found on the surface of the tumour cells. These ligands, and therefore the nanoparticles, are attached to the tumour cell like a ball tied to a string. The shear forces from the flow of physiological fluids cause the nanoparticles to bump and bash the tumour cells, causing them to become more susceptible to the effects of the therapeutics.
The MIT team found that attaching the nanoparticles to tumour cells prior to treatment with TRAIL killed metastatic tumours and reduced the progression of tumours in mice. The researchers also found that the treatment appeared to be specific to tumour cells and that healthy cells remained unaffected. Nanoparticle size and quantity were also found to have an effect on cell death. Larger particles, around one micrometre across, and a higher quantity of particles were found to have the most positive effect.
The researchers believe that the mechanism the nanoparticles induce on the tumour cells may cause the molecules surrounding the tumour cells to compress, enabling the therapeutics to interact more efficiently with receptors on the cell surface.
Langer and his research team are now exploring the possibilities of using this technique in combination with other drugs. This is a key strategy to prevent drug resistance in cancer treatment since tumours often regrow and become unaffected by drugs that had previously been effective. The MIT team is particularly interested in drug combinations that induce cytokines, which stimulate signalling chemicals that trigger an immune response to the site that helps destroy the tumour.
Horseshoe bats wiggle their ears and noses to boost their ability to navigate using ultrasound. That is the conclusion of Rolf Müller of Virginia Tech and colleagues, who have done mechanical and computer simulations that show that the wiggles could improve the bats’ ability to resolve direction by up to a factor of 1000. A horseshoe bat emits ultrasound from its nose and detects the reflected signal using its ears. The creature’s nose and ears have complex external structures – called noseleaves and pinnae, respectively – that diffract sound waves upon emission and reception. Bat experts also know that the shapes of the noseleaves and pinnae can change rapidly and that this has an effect on the sound used for echolocation. To understand why, Müller’s team created robotic models of noseleaves and pinnae and measured their acoustic properties when they were wiggled to mimic living bats. When combined with computer simulations, the measurements suggest the wiggling can result in a 100–1000 fold improvement in direction resolution over what can be achieved with static noseleaves and ears. Writing in Physical Review Letters, the researchers point out that very little is known about how bats use echolocation to navigate in complex natural environments. They suggest that a better understanding of the dynamic nature of the noseleaves and pinnae could boost our understanding of these incredible creatures and also lead to navigation technology inspired by bats.
Pressure helps supercooled water flow
The viscosity of supercooled water decreases by 42% when under pressure, according to scientists in France. Usually liquids become thicker when pressure is increased, but more than a century ago the opposite was observed to happen for water below 32 °C. This occurs because the application of pressure breaks the intermolecular hydrogen bonds that provide the water with its unusual properties. As the network of hydrogen bonds increases with cooling, the effect of pressure should be stronger. Frédéric Caupin and colleagues at the University of Lyon have studied this phenomenon in supercooled water – liquid water below the freezing point – which is a difficult feat as the liquid is liable to crystallize. Using a time-of-flight viscometer, the team measured water flow for temperatures down to –29 °C and pressures up to 3000 atmospheres. Finding that the viscosity decreased by nearly a half, Caupin and colleagues propose a model that treats water as a mixture of two species – a high-density “fragile” liquid and a low-density “strong” liquid. As described in PNAS, the ratio of these fluids explains water’s unusual thermodynamic and dynamic properties.
BELLE II detector rolls into collision point
Starting point: BELLE II before it started its voyage. (Courtesy: KEK)
The BELLE II particle detector has been moved 13 m from its place of assembly to a collision point on the SuperKEKB collider in Japan. The SuperKEKB accelerator is an electron–positron collider that is designed to create large numbers of B-mesons. It is a major upgrade to the KEKB collider, which operated in 1998–2010 and included the Belle detector. In 2001, Belle discovered the existence of charge–parity symmetry violation (CP violation) with B-mesons. This confirmed the theoretical prediction of Makoto Kobayashi and Toshihide Maskawa, who shared the 2008 Nobel Prize for Physics for that work. SuperKEKB will achieve a collision rate that is about 40 times higher than KEKB, and BELLE II is designed to collect much more data than Belle and operate at a much improved measurement precision. Standing 8 m tall and weighing 1400 tonnes, BELLE II is expected to start taking data in 2018. It will do further studies of CP violation as well as perform searches for physics beyond the Standard Model.
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A $12 device that can measure the mass of microgram-sized objects in fluid has been developed by researchers in the US. The sensor is driven by a piezoelectric speaker and measures the change in the resonant frequency of a glass tube as the object passes through it. The team used the device to measure mass changes in several biological samples and says that the sensor has applications in a wide range of fields, such as developmental biology, toxicology, materials science and plant science.
Mass is an important physical measurement that can provide crucial information about the nature of an object. However, weighing microgram-sized biological samples such as embryos in liquid, can be very tricky indeed. While mass measurements can offer valuable insights into the biological state and health of such specimens, they cannot be easily made with standard laboratory equipment.
Nanogram resolution
To tackle this shortcoming, William Grover and colleagues at the University of California, Riverside, have created a simple mass sensor from off-the-shelf electronics and a short length of glass tubing bent into a “U” shape. The glass tube is attached to a small speaker and the bottom of the “U” passes through a photointerrupter – a device that uses an LED and a light sensor to detect the presence, or not, of an object. This simple set-up cost around US$12, yet can determine the mass of a microgram-sized object with a resolution of a few hundred nanograms.
It provides a pretty complete picture of the physical properties of a sample
William Grover, University of California, Riverside
The speaker keeps the glass tube vibrating at its resonant frequency using a simple feedback circuit from the photointerrupter, which detects the oscillation rate. As the object being weighed is pumped through the tube it changes the tube’s resonance frequency. This change is detected by the photointerrupter and can be used to calculate the objects mass, volume and density.
“If the object has a different density than the fluid, then it will change the sensor’s mass when it flows through,” explains Grover. “If the object is denser than the fluid around it, it’ll make the sensor slightly heavier and that makes the sensor’s frequency go down. If the object is less dense than the fluid, it makes the sensor slightly lighter and that makes the sensor’s frequency go up. By measuring these frequency changes, we measure the buoyant mass of the object.”
Germinating seeds
The sensor was calibrated with microbeads of known mass. The team then demonstrated that it can measure changes in the mass of zebra-fish embryos – a common model for embryological development studies – as they react to toxins. The device was also used to measure the degradation rates of nano-sized biomaterials used in medical implants, as well as mass and density changes in germinating seeds.
“It’s fundamentally a mass sensor, so at the most basic level it can weigh tiny objects in fluid,” says Grover. “But by using a method that Archimedes first described over 2000 years ago, we can also use it to measure the volume and density of the objects. So it provides a pretty complete picture of the physical properties of a sample.”
Grover expects the sensor to have many applications, but he is especially interested in using it to “study the development of organisms, measure biodegradable materials, and monitor the environment”. The new device is described in PLOS ONE.
Nitrogen-vacancy (NV) centres on two different diamonds have been coupled coherently by physicists in Austria. NV centres occur whenever two neighbouring carbon atoms in diamond are replaced by a nitrogen atom and an empty lattice site. NV centres are being used to develop quantum technologies because they have spin states with very long quantum-coherence times, even at room temperature. Another important benefit of NV centres is that they interact with both light and microwave radiation and could therefore act as a transducer between quantum devices based on the two types of radiation. Now, Johannes Majer and colleagues at the Technical University of Vienna have created quantum-coherent interactions between NV centres in two different pieces of diamond separated by about 5 mm. The diamonds are placed on two different microwave cavities, which are connected by a microwave-resonator transmission line. A static magnetic field is applied to the system and this tunes the transition energies of the NV spins to correspond to the microwave energy of the cavity – causing the NV spins to couple to the cavity. Because microwave radiation can travel through the transmission line between the two cavities, the NV centres in both diamonds can be coupled to each other. The team showed that when the crystalline structures of both diamonds are aligned, then the NV centres in both diamonds are coupled in a quantum-coherent manner. “This interaction is mediated by the microwave resonator in the chip in between; here, the resonator plays a similar role to that of a data bus in a regular computer,” says Majer. The coupling can also be switched off, allowing the NV centres of each diamond to be manipulated independently. While the researchers were not able to show that the NV centres on different diamonds were entangled quantum-mechanically, they write in Physical Review Letters that achieving and measuring entanglement could be an “interesting future challenge”.
Martian metals unlike Earth’s
Alien behaviour: Mars’ ionosphere has a structure unlike Earth’s. Artist’s concept showing MAVEN spacecraft over Mars. (Courtesy: NASA’s Goddard Space Flight Center)
Metal ions in Mars’ atmosphere have been directly detected for the first time, and the distributions are distinctly different to those on Earth. Scientists have extensive knowledge of Earth’s ionosphere – a region of high-energy electrons, ions and charged molecules in the upper atmosphere, resulting from the ionization of meteorite dust entering at high speed. Due to Earth’s magnetic fields, gravity and ionospheric winds, the metallic ions – mainly magnesium (Mg+) and iron (Fe+) – are forced into layers. Investigations into the ionospheres of other planets have been modelled upon Earth’s example and have been reliant upon indirect measurements from Earth or satellites. But now, NASA‘s Mars Atmosphere and Volatile Evolution (MAVEN) mission has not only made the first direct detection of ions on a planet other than Earth, but also found that they behave differently. MAVEN’s spectrometer has detected sodium (Na+), Mg+ and Fe+ continuously over the last two years, implying the ions are a permanent feature. But rather than Earth’s distinct layers, there is no separation of the light Mg+ and the heavy Fe+ with increasing altitude as expected because of gravity. Instead the metals are mixed with the neutral atmosphere at altitudes where no mixing process is expected. Joseph Grebowsky of NASA’s Goddard Space Flight Center in the US and team suggest this is because Mars only has localized magnetic fields in certain regions of the crust and so layering only occurs there. The aim of the MAVEN mission is to investigate how Mars lost most of its air, and the new results, published in Geophysical Research Letters give a new insight into predicting the atmospheres of other planets.
Canadian science panel calls for increased spending
Canadian science requires a billion dollar increase to avoid falling behind other nations in basic science. That is the main conclusion of a report released yesterday by a nine-strong panel led by David Naylor, former president of the University of Toronto, which also included the Nobel laureate Art McDonald and Blackberry co-founder Mike Lazaridis. The panel say that Canada needs to invest an additional C$1.3bn over the next four years to boost the science base – taking the county’s science budget to C$4.8bn – recommending that about C$500m of that increase should be diverted to basic research. The panel also calls on the government to set up a National Advisory Council on Research and Innovation that would advise the Canadian government on research priorities and also “provide broad oversight of the federal research and innovation ecosystem”. The Fundamental Science Review was commissioned last year by science minister Kirsty Duncan to review the state of science in Canada. The publication of the report comes after the Canadian government disappointed scientists last month with a flat budget for science in 2017.
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 $12 sensor that can weigh microgram-sized objects.
