physicsworld--2020-12-07--Nanomesh pressure sensor preserves skin’s sense of touch

Researchers in Japan have developed the first artificial-skin patch that does not affect the touch sensitivity of the real skin beneath it .
The new ultrathin sensor , which is made from multilayers of conductive and dielectric nanomesh structures , could be used in applications as diverse as prosthetics , robot-assisted surgery , human-machine interfaces and wearable health care monitors .
Skin is our largest sensory organ , with an abundance of neurons that continually monitor stimuli in our environment and transmit this information to the brain .
A good artificial skin must replicate this ability .
In particular , @ @ @ @ @ @ @ needs to be highly sensitive to touch , while also responding quickly to applied pressure .
To achieve these goals , the e-skin needs to incorporate a high density of sensors , over areas at least as small as 50 microns .
But they also need to avoid interfering with a person ’ s natural sense of touch , and this has proved difficult .
Human fingertips , for example , are so sensitive that a piece of plastic foil just a few microns thick is enough to impair a person ’ s @ @ @ @ @ @ @ your fingers has to be extremely thin , ” explains Sunghoon Lee , a member of Takao Someya ’ s group at the University of Tokyo and an author of the paper .
“ But this obviously makes it very fragile and susceptible to damage from rubbing or repeated physical actions.
” For this reason , Lee adds , most e-skins developed to date – made from , for example , sensor arrays of assembled nanowires or microstructure rubber layers that change capacitance or resistance in response to pressure or force – have @ @ @ @ @ @ @ contrast , the sensor developed by Someya , Lee and colleagues is thin and porous .
It consists of two layers , both made using a process called electrospinning , and is based on a design proposed by Akihito Miyamoto and colleagues in 2017 .
The first layer is an insulating mesh-like network comprising polyurethane fibres around 200 to 400 nm thick .
The second is a network of lines that makes up the functional electronic part of the device – a parallel-plate capacitor .
This is made of gold on a supporting @ @ @ @ @ @ @ , a water-soluble polymer often found in contact lenses .
Once this layer has been fabricated , the researchers wash away the PVA to leave only the gold support .
The finished pressure sensor is around 13 microns thick .
When a finger covered with this sensor grasps an object , the dielectric nanomesh layer deforms , producing a change in the capacitance measured between the two layers .
When the researchers evaluated the device ’ s sensitivity as determined by the slope of the capacitance change-pressure curve , they found values ( @ @ @ @ @ @ @ pressure range of less than 1 kPa and 0.010 kPa-1 in the high applied pressure range of more than 10 kPa ) that were comparable to the grip forces measured for a bare finger .
“ We performed a rigorous set of tests on our sensors with the help of 18 test subjects , ” Lee says .
“ They confirmed that the sensors were imperceptible and affected neither the ability to grip objects through friction , nor the perceived sensitivity compared to performing the same task without a sensor attached .
This @ @ @ @ @ @ @ for.
” As an added benefit , the researchers found that their nanomesh sensors continued to work even after being compressed repeatedly .
Indeed , the devices ’ capacitance changed by just 0.15 % after they had been squeezed 1000 times at 19.6 kPa .
The conductivity of the gold electrode also remained relatively stable during these experiments .
Another point in favour of the sensor is its resistance to friction : tests showed that it could be rubbed 300 times with a 50 g object ( equivalent to applied pressures of more @ @ @ @ @ @ @ The sensor ’ s electrical characteristics changed only slightly during these tests , and the device remained sensitive to applied pressures even after being rubbed .
The researchers , who report their work in Science , say they plan to increase the number of sensing points in their device and determine how pressure is spatially distributed across it .
“ We also hope to further develop other imperceptible sensors , such as temperature , strain and humidity sensors , to achieve multimodal sensing , ” Lee tells Physics World .

The polyurethane and gold sensor can resist shear forces and rubbing. (Credit: © 2020 Someya et al.)
Researchers in Japan have developed the first artificial-skin patch that does not affect the touch sensitivity of the real skin beneath it. The new ultrathin sensor, which is made from multilayers of conductive and dielectric nanomesh structures, could be used in applications as diverse as prosthetics, robot-assisted surgery, human-machine interfaces and wearable health care monitors.
Skin is our largest sensory organ, with an abundance of neurons that continually monitor stimuli in our environment and transmit this information to the brain. A good artificial skin must replicate this ability. In particular, an electronic skin, or e-skin, needs to be highly sensitive to touch, while also responding quickly to applied pressure.
To achieve these goals, the e-skin needs to incorporate a high density of sensors, over areas at least as small as 50 microns. But they also need to avoid interfering with a person’s natural sense of touch, and this has proved difficult. Human fingertips, for example, are so sensitive that a piece of plastic foil just a few microns thick is enough to impair a person’s sensations.
“A wearable sensor for your fingers has to be extremely thin,” explains Sunghoon Lee, a member of Takao Someya’s group at the University of Tokyo and an author of the paper. “But this obviously makes it very fragile and susceptible to damage from rubbing or repeated physical actions.”
For this reason, Lee adds, most e-skins developed to date – made from, for example, sensor arrays of assembled nanowires or microstructure rubber layers that change capacitance or resistance in response to pressure or force – have been relatively thick and bulky.
Two layers
In contrast, the sensor developed by Someya, Lee and colleagues is thin and porous. It consists of two layers, both made using a process called electrospinning, and is based on a design proposed by Akihito Miyamoto and colleagues in 2017. The first layer is an insulating mesh-like network comprising polyurethane fibres around 200 to 400 nm thick. The second is a network of lines that makes up the functional electronic part of the device – a parallel-plate capacitor. This is made of gold on a supporting scaffold of polyvinyl alcohol (PVA), a water-soluble polymer often found in contact lenses. Once this layer has been fabricated, the researchers wash away the PVA to leave only the gold support. The finished pressure sensor is around 13 microns thick.
When a finger covered with this sensor grasps an object, the dielectric nanomesh layer deforms, producing a change in the capacitance measured between the two layers. When the researchers evaluated the device’s sensitivity as determined by the slope of the capacitance change-pressure curve, they found values (of 0.141 kPa-1 in the low applied pressure range of less than 1 kPa and 0.010 kPa-1 in the high applied pressure range of more than 10 kPa) that were comparable to the grip forces measured for a bare finger.
“We performed a rigorous set of tests on our sensors with the help of 18 test subjects,” Lee says. “They confirmed that the sensors were imperceptible and affected neither the ability to grip objects through friction, nor the perceived sensitivity compared to performing the same task without a sensor attached. This is exactly the result we were hoping for.”
Robust and resistant
As an added benefit, the researchers found that their nanomesh sensors continued to work even after being compressed repeatedly. Indeed, the devices’ capacitance changed by just 0.15% after they had been squeezed 1000 times at 19.6 kPa. The conductivity of the gold electrode also remained relatively stable during these experiments.
Another point in favour of the sensor is its resistance to friction: tests showed that it could be rubbed 300 times with a 50 g object (equivalent to applied pressures of more than 100 kPa) without breaking. The sensor’s electrical characteristics changed only slightly during these tests, and the device remained sensitive to applied pressures even after being rubbed.
The researchers, who report their work in Science, say they plan to increase the number of sensing points in their device and determine how pressure is spatially distributed across it. “We also hope to further develop other imperceptible sensors, such as temperature, strain and humidity sensors, to achieve multimodal sensing,” Lee tells Physics World.


physicsworld--2020-12-06--New fuel gauge for spacecraft could keep satellites active for longer

When a spacecraft launches , it uses roughly 75–90 % of its propellant getting into orbit .
The remaining fraction determines how long it can remain up there , but gauging how much fuel is left in the tank is no easy task in zero gravity .
Researchers at the US National Institute of Standards and Technology have now developed a solution based on a suite of sensors that detects the capacitance of liquid inside a spacecraft ’ s fuel tank and uses these data to reconstruct a three-dimensional picture of the remaining fuel .
According to the team , @ @ @ @ @ @ @ operate for longer , while also helping to avoid damaging end-of-life collisions .
Under zero-gravity conditions , liquid propellants adhere to the inside of fuel tank walls due to surface tension and capillary effects .
This unpredictable spatial distribution makes fuel levels hard to determine .
Propellants are also free to slosh about , float and form bubbles – none of which happens on Earth .
Several techniques have been developed to measure onboard spacecraft propellant .
One of the most common , known as the bookkeeping technique , involves estimating how much @ @ @ @ @ @ @ this from the volume of fuel left in the tank .
However , while this method is highly accurate at the beginning of a mission , the error of each estimate carries over to the next and accumulates with each thrust , explains team member Nick Dagalakis , a mechanical engineer .
“ By the time a tank is low , the estimates become more like rough guesses and can miss the mark by as much as 10 % , ” he says .
Without reliable fuel measurements , satellite operators are in @ @ @ @ @ @ @ a satellite when it still has plenty of fuel left is a waste of money , but letting the tank run dry could leave the satellite stranded , with no fuel left to evade other craft or move to a safe orbit .
The new fuel gauge , which was developed by NASA technology transfer manager Manohar Deshpande , relies on a 3D imaging technique called electrical capacitance volume tomography ( ECVT ) .
Tomography in general is a way of imaging the internal structure of an object without damaging it ; familiar @ @ @ @ @ @ @ MRI ) , positron emission tomography ( PET ) and X-ray tomography routinely employed in hospitals .
ECVT is a more recent variant , and it uses an array of sensors that emit electromagnetic waves .
These waves can be detected by the other sensors in the array , and how well they are transmitted depends on the capacitance of whatever lies between the sensors .
If there is nothing there , transmission will be high .
However , if an object is present , transmission will drop since the object will absorb @ @ @ @ @ @ @ placing these sensors around a container , and measuring the signal at many locations , it is therefore possible to build up a 3D picture of the objects inside the container .
To make their ECVT sensors , Dagalakis and colleagues used soft lithography to print wax-coated solid inks onto paper-thin laminated copper sheets .
They then etched the copper strips to remove the inks and form the patterns of the sensors and their electrical connections .
Dagalakis notes that because the sensors can be made using well-known MEMS fabrication techniques , the @ @ @ @ @ @ @ their gaps and shielding strips can be set with a high degree of accuracy .
These fabrication techniques also eliminate the need to solder electrical wires on the plates and strips and route wires through the sensor arrays and tank structures .
Finally , since the strips are flexible , they can be applied to the interior of an egg-shaped vessel – like a spacecraft fuel tank .
Many liquid propellants ( including liquid hydrogen and hydrazine ) are highly flammable in the Earth ’ s atmosphere .
As a safer alternative , @ @ @ @ @ @ @ a fuel substitute that has a dielectric constant similar to that of real spacecraft propellant but is stable in air .
The researchers placed their sensors around a test tank ( a miniature version of a real NASA fuel tank ) and measured the difference in transmission of every possible sensor pair in their array .
By combining these measurements , they determined where the tank contained fuel and where it did not , gradually building up a 3D image of the fuel content along the length of the tank .
Their reconstructed @ @ @ @ @ @ @ real shapes of the liquid inside the tank .
To better understand how this system would perform in space , the NIST team suspended a fluid-filled balloon inside the test tank , mimicking a liquid droplet in microgravity .
They then input the resulting capacitance data into a software program to produce a series of 2D images , which they subsequently compiled to produce a 3D rendition of the balloon .
The balloon ’ s measured diameter differed by less than 6 % relative to its actual diameter .
As well as gauging @ @ @ @ @ @ @ ECVT sensor could help overcome other problems related to liquids in space .
For example , Deshpande suggests that it might be used to continuously monitor fluid flow in the many pipes aboard the International Space Station and study how sloshing fluids can alter the trajectory of spacecraft and satellites .
The researchers , who report their experiments in the Journal of Spacecraft and Rockets , plan to further test and explore various image reconstruction techniques .
They are also studying ways to incorporate their sensors into new generations of long-distance spacecraft .
@ @ @ @ @ @ @ fabrication of these sensors may allow several of them to be used in a spacecraft or satellite fuel tank working independently to create a composite image of the total fuel volume , ” Dagalakis tells Physics World .
“ These sensors could have different sizes and shapes for covering the surface of the tank , any internal piping , fuel feeding pipes and fuel concentration structures .
”

Fuel gauges with higher accuracy could help ensure that satellites stay operational for longer and more is made of their time in orbit. (Credit: NASA Jet Propulsion Laboratory)
When a spacecraft launches, it uses roughly 75–90% of its propellant getting into orbit. The remaining fraction determines how long it can remain up there, but gauging how much fuel is left in the tank is no easy task in zero gravity. Researchers at the US National Institute of Standards and Technology have now developed a solution based on a suite of sensors that detects the capacitance of liquid inside a spacecraft’s fuel tank and uses these data to reconstruct a three-dimensional picture of the remaining fuel. According to the team, the prototype design could enable satellites to operate for longer, while also helping to avoid damaging end-of-life collisions.
Under zero-gravity conditions, liquid propellants adhere to the inside of fuel tank walls due to surface tension and capillary effects. This unpredictable spatial distribution makes fuel levels hard to determine. Propellants are also free to slosh about, float and form bubbles – none of which happens on Earth.
Several techniques have been developed to measure onboard spacecraft propellant. One of the most common, known as the bookkeeping technique, involves estimating how much is burned with each thrust and subtracting this from the volume of fuel left in the tank. However, while this method is highly accurate at the beginning of a mission, the error of each estimate carries over to the next and accumulates with each thrust, explains team member Nick Dagalakis, a mechanical engineer. “By the time a tank is low, the estimates become more like rough guesses and can miss the mark by as much as 10%,” he says.
Without reliable fuel measurements, satellite operators are in a bind, Dagalakis adds. Retiring a satellite when it still has plenty of fuel left is a waste of money, but letting the tank run dry could leave the satellite stranded, with no fuel left to evade other craft or move to a safe orbit.
An array of capacitance sensors
The new fuel gauge, which was developed by NASA technology transfer manager Manohar Deshpande, relies on a 3D imaging technique called electrical capacitance volume tomography (ECVT). Tomography in general is a way of imaging the internal structure of an object without damaging it; familiar examples include the magnetic resonance imaging (MRI), positron emission tomography (PET) and X-ray tomography routinely employed in hospitals.
ECVT is a more recent variant, and it uses an array of sensors that emit electromagnetic waves. These waves can be detected by the other sensors in the array, and how well they are transmitted depends on the capacitance of whatever lies between the sensors. If there is nothing there, transmission will be high. However, if an object is present, transmission will drop since the object will absorb some of the electromagnetic waves. By placing these sensors around a container, and measuring the signal at many locations, it is therefore possible to build up a 3D picture of the objects inside the container.
Sensor fabrication
To make their ECVT sensors, Dagalakis and colleagues used soft lithography to print wax-coated solid inks onto paper-thin laminated copper sheets. They then etched the copper strips to remove the inks and form the patterns of the sensors and their electrical connections.
The interior of the prototype fuel tank. (Credit: N Hanacek/NIST)
Dagalakis notes that because the sensors can be made using well-known MEMS fabrication techniques, the dimensions of the electro-capacitance plate arrays, their gaps and shielding strips can be set with a high degree of accuracy. These fabrication techniques also eliminate the need to solder electrical wires on the plates and strips and route wires through the sensor arrays and tank structures. Finally, since the strips are flexible, they can be applied to the interior of an egg-shaped vessel – like a spacecraft fuel tank.
3D image of fuel content
Many liquid propellants (including liquid hydrogen and hydrazine) are highly flammable in the Earth’s atmosphere. As a safer alternative, the researchers tested their sensor array using a fuel substitute that has a dielectric constant similar to that of real spacecraft propellant but is stable in air.
The researchers placed their sensors around a test tank (a miniature version of a real NASA fuel tank) and measured the difference in transmission of every possible sensor pair in their array. By combining these measurements, they determined where the tank contained fuel and where it did not, gradually building up a 3D image of the fuel content along the length of the tank. Their reconstructed images showed a good match with the real shapes of the liquid inside the tank.
Space simulations
To better understand how this system would perform in space, the NIST team suspended a fluid-filled balloon inside the test tank, mimicking a liquid droplet in microgravity. They then input the resulting capacitance data into a software program to produce a series of 2D images, which they subsequently compiled to produce a 3D rendition of the balloon. The balloon’s measured diameter differed by less than 6% relative to its actual diameter.
As well as gauging fuel, the researchers say the new ECVT sensor could help overcome other problems related to liquids in space. For example, Deshpande suggests that it might be used to continuously monitor fluid flow in the many pipes aboard the International Space Station and study how sloshing fluids can alter the trajectory of spacecraft and satellites.
The researchers, who report their experiments in the Journal of Spacecraft and Rockets, plan to further test and explore various image reconstruction techniques. They are also studying ways to incorporate their sensors into new generations of long-distance spacecraft.
“The flexible and inexpensive design and fabrication of these sensors may allow several of them to be used in a spacecraft or satellite fuel tank working independently to create a composite image of the total fuel volume,” Dagalakis tells Physics World. “These sensors could have different sizes and shapes for covering the surface of the tank, any internal piping, fuel feeding pipes and fuel concentration structures.”


physicsworld--2020-12-05--Sound waves in fermionic superfluid are studied in a ‘beautiful’ experiment

The acoustic properties of an ultracold fermion gas have been measured either side of the superfluid transition temperature in an experiment that has been described as “ near perfect ” and “ beautiful ” .
The results could have significant implications for understanding everything from superconductors to the aftermath of the Big Bang .
Superfluidity occurs at very low temperatures when bosons such as helium-4 form a single , macroscopic quantum ground state .
As well as being able to flow indefinitely without losing kinetic energy , a superfluid can famously climb uphill over a barrier to reach an energy @ @ @ @ @ @ @ can also form a superfluid by first pairing up to form bosons .
In helium-3 , the interactions between atoms are relatively weak .
However , strongly interacting Fermi gases , in which the mean free path of the particles is barely longer than the spacing between them , can also become superfluids .
These systems display markedly different properties from superfluid helium-3 and can not be described by the standard theory of superfluidity developed by the Soviet physicist and Nobel laureate Lev Landau .
Despite their strong interactions , these superfluids have @ @ @ @ @ @ @ ’ s paradigm just doesn ’ t work , ” says Martin Zwierlein of Massachusetts Institute of Technology .
Finding a theory that does , however , could be extremely useful because strongly interacting Fermi gases are widespread in physics .
“ Take , for example , the high temperature cuprate superconductors , in which electrons interact very strongly , ” explains Zwierlein .
“ The resistance of these materials is very difficult or impossible to calculate theoretically , we do not understand these materials.
” One way to investigate any unfamiliar material @ @ @ @ @ @ @ it and listen to the resulting sound waves .
“ Hilariously , this had not been done , ” he says , “ because for 25 years we had been using focused laser traps that were grabbing onto the atoms , creating a very inhomogeneous soup which had high density in the centre and low density at the edges – it was not nice for such an experiment.
” In the new research , Zwierlein and colleagues built a “ box trap ” using three laser beams .
“ We shape light , @ @ @ @ @ @ @ can , and as this light is repulsive , whenever atoms hit the walls they bounce back into the box , ” he says .
First , the researchers measured the speeds at which various acoustic waves propagated through the gas in both the normal and superfluid regimes by modulating the intensity of one of the trapping lasers .
They found that sound travelled at approximately the same speed , and with the same dispersion , regardless of the material ’ s state .
The measurement enables them to predict the speed of @ @ @ @ @ @ @ also thought to comprise strongly interacting Fermi gas , albeit with 25 orders of magnitude higher density .
Next , the researchers measured the diffusivity of the material , or how well it damps sound waves .
This quantity , which has never previously been measured in a strongly interacting Fermi gas , gives crucial information about the material : “ Total sound diffusivity has two components to it , ” explains Zwierlein , “ viscosity and thermal conductivity.
” Once again , the researchers found that there was no dramatic discontinuity in @ @ @ @ @ @ @ but instead it reached the lowest amount permitted : “ Even in the superfluid , you still have a quantum amount of friction , ” says Zwierlein , “ That is something I don ’ t think even many experts in my field realized.
” The team is now aiming to measure the thermal conductivity of the material directly , as well as looking into a bizarre phenomenon called “ second sound ” which occurs only in the superfluid phase .
Moreover , they anticipate that their results may provide fertile ground not @ @ @ @ @ @ @ and neutron stars but even for cosmologists .
This is because a split-second after the Big Bang , the universe is thought to have comprised a strongly interacting quark-gluon plasma : “ It turns out people predict very similar diffusivities to what we have if you replace the masses we have with the energies in the quark-gluon plasma , ” says Zwierlein .
Joseph Thywissen of the University of Toronto in Canada praises the high quality of the experiment : “ It ’ s a place in which new innovations in theory can @ @ @ @ @ @ @ “ You can ’ t hide behind a messy experiment or imperfections , because the experiment is near perfect…You ’ ve got to get the number right if your theory is right.
” John Thomas of North Carolina State University agrees , adding “ This new experiment on sound diffusivity is absolutely beautiful.
” Thomas ’ s own group have measured the viscosity dropping to zero below the superfluid transition temperature using a different technique – which is inconsistent with Zwierlein and colleagues ’ results .
“ There ’ s several different issues @ @ @ @ @ @ @ ’ s right and what ’ s really going on , ” he says : “ It ’ s not a trivial problem.
” The research is described in Science .

Good vibrations: artist’s concept of sound being transmitted in a fermionic superfluid. (Courtesy: Christine Daniloff/MIT)
The acoustic properties of an ultracold fermion gas have been measured either side of the superfluid transition temperature in an experiment that has been described as “near perfect” and “beautiful”. The results could have significant implications for understanding everything from superconductors to the aftermath of the Big Bang.
Superfluidity occurs at very low temperatures when bosons such as helium-4 form a single, macroscopic quantum ground state. As well as being able to flow indefinitely without losing kinetic energy, a superfluid can famously climb uphill over a barrier to reach an energy minimum. Some fermions such as helium-3 can also form a superfluid by first pairing up to form bosons.
In helium-3, the interactions between atoms are relatively weak. However, strongly interacting Fermi gases, in which the mean free path of the particles is barely longer than the spacing between them, can also become superfluids. These systems display markedly different properties from superfluid helium-3 and cannot be described by the standard theory of superfluidity developed by the Soviet physicist and Nobel laureate Lev Landau.
Extremely useful
Despite their strong interactions, these superfluids have lower viscosities than helium-3. “Landau’s paradigm just doesn’t work,” says Martin Zwierlein of Massachusetts Institute of Technology. Finding a theory that does, however, could be extremely useful because strongly interacting Fermi gases are widespread in physics. “Take, for example, the high temperature cuprate superconductors, in which electrons interact very strongly,” explains Zwierlein. “The resistance of these materials is very difficult or impossible to calculate theoretically, we do not understand these materials.”
One way to investigate any unfamiliar material, explains Zwierlein, is to tap it and listen to the resulting sound waves. “Hilariously, this had not been done,” he says, “because for 25 years we had been using focused laser traps that were grabbing onto the atoms, creating a very inhomogeneous soup which had high density in the centre and low density at the edges – it was not nice for such an experiment.”
In the new research, Zwierlein and colleagues built a “box trap” using three laser beams. “We shape light, roughly into the shape of a Coke can, and as this light is repulsive, whenever atoms hit the walls they bounce back into the box,” he says.
First, the researchers measured the speeds at which various acoustic waves propagated through the gas in both the normal and superfluid regimes by modulating the intensity of one of the trapping lasers. They found that sound travelled at approximately the same speed, and with the same dispersion, regardless of the material’s state. The measurement enables them to predict the speed of sound in neutron stars, which are also thought to comprise strongly interacting Fermi gas, albeit with 25 orders of magnitude higher density.
“Quantum amount of friction”
Next, the researchers measured the diffusivity of the material, or how well it damps sound waves. This quantity, which has never previously been measured in a strongly interacting Fermi gas, gives crucial information about the material: “Total sound diffusivity has two components to it,” explains Zwierlein, “viscosity and thermal conductivity.” Once again, the researchers found that there was no dramatic discontinuity in sound diffusivity at the superfluid transition, but instead it reached the lowest amount permitted: “Even in the superfluid, you still have a quantum amount of friction,” says Zwierlein, “That is something I don’t think even many experts in my field realized.”
The team is now aiming to measure the thermal conductivity of the material directly, as well as looking into a bizarre phenomenon called “second sound” which occurs only in the superfluid phase. Moreover, they anticipate that their results may provide fertile ground not only for those studying high temperature superconductors and neutron stars but even for cosmologists. This is because a split-second after the Big Bang, the universe is thought to have comprised a strongly interacting quark-gluon plasma: “It turns out people predict very similar diffusivities to what we have if you replace the masses we have with the energies in the quark-gluon plasma,” says Zwierlein.
Joseph Thywissen of the University of Toronto in Canada praises the high quality of the experiment: “It’s a place in which new innovations in theory can be tested,” he says, “You can’t hide behind a messy experiment or imperfections, because the experiment is near perfect…You’ve got to get the number right if your theory is right.”
John Thomas of North Carolina State University agrees, adding “This new experiment on sound diffusivity is absolutely beautiful.” Thomas’s own group have measured the viscosity dropping to zero below the superfluid transition temperature using a different technique – which is inconsistent with Zwierlein and colleagues’ results. “There’s several different issues in this that make it unclear who’s right and what’s really going on,” he says: “It’s not a trivial problem.”
The research is described in Science.


physicsworld--2020-12-04--Quantum tunnelling video bags teen $250,000 scholarship, how to win a horse race

The Canadian teenager Maryam Tsegaye has bagged a total of $ 400,000 in prizes for making the above video about quantum tunnelling .
Tsegaye , 17 , is winner of the 2020 Breakthrough Junior Challenge , which was founded by the billionaires Yuri and Julia Milner .
Tsegaye is a student at École McTavish Public High School in Fort MacMurray and her teacher Katherine Vladicka-Davies will get $ 50,000 of that prize money .
The school will get $ 100,000 for a new science lab and the remaining $ 250,000 goes to Tsegaye as a college scholarship .
“ Maryam @ @ @ @ @ @ @ of how to cleverly simplify a complex idea , and she provided a remarkable explanation of quantum tunnelling , ” says Scott Kelly , a retired NASA astronaut who was a prize judge .
Tsegaye says the win is a “ life-changing moment for me , and presents so many new opportunities that nothing will be the same from now on ” .
Enough left in the tank What is the ideal strategy to win a short-distance horse race – start off slow to conserve energy or go out hard and hope you @ @ @ @ @ @ @ a final kick ?
Mathematicians Quentin Mercier and Amandine Aftalion at the School for Advanced Studies in the Social Sciences ( EHESS ) in Paris have now attempted to answer that question by analysing the mathematics behind thoroughbred horseracing .
They used a GPS tracking tool placed under the jockey ’ s saddles at the Chantilly racetracks north of Paris to create a model of winning strategies at three different lengths on a looped track : 1300 m , 1900 m and 2100 m. The model even considered the aerobic and anaerobic energy @ @ @ @ @ @ @ slope and bend of the track .
Rather than holding the horses back for a strong finish , the researchers found that a strong start is a better strategy but keeping just in enough in reserve to provide a final kick to the finish line .
“ Information on a horse speed , endurance or running economy coupled with simulations can help to predict how a horse profile is adapted to some distances to run , ” the authors write , adding that “ to maximize an individual horse ’ s potential for @ @ @ @ @ @ @ races appropriate for its racing ability ” .
Their paper in PLOS One is called “ Optimal speed in Thoroughbred horse racing ” .

The Canadian teenager Maryam Tsegaye has bagged a total of $400,000 in prizes for making the above video about quantum tunnelling. Tsegaye, 17, is winner of the 2020 Breakthrough Junior Challenge, which was founded by the billionaires Yuri and Julia Milner. Tsegaye is a student at École McTavish Public High School in Fort MacMurray and her teacher Katherine Vladicka-Davies will get $50,000 of that prize money. The school will get $100,000 for a new science lab and the remaining $250,000 goes to Tsegaye as a college scholarship.
“Maryam’s video is a prime example of how to cleverly simplify a complex idea, and she provided a remarkable explanation of quantum tunnelling,” says Scott Kelly, a retired NASA astronaut who was a prize judge.
Tsegaye says the win is a “life-changing moment for me, and presents so many new opportunities that nothing will be the same from now on”.
Enough left in the tank
What is the ideal strategy to win a short-distance horse race – start off slow to conserve energy or go out hard and hope you have enough left in the tank for a final kick? Mathematicians Quentin Mercier and Amandine Aftalion at the School for Advanced Studies in the Social Sciences (EHESS) in Paris have now attempted to answer that question by analysing the mathematics behind thoroughbred horseracing.
They used a GPS tracking tool placed under the jockey’s saddles at the Chantilly racetracks north of Paris to create a model of winning strategies at three different lengths on a looped track: 1300 m, 1900 m and 2100 m. The model even considered the aerobic and anaerobic energy of the horses as well as the slope and bend of the track. Rather than holding the horses back for a strong finish, the researchers found that a strong start is a better strategy but keeping just in enough in reserve to provide a final kick to the finish line.
“Information on a horse speed, endurance or running economy coupled with simulations can help to predict how a horse profile is adapted to some distances to run,” the authors write, adding that “to maximize an individual horse’s potential for winning, it should be entered in races appropriate for its racing ability”.
Their paper in PLOS One is called “Optimal speed in Thoroughbred horse racing”.


physicsworld--2020-12-04--Chemical precursors to life could form in dark interstellar clouds

Some key molecular building blocks of life could have been created far earlier on in the formation of the solar system than previously thought .
Experiments and simulations done by Sergio Ioppolo at Queen Mary University of London and an international team have revealed how simple amino acids may have emerged via reactions on the surfaces of cold interstellar dust grains , long before the Sun first formed .
The discovery could transform our understanding of how life-forming compounds first arrived on the primordial Earth .
Ice contained within comets is thought to be some of the oldest and most @ @ @ @ @ @ @ By determining its composition , scientists can glimpse conditions present when comets first formed , alongside the Sun and the planets .
In 2014 , the ESA ’ s Rosetta probe arrived at the comet 67P/Churyumov-Gerasimenko and measured the chemical makeup of comet ice for the first time .
Rosetta found evidence for the amino acid glycine and its precursor methylamine in 67P ’ s coma of sublimated ice .
Both molecules are key building blocks of life on Earth .
Further investigation suggested that the molecules had become embedded in the pristine @ @ @ @ @ @ @ particles ejected from 67P , and had never been substantially altered by heat or liquid water at any point in the comet ’ s history .
At the time , modelling suggested that glycine and methylamine could have been created in the ice by exposure to radiation including cosmic rays and ultraviolet photons .
Now , however , Ioppolo ’ s team argue that this radiation would damage complex molecules after producing them .
In their study , the researchers looked at whether the molecules could have been made by “ non-energetic ” @ @ @ @ @ @ @ dark dust clouds that are characteristic of early star formation .
Through lab-based experiments , they recreated these conditions using bare dust grains coated in a water-rich ice layer , which they released inside an ultra-high vacuum chamber .
Even in such low-energy conditions , the chemistry observed by the team was surprisingly rich .
Within the ice a wealth of non-energetic reactions involving atoms and free radicals was observed .
This produced species including methane , ammonia , and carbon dioxide ; as well as the intermediate radicals required to produce glycine @ @ @ @ @ @ @ these processes further using astrochemical models .
This involved using laboratory data as a basis to extrapolate the chemical reactions which would likely take place in the next million years .
They calculated that glycine likely becomes abundant during the latter few 100,000s of years of evolution , as interstellar gas densities increase substantially .
Once formed , the glycine could then become a precursor to more complex amino acids , as functional groups are added to its backbone .
Eventually , ice-coated dust grains would coalesce into planetesimals like comets – which @ @ @ @ @ @ @ forming planets .
The research is described in Nature Astronomy .

Precursors of life: comet 67P/Churyumov-Gerasimenko as seen by Rosetta (Courtesy: ESA/Rosetta/NAVCAM, CC BY-SA IGO 3.0)
Some key molecular building blocks of life could have been created far earlier on in the formation of the solar system than previously thought. Experiments and simulations done by Sergio Ioppolo at Queen Mary University of London and an international team have revealed how simple amino acids may have emerged via reactions on the surfaces of cold interstellar dust grains, long before the Sun first formed. The discovery could transform our understanding of how life-forming compounds first arrived on the primordial Earth.
Ice contained within comets is thought to be some of the oldest and most pristine material in the solar system. By determining its composition, scientists can glimpse conditions present when comets first formed, alongside the Sun and the planets.
In 2014, the ESA’s Rosetta probe arrived at the comet 67P/Churyumov-Gerasimenko and measured the chemical makeup of comet ice for the first time. Rosetta found evidence for the amino acid glycine and its precursor methylamine in 67P’s coma of sublimated ice. Both molecules are key building blocks of life on Earth.
Ancient molecules
Further investigation suggested that the molecules had become embedded in the pristine water ice coating the surfaces of dust particles ejected from 67P, and had never been substantially altered by heat or liquid water at any point in the comet’s history.
At the time, modelling suggested that glycine and methylamine could have been created in the ice by exposure to radiation including cosmic rays and ultraviolet photons. Now, however, Ioppolo’s team argue that this radiation would damage complex molecules after producing them.
In their study, the researchers looked at whether the molecules could have been made by “non-energetic” reactions that occurred within the dense, dark dust clouds that are characteristic of early star formation. Through lab-based experiments, they recreated these conditions using bare dust grains coated in a water-rich ice layer, which they released inside an ultra-high vacuum chamber.
Intermediate radicals
Even in such low-energy conditions, the chemistry observed by the team was surprisingly rich. Within the ice a wealth of non-energetic reactions involving atoms and free radicals was observed. This produced species including methane, ammonia, and carbon dioxide; as well as the intermediate radicals required to produce glycine and methylamine.
The team then investigated these processes further using astrochemical models. This involved using laboratory data as a basis to extrapolate the chemical reactions which would likely take place in the next million years. They calculated that glycine likely becomes abundant during the latter few 100,000s of years of evolution, as interstellar gas densities increase substantially.
Once formed, the glycine could then become a precursor to more complex amino acids, as functional groups are added to its backbone. Eventually, ice-coated dust grains would coalesce into planetesimals like comets – which can deliver complex biological molecules to newly forming planets.
The research is described in Nature Astronomy.


physicsworld--2020-12-04--Dramatic footage emerges of Arecibo Observatory collapse

The Arecibo Observatory and the National Science Foundation ( NSF ) have released shocking footage of the moment earlier this @ @ @ @ @ platform collapsed onto the 305 m-wide dish .
The video was captured by a drone @ @ @ @ @ struck .
In a briefing along with the release of the footage , the NSF @ @ @ @ @ to mitigate environmental issues and finding a way to support the scientific community .
“ @ @ @ @ @ this loss to Puerto Rico and to so many that have called Arecibo their home @ @ @ @ @ week , ” noted Ashley Zauderer , NSF programme director for Arecibo .
“ It @ @ @ @ @ and it inspired scientific discovery .
”

The Arecibo Observatory and the National Science Foundation (NSF) have released shocking footage of the moment earlier this week when the 900 tonne platform collapsed onto the 305 m-wide dish.
The video was captured by a drone that was filming as disaster struck. In a briefing along with the release of the footage, the NSF said it is now working to mitigate environmental issues and finding a way to support the scientific community.
“We recognise the significance of this loss to Puerto Rico and to so many that have called Arecibo their home whether for years or a week,” noted Ashley Zauderer, NSF programme director for Arecibo. “It inspired schoolchildren and visitors, and it inspired scientific discovery.”


physicsworld--2020-12-04--‘Magnetic illusion’ can create magnetic fields at a distance

Physicists in the UK and Spain claim that they have found a way to generate and manipulate magnetic fields at a distance .
This opens up the possibility of projecting magnetic fields into inaccessible spaces and enables the remote cancellation of magnetic sources , the researchers say .
One application of this technique could be improving the control of magnetic microbots and nanoparticles within the human body , for medical applications such as drug delivery and magnetic hyperthermia therapies .
In recent years , metamaterials have enabled scientists to manipulate magnetic fields in unexpected ways , such as creating a @ @ @ @ @ @ @ magnetically undetectable and magnetic wormholes , which transport a magnetic field from one point in space to another .
In this latest work , published in Physical Review Letters , Rosa Mach-Batlle at the Universitat Autònoma de Barcelona and her colleagues wanted to see if they could generate a magnetic field that appears in free space , at a distance from its source .
Mach-Batlle tells Physics World that theory showed that to achieve this , they would need a magnetic material with negative permeability .
Magnetic permeability is the ability of a @ @ @ @ @ @ @ .
But there are no natural materials with negative permeability values .
Previously , the researchers had shown that a metamaterial with negative-permeability can be created by applying a precise arrangements of currents to the material .
This time , their theory showed that a long cylindrical tube with a magnetic permeability of −1 would act as a lens for electromagnetic waves .
If this cylinder was then placed around a magnetic source , the distribution of the magnetic field outside this shell would appear as if it had been created by another @ @ @ @ @ @ @ illusion – at a distance from the cylinder .
To create the metamaterial , the physicists used a 400 mm-long cylinder with a 40 mm radius .
With an arrangement of 20 wires , they controlled the surface current densities on its internal and external surfaces .
A wire running through the centre of the tube generated the magnetic field .
The researchers showed that with this set up they could create magnetic sources at a distance from the cylinder .
They also demonstrated that the metamaterial can be used to remotely cancel @ @ @ @ @ @ @ a wire with a current flowing through it at the point where they expected the projected magnetic field to appear .
The magnetic fields generated by the wire and the metamaterial cancelled each other out .
This technique could be used , the team say , to remotely cancel magnetic sources in inaccessible spaces , such as within a wall or inside a human body .
Mach-Batlle tells Physics World that it is worth noting that the magnetic field is not cancelled in all of the space .
“ There is a cylindrical @ @ @ @ @ @ @ that we cancel , ” she explains .
“ In this small region , the field is not cancelled , but in the rest of the space we would be cancelling the field of the source that we chose to cancel.
” The main practical application for this technique , Mach-Batlle believes , is not in cancelling magnetic sources , but in being able to create the illusion of a magnetic field at a distance inside inaccessible spaces .
This could have important implications in medicine , as it could be possible to @ @ @ @ @ @ @ .
If you create the illusion of a magnetic source inside the body , Mach-Batlle explains , you get a much stronger field compared with having the sources outside of the body .
This could be useful for the control and manipulation of nanoparticles for drug delivery and nanorobots that could be used for various types of surgery .
“ Also , in neuroscience , we think that it can have implications for transcranial magnetic simulation , ” Mach-Batlle says .
This technique for generating electric current at a specific area of the @ @ @ @ @ @ @ that has shown diagnostic and therapeutic potential in a number of neurological diseases and mental health conditions .

Magnetic illusion: a long wire surrounded by a magnetic replicator generates a replica of the wire outside it. (Courtesy: Phys. Rev. Lett. 10.1103/PhysRevLett.125.177204)
Physicists in the UK and Spain claim that they have found a way to generate and manipulate magnetic fields at a distance. This opens up the possibility of projecting magnetic fields into inaccessible spaces and enables the remote cancellation of magnetic sources, the researchers say. One application of this technique could be improving the control of magnetic microbots and nanoparticles within the human body, for medical applications such as drug delivery and magnetic hyperthermia therapies.
In recent years, metamaterials have enabled scientists to manipulate magnetic fields in unexpected ways, such as creating a magnetic cloak that can make an object magnetically undetectable and magnetic wormholes, which transport a magnetic field from one point in space to another.
In this latest work, published in Physical Review Letters, Rosa Mach-Batlle at the Universitat Autònoma de Barcelona and her colleagues wanted to see if they could generate a magnetic field that appears in free space, at a distance from its source.
Mach-Batlle tells Physics World that theory showed that to achieve this, they would need a magnetic material with negative permeability. Magnetic permeability is the ability of a material to acquire magnetization in magnetic fields. But there are no natural materials with negative permeability values.
Previously, the researchers had shown that a metamaterial with negative-permeability can be created by applying a precise arrangements of currents to the material. This time, their theory showed that a long cylindrical tube with a magnetic permeability of −1 would act as a lens for electromagnetic waves. If this cylinder was then placed around a magnetic source, the distribution of the magnetic field outside this shell would appear as if it had been created by another magnetic source – a kind of magnetic illusion – at a distance from the cylinder.
To create the metamaterial, the physicists used a 400 mm-long cylinder with a 40 mm radius. With an arrangement of 20 wires, they controlled the surface current densities on its internal and external surfaces. A wire running through the centre of the tube generated the magnetic field.
Calculated magnetic field distribution created by 20 current-carrying wires surrounding a centre wire (yellow dots) forming the replicator. The magnetic source created at a distance is seen in the shaded rectangle. (Courtesy: Phys. Rev. Lett. 10.1103/PhysRevLett.125.177204)
The researchers showed that with this set up they could create magnetic sources at a distance from the cylinder. They also demonstrated that the metamaterial can be used to remotely cancel another magnetic field, by setting up a wire with a current flowing through it at the point where they expected the projected magnetic field to appear. The magnetic fields generated by the wire and the metamaterial cancelled each other out. This technique could be used, the team say, to remotely cancel magnetic sources in inaccessible spaces, such as within a wall or inside a human body.
Mach-Batlle tells Physics World that it is worth noting that the magnetic field is not cancelled in all of the space. “There is a cylindrical region between our metamaterial and the source that we cancel,” she explains. “In this small region, the field is not cancelled, but in the rest of the space we would be cancelling the field of the source that we chose to cancel.”
The main practical application for this technique, Mach-Batlle believes, is not in cancelling magnetic sources, but in being able to create the illusion of a magnetic field at a distance inside inaccessible spaces. This could have important implications in medicine, as it could be possible to project a magnetic source inside the body.
If you create the illusion of a magnetic source inside the body, Mach-Batlle explains, you get a much stronger field compared with having the sources outside of the body. This could be useful for the control and manipulation of nanoparticles for drug delivery and nanorobots that could be used for various types of surgery.
“Also, in neuroscience, we think that it can have implications for transcranial magnetic simulation,” Mach-Batlle says. This technique for generating electric current at a specific area of the brain is an evolving area of research that has shown diagnostic and therapeutic potential in a number of neurological diseases and mental health conditions.


physicsworld--2020-12-03--Quantum advantage demonstrated using Gaussian boson sampling

A optical circuit has performed a quantum computation called “ Gaussian boson sampling ” ( GBS ) 100 trillion times faster than a supercomputer could , according to researchers in China .
This feat was achieved by Jian-Wei Pan and Chao-Yang Lu at the University of Science and Technology of China in Hefei , and colleagues .
Although GBS is devised to show that a quantum computation can be done much faster than the same calculation on a conventional computer – a capability called quantum advantage – it may also have specialized practical applications .
Boson sampling is a way @ @ @ @ @ @ @ optical circuit that has multiple inputs and multiple outputs .
Single photons enter the circuit in parallel and encounter optical components such as beam splitters .
Due to their bosonic nature , if two photons arrive at a beam splitter at the same time , they will both follow the same path .
This property makes it extremely difficult to use a conventional computer to calculate the output of the circuit even for modest numbers of input photons and output channels .
While boson sampling is difficult to do and requires state-of-the art @ @ @ @ @ @ @ even the most powerful supercomputers A Boson sampling circuit can be thought of as a matrix that makes a transformation of the input photons .
Calculating the output involves working out the “ permanent ” of the matrix , which is related to the determinant of the matrix but is much more difficult to calculate .
Boson sampling determines the permanent by sending groups of single photons into the optical circuit and measuring the output .
The number of photons is less than the number of output modes of the circuit – so @ @ @ @ @ @ @ six-mode circuit , for example .
In this latest research , the team used a related technique called Gaussian boson sampling ( GBS ) , in which single mode squeezed states of light are used in place of single photons .
Instead of determining the permanent of the circuit , Gaussian boson sampling gives a similar quantity that is also extremely difficult to compute using a conventional computer .
According to Pan , GBS offers two important advantages over the single-photon technique .
First is that the photon generation rate is much higher @ @ @ @ @ @ @ boson sampling , and second there are “ many proposals for practical applications based on [ GBS ] ” .
The team ’ s optical circuit has 100 inputs and 100 outputs and comprises 300 beam splitters and 75 mirrors that are arranged in a random manner .
The system is fully connected , so a photon at any input port can emerge from any of the output ports .
GBS took about 200 s to make the desired calculation , whereas the team estimate that China ’ s fastest supercomputer Sunway TaihuLight @ @ @ @ @ @ @ the calculation .
“ This experiment is definitely an important milestone for quantum simulations based on linear optical systems , ” says Christine Silberhorn at Paderborn University in Germany – who along with colleagues first proposed GBS in 2017 .
She points out that scaling-up the system to its 100×100 size would have been very challenging .
Ian Walmsley at Imperial College London agrees , adding that the team has made a “ heroic effort ” at “ preparing quantum states that are entirely indistinguishable , and making sure the photons aren ’ @ @ @ @ @ @ @ points out that use of bulk optics rather than integrated optics could make it difficult to further scale-up the system .
Undaunted , Lu says that the team has made a “ considerable improvement of the efficiency of the quantum light sources , ” which he says should enable a 144×144 version of the experiment .
Looking further ahead he says , “ In 2021 , we will make the GBS machine more tuneable , more compact and more stable , and look for practical applications ” .
Although the current system has @ @ @ @ @ @ @ Pan says , “ we are excited by the potential usefulness of boson sampling as the community has come up with many ideas ” .
Walmsley adds , “ There are some interesting simulation problems that might benefit from this new scale b boson sampler , including modelling of molecular spectra and vibrational dynamics .
However , even those require the addition of a deterministic nonlinearity at the single-photon level in order to be able to handle real-world systems accurately.
” The research is described in Science .

Quantum advantage: the Gaussian boson sampling experiment at the University of Science and Technology of China. (Courtesy: Chao-Yang Lu)
A optical circuit has performed a quantum computation called “Gaussian boson sampling” (GBS) 100 trillion times faster than a supercomputer could, according to researchers in China. This feat was achieved by Jian-Wei Pan and Chao-Yang Lu at the University of Science and Technology of China in Hefei, and colleagues. Although GBS is devised to show that a quantum computation can be done much faster than the same calculation on a conventional computer – a capability called quantum advantage – it may also have specialized practical applications.
Boson sampling is a way of computing the output of a linear optical circuit that has multiple inputs and multiple outputs. Single photons enter the circuit in parallel and encounter optical components such as beam splitters. Due to their bosonic nature, if two photons arrive at a beam splitter at the same time, they will both follow the same path. This property makes it extremely difficult to use a conventional computer to calculate the output of the circuit even for modest numbers of input photons and output channels. While boson sampling is difficult to do and requires state-of-the art quantum optics, it should vastly outperform even the most powerful supercomputers
A Boson sampling circuit can be thought of as a matrix that makes a transformation of the input photons. Calculating the output involves working out the “permanent” of the matrix, which is related to the determinant of the matrix but is much more difficult to calculate. Boson sampling determines the permanent by sending groups of single photons into the optical circuit and measuring the output. The number of photons is less than the number of output modes of the circuit – so three photons could be sent into a six-mode circuit, for example.
Single mode squeezed states
In this latest research, the team used a related technique called Gaussian boson sampling (GBS), in which single mode squeezed states of light are used in place of single photons. Instead of determining the permanent of the circuit, Gaussian boson sampling gives a similar quantity that is also extremely difficult to compute using a conventional computer.
According to Pan, GBS offers two important advantages over the single-photon technique. First is that the photon generation rate is much higher for GBS than it is for single-photon boson sampling, and second there are “many proposals for practical applications based on [GBS]”.
The team’s optical circuit has 100 inputs and 100 outputs and comprises 300 beam splitters and 75 mirrors that are arranged in a random manner. The system is fully connected, so a photon at any input port can emerge from any of the output ports.
GBS took about 200 s to make the desired calculation, whereas the team estimate that China’s fastest supercomputer Sunway TaihuLight would take 2.5 billion years to do the calculation.
“Important milestone”
“This experiment is definitely an important milestone for quantum simulations based on linear optical systems,” says Christine Silberhorn at Paderborn University in Germany – who along with colleagues first proposed GBS in 2017. She points out that scaling-up the system to its 100×100 size would have been very challenging.
Ian Walmsley at Imperial College London agrees, adding that the team has made a “heroic effort” at “preparing quantum states that are entirely indistinguishable, and making sure the photons aren’t lost”. However, he points out that use of bulk optics rather than integrated optics could make it difficult to further scale-up the system.
Undaunted, Lu says that the team has made a “considerable improvement of the efficiency of the quantum light sources,” which he says should enable a 144×144 version of the experiment. Looking further ahead he says, “In 2021, we will make the GBS machine more tuneable, more compact and more stable, and look for practical applications”.
Molecular spectra
Although the current system has no practical application beyond demonstrating quantum advantage Pan says, “we are excited by the potential usefulness of boson sampling as the community has come up with many ideas”.
Walmsley adds, “There are some interesting simulation problems that might benefit from this new scale b boson sampler, including modelling of molecular spectra and vibrational dynamics. However, even those require the addition of a deterministic nonlinearity at the single-photon level in order to be able to handle real-world systems accurately.”
The research is described in Science.


physicsworld--2020-12-03--Astronomers reveal most detailed atlas of the Milky Way

The European Space Agency ( ESA ) has released the latest star map of the Milky Way taken by its €450m Gaia mission .
Gaia ’ s third data set , released today , contains high-precision measurements of nearly 2 billion stars , allowing astronomers to trace the various populations of older and younger stars out towards the very edge of our galaxy – the so-called “ galactic anticenter ” .
The new data will also let scientists study how the solar system formed as well as its acceleration compared to the universe .
Gaia was launched in December 2013 @ @ @ @ @ @ @ its position around 1.5 million kilometres from Earth in the opposite direction from the Sun .
Gaia has two telescopes and the spacecraft rotates once every six hours so that they scan the sky , focusing light onto a huge CCD sensor with nearly a billion pixels – one of the largest ever flown in space .
Gaia ’ s mission is to plot the precise positions , motions , temperatures , luminosities and compositions of over a billion stars across the Milky Way .
The first data release , based on just @ @ @ @ @ @ @ published in 2016 and contained the distances and motions of two million stars that was followed by a second release in 2018 that covered the period between July 2014 and May 2016 .
This included high-precision measurements of nearly 1.7 billion stars as well as measurements of asteroids within our solar system .
The third data set comes in two parts , with today ’ s announcement being an early release of the full set , which is planned for 2022 .
“ The new Gaia data promise to be a treasure trove @ @ @ @ @ @ @ Bruijne , ESA ’ s Gaia deputy project scientist .

Sky mapper: new data from the Gaia mission is expected to be "treasure trove" for astronomers. (Courtesy: ESA/Gaia/DPAC; CC BY-SA 3.0 IGO/A. Moitinho)
The European Space Agency (ESA) has released the latest star map of the Milky Way taken by its €450m Gaia mission. Gaia’s third data set, released today, contains high-precision measurements of nearly 2 billion stars, allowing astronomers to trace the various populations of older and younger stars out towards the very edge of our galaxy – the so-called “galactic anticenter”. The new data will also let scientists study how the solar system formed as well as its acceleration compared to the universe.
Gaia was launched in December 2013 and started observations the following year from its position around 1.5 million kilometres from Earth in the opposite direction from the Sun. Gaia has two telescopes and the spacecraft rotates once every six hours so that they scan the sky, focusing light onto a huge CCD sensor with nearly a billion pixels – one of the largest ever flown in space. Gaia’s mission is to plot the precise positions, motions, temperatures, luminosities and compositions of over a billion stars across the Milky Way. Read more A billion pixels, a billion stars
The first data release, based on just over one year of observations, was published in 2016 and contained the distances and motions of two million stars that was followed by a second release in 2018 that covered the period between July 2014 and May 2016. This included high-precision measurements of nearly 1.7 billion stars as well as measurements of asteroids within our solar system.
The third data set comes in two parts, with today’s announcement being an early release of the full set, which is planned for 2022. “The new Gaia data promise to be a treasure trove for astronomers,” says Jos de Bruijne, ESA’s Gaia deputy project scientist.


physicsworld--2020-12-03--Durable perovskite solar cells

Durable perovskite solar cells

Available to watch now , The Electrochemical Society , in partnership with Hiden Analytical and the Royal Society of Chemistry @ @ @ @ @ instability issues of perovskite solar cells Dr Anita Ho-Baillie will start the talk with an @ @ @ @ @ followed by an outline of the instability issues of perovskite solar cells .
She will @ @ @ @ @ addressing these such as moisture instabilty .
The why and how perovskite solar cells become @ @ @ @ @ be discussed followed by our strategies of overcoming this .
Dr Anita Ho-Baillie research interest @ @ @ @ @ devices at nanoscale for integrating solar cells onto all kinds of surfaces generating clean energy @ @ @ @ @ Researcher ( 2019 ) , Dr Ho-Baillie is considered an international leader in advancing perovskite @ @ @ @ @ include setting solar-cell energy-efficiency world records in various categories .

Available to watch now, The Electrochemical Society, in partnership with Hiden Analytical and the Royal Society of Chemistry, explores the durability and instability issues of perovskite solar cells
Want to learn more on this subject? Watch now
Dr Anita Ho-Baillie will start the talk with an introduction of perovskite solar cells followed by an outline of the instability issues of perovskite solar cells. She will then move onto the strategies addressing these such as moisture instabilty. The why and how perovskite solar cells become unstable under thermal stress will be discussed followed by our strategies of overcoming this.
Want to learn more on this subject? Watch now
Dr Anita Ho-Baillie research interest is to engineer materials and devices at nanoscale for integrating solar cells onto all kinds of surfaces generating clean energy. A Clarivate Highly Cited Researcher (2019), Dr Ho-Baillie is considered an international leader in advancing perovskite solar cells. Her achievements include setting solar-cell energy-efficiency world records in various categories.


physicsworld--2020-12-03--Hot time for hard disks: why magnetic-recording technology is still going strong

When it comes to storing data , you might think that magnetic devices are rapidly becoming a thing of the past .
Surely solid-state drives are the future ?
But when I visited Queen ’ s University Belfast earlier this year , I was surprised to see lots of exciting R & D going on in magnetic storage .
My host was the physicist Robert Bowman , who works closely with Seagate Technology – one of the world ’ s largest manufacturers of magnetic storage devices and products .
Seagate is among the firms developing new approaches to magnetic storage @ @ @ @ @ @ @ quickly and with higher density than ever before .
Indeed , it sees no end in sight for the technology .
The market-intelligence firm IDC , for example , expects the amount of data stored in such devices to rise from 33 zettabytes ( 33 × 1021 bytes ) in 2018 to 175 zettabytes by 2025 .
If you stored that much information on Blu-ray discs , stacked together they would stretch 23 times the distance to the Moon .
In terms of cost and speed of access , magnetic storage wins hands @ @ @ @ @ @ @ were cheaper ( which it isn ’ t and probably never will be ) , there just isn ’ t enough fabrication capacity to physically build the storage we are projected to need in time .
Over 350 million hard disks are shipped every year and by 2029 the global market is expected to surpass $ 80bn globally .
Seagate ’ s technology facility in Northern Ireland alone makes almost 30 % of the global supply of read/write heads .
It ’ s incredible how far we ’ ve come in magnetic storage @ @ @ @ @ @ @ Smith first proposed storing audio in tiny metallic particles on a thread of cotton or silk .
Practical difficulties stopped Smith ’ s ideas in their tracks , but in 1928 the German-Austrian engineer Fritz Pfleumer developed the first magnetic tape recorder – an analogue device for storing sound .
Magnetic tape was first used for data storage in 1951 when the UNIVAC I computer was developed .
These days digital “ linear-tape ” cart-ridges are the cheapest form of storage , costing well below $ 0.01 per gigabyte .
They have an @ @ @ @ @ @ @ cartridges being able to cram 30 TB ( 30 × 1012 bytes ) of data – a figure that ’ s expected to grow to 40 TB by the end of the decade .
It ’ s a $ 5.8bn market that will rise to $ 6.5bn by 2026 according to market intelligence company PMR , partly driven by the need for offline back-ups and copies for disaster recovery and to counter the growing “ ransomware ” threat .
The trouble with tapes is that they ’ re linear strips , which means @ @ @ @ @ @ @ part to another .
That ’ s one reason why we have hard disks , which allow data to be accessed more quickly by jumping from one circular ring , or track , to another .
The first commercial computer to use a moving-head disk drive was IBM ’ s RAMAC 305 , produced in 1956 .
Containing 50 disks , each 24 inches in diameter , it offered 5 MB of storage , which was huge back then .
These days a hard disk has up to 20 TB of capacity , @ @ @ @ @ @ @ and fits in the palm of your hand .
Hard disks are marvels of physics and technological innovation .
Tiny read/write heads fly above their mirror-like surface ( itself a complex multi-layer ferromagnetic coating ) with a clearance of as little as 3 nm .
Operating in a humidity-controlled air- or helium-filled cavity , the height is controlled by an air bearing etched onto the head ’ s disk-facing surface and attached to a photo-etched precision-machined slider ( itself controlled by an ultra-precise stepper motor ) .
Each hard-disk track – of which @ @ @ @ @ @ @ – contains bits of information recorded into tiny areas just 42 nm wide ( roughly six to eight magnetic grains ) and 10 nm long ( barely two to three grains ) .
The disks rotate at speeds of up to 15,000 revs per minute ( as fast as the engine on a Formula 1 car ) while the read/write heads themselves are fabricated on 200 mm wafers using state-of-the-art photolithography and micro- and nano-fabrication processes .
Modern heads are based on tunnelling magnetoresistance ( a quantum effect linked to the 2007 Nobel @ @ @ @ @ @ @ advanced designs are being explored to increase the density further still .
Each hard disk also has multiple heads and multiple double-sided disks ( depending on the storage required ) , plus lots of precision-control electronics .
What a pity that most hard disks are encased in dull-looking metal boxes that live in thousands of dull‑looking “ cloud ” data centres around the world .
For me , a hard disk ’ s unique mix of semiconductor technologies , precision machining and ultra-precise stepper motors is a staggeringly impressive piece of engineering .
@ @ @ @ @ @ @ exist and you asked a team of engineers to design one from scratch – with a sub- $ 50 price tag – they ’ d think you were crazy and give you a thousand reasons why it couldn ’ t be done , not at any price .
Yet thanks to half a century of hard work and the power of incremental technological development , such devices do clearly exist .
And as Bowman explained , thanks to “ heat-assisted magnetic recording ” ( HAMR ) , Seagate has been able to increase @ @ @ @ @ @ @ to more than 2 TB per square inch , with the bits written via a laser and plasmonic near-field transducer integrated into the read/write head .
The firm will soon ship its first HAMR-based drives and Seagate is targeting 50 TB drives by 2026 .
So next time you check social media , browse the Web or look at a photo stored in the cloud , remember your data are on a hard disk on low-power standby , at a data centre somewhere in the world , waiting for your command .
The @ @ @ @ @ @ @ least humble things imaginable .

Physics World, where it appeared under the headline "Hot time for hard disks". Members of the Institute of Physics can enjoy the full issue Taken from the December 2020 issue of, where it appeared under the headline "Hot time for hard disks". Members of the Institute of Physics can enjoy the full issue via the Physics World app
James McKenzie looks at the power of incremental improvement and the commercial success of magnetic‑recording technology
Hot stuff Heat-assisted magnetic recording is set to boost the storage capacity of hard disks still further. (Courtesy: Seagate Technology)
When it comes to storing data, you might think that magnetic devices are rapidly becoming a thing of the past. Surely solid-state drives are the future? But when I visited Queen’s University Belfast earlier this year, I was surprised to see lots of exciting R&D going on in magnetic storage. My host was the physicist Robert Bowman, who works closely with Seagate Technology – one of the world’s largest manufacturers of magnetic storage devices and products.
Seagate is among the firms developing new approaches to magnetic storage to allow data to be stored more quickly and with higher density than ever before. Indeed, it sees no end in sight for the technology. The market-intelligence firm IDC, for example, expects the amount of data stored in such devices to rise from 33 zettabytes (33 × 1021 bytes) in 2018 to 175 zettabytes by 2025. If you stored that much information on Blu-ray discs, stacked together they would stretch 23 times the distance to the Moon.
Over 350 million hard disks are shipped every year and by 2029 the global market is expected to surpass $80bn globally.
In terms of cost and speed of access, magnetic storage wins hands down. And even if solid-state storage were cheaper (which it isn’t and probably never will be), there just isn’t enough fabrication capacity to physically build the storage we are projected to need in time. Over 350 million hard disks are shipped every year and by 2029 the global market is expected to surpass $80bn globally. Seagate’s technology facility in Northern Ireland alone makes almost 30% of the global supply of read/write heads.
Spinning a yarn
It’s incredible how far we’ve come in magnetic storage since 1888 when the US engineer Oberlin Smith first proposed storing audio in tiny metallic particles on a thread of cotton or silk. Practical difficulties stopped Smith’s ideas in their tracks, but in 1928 the German-Austrian engineer Fritz Pfleumer developed the first magnetic tape recorder – an analogue device for storing sound. Magnetic tape was first used for data storage in 1951 when the UNIVAC I computer was developed.
These days digital “linear-tape” cart-ridges are the cheapest form of storage, costing well below $0.01 per gigabyte. They have an immense storage capacity, with the latest cartridges being able to cram 30 TB (30 × 1012 bytes) of data – a figure that’s expected to grow to 40 TB by the end of the decade. It’s a $5.8bn market that will rise to $6.5bn by 2026 according to market intelligence company PMR, partly driven by the need for offline back-ups and copies for disaster recovery and to counter the growing “ransomware” threat.
Linear thinking
The trouble with tapes is that they’re linear strips, which means it takes time to go from one part to another. That’s one reason why we have hard disks, which allow data to be accessed more quickly by jumping from one circular ring, or track, to another. The first commercial computer to use a moving-head disk drive was IBM’s RAMAC 305, produced in 1956. Containing 50 disks, each 24 inches in diameter, it offered 5 MB of storage, which was huge back then. These days a hard disk has up to 20 TB of capacity, costs less than $0.02 per gigabyte and fits in the palm of your hand.
Hard disks are marvels of physics and technological innovation. Tiny read/write heads fly above their mirror-like surface (itself a complex multi-layer ferromagnetic coating) with a clearance of as little as 3 nm. Operating in a humidity-controlled air- or helium-filled cavity, the height is controlled by an air bearing etched onto the head’s disk-facing surface and attached to a photo-etched precision-machined slider (itself controlled by an ultra-precise stepper motor).
Each hard-disk track – of which there are about a million per inch – contains bits of information recorded into tiny areas just 42 nm wide (roughly six to eight magnetic grains) and 10 nm long (barely two to three grains). The disks rotate at speeds of up to 15,000 revs per minute (as fast as the engine on a Formula 1 car) while the read/write heads themselves are fabricated on 200 mm wafers using state-of-the-art photolithography and micro- and nano-fabrication processes.
A hard disk’s unique mix of semiconductor technologies, precision machining and ultra-precise stepper motors is a staggeringly impressive piece of engineering.
Modern heads are based on tunnelling magnetoresistance (a quantum effect linked to the 2007 Nobel Prize for Physics), but more advanced designs are being explored to increase the density further still. Each hard disk also has multiple heads and multiple double-sided disks (depending on the storage required), plus lots of precision-control electronics. What a pity that most hard disks are encased in dull-looking metal boxes that live in thousands of dull‑looking “cloud” data centres around the world.
For me, a hard disk’s unique mix of semiconductor technologies, precision machining and ultra-precise stepper motors is a staggeringly impressive piece of engineering. If modern hard disks didn’t exist and you asked a team of engineers to design one from scratch – with a sub-$50 price tag – they’d think you were crazy and give you a thousand reasons why it couldn’t be done, not at any price. Yet thanks to half a century of hard work and the power of incremental technological development, such devices do clearly exist.
A date with density
And as Bowman explained, thanks to “heat-assisted magnetic recording” (HAMR), Seagate has been able to increase the storage density of its hard disks to more than 2 TB per square inch, with the bits written via a laser and plasmonic near-field transducer integrated into the read/write head. The firm will soon ship its first HAMR-based drives and Seagate is targeting 50 TB drives by 2026. So next time you check social media, browse the Web or look at a photo stored in the cloud, remember your data are on a hard disk on low-power standby, at a data centre somewhere in the world, waiting for your command.
The humble hard disk is one of the least humble things imaginable.


physicsworld--2020-12-03--Stretchy cardiac implant measures and treats heart disease

Researchers from the University of Houston , the Texas Heart Institute and the University of Chicago have developed an implantable rubber patch that can collect information about the heart and use it to diagnose cardiac conditions .
Many cardiac devices , such as pacemakers , are limited in one of two ways .
They are either made using rigid materials and unable to conform to the complex surface of the heart , or they are flexible but limited in function .
This new device is made from fully rubbery materials and can be placed directly on the heart .
It @ @ @ @ @ @ @ beating heart .
This marks the first time that bioelectronics have been developed based on rubbery materials with similar mechanical properties to the tissues in the heart .
The device has several functions and can both collect information to diagnose conditions and carry out therapeutic functions .
It does not need an external power source as it uses energy collected from the beating of the heart .
The implant can monitor tissue strain and temperature , as well as measure electrophysiological activity , all of which are important factors that can help diagnose @ @ @ @ @ @ @ , this device can simultaneously collect this information from multiple regions across the heart to fully map the extent of any problem .
In addition to monitoring the heart , the device can also electrically pace it and perform thermal ablation to destroy damaged tissues .
The device itself is a thin elastic electronic sheet that is only 0.4 mm thick .
It is based entirely on rubbery materials , from the substrate to the semiconductors .
The main base of the device is PDMS ( polydimethylsiloxane ) , a common , low-cost @ @ @ @ @ @ @ bent , stretched and crumpled without suffering any damage .
In fact , it can be stretched by up to 30 % and still function .
As the mechanical properties of the implant are similar to those of cardiac tissue , the device can have a close interface with the heart , and the risk that the implant could damage the heart is reduced .
This device is not meant to be a long-term implant , but rather a temporary diagnostic measure .
With an extensive knowledge of how the heart is functioning @ @ @ @ @ @ @ cardiac disorders .
It could even help speed up the development of new treatments .
“ Unlike bioelectronics primarily based on rigid materials with mechanical structures that are stretchable on the macroscopic level , constructing bioelectronics out of materials with moduli matching those of the biological tissues suggests a promising route towards next-generational bioelectronics and biosensors that do not have a hard-soft interface for the heart and other organs , ” the researchers write .
Details of the implant are reported in Nature Electronics .

The flexible cardiac implant (left) and its potential location on the heart (right). (Courtesy: University of Houston)
Researchers from the University of Houston, the Texas Heart Institute and the University of Chicago have developed an implantable rubber patch that can collect information about the heart and use it to diagnose cardiac conditions.
Many cardiac devices, such as pacemakers, are limited in one of two ways. They are either made using rigid materials and unable to conform to the complex surface of the heart, or they are flexible but limited in function.
This new device is made from fully rubbery materials and can be placed directly on the heart. It can record data whilst bending with a beating heart. This marks the first time that bioelectronics have been developed based on rubbery materials with similar mechanical properties to the tissues in the heart.
Multifunctional implant
The device has several functions and can both collect information to diagnose conditions and carry out therapeutic functions. It does not need an external power source as it uses energy collected from the beating of the heart.
The implant can monitor tissue strain and temperature, as well as measure electrophysiological activity, all of which are important factors that can help diagnose a variety of heart conditions. Importantly, this device can simultaneously collect this information from multiple regions across the heart to fully map the extent of any problem. In addition to monitoring the heart, the device can also electrically pace it and perform thermal ablation to destroy damaged tissues.
The device itself is a thin elastic electronic sheet that is only 0.4 mm thick. It is based entirely on rubbery materials, from the substrate to the semiconductors. The main base of the device is PDMS (polydimethylsiloxane), a common, low-cost flexible material.
The device can be bent, stretched and crumpled without suffering any damage. In fact, it can be stretched by up to 30% and still function. As the mechanical properties of the implant are similar to those of cardiac tissue, the device can have a close interface with the heart, and the risk that the implant could damage the heart is reduced.
Flexible futures
This device is not meant to be a long-term implant, but rather a temporary diagnostic measure. With an extensive knowledge of how the heart is functioning, doctors can better diagnose and treat cardiac disorders. It could even help speed up the development of new treatments.
“Unlike bioelectronics primarily based on rigid materials with mechanical structures that are stretchable on the macroscopic level, constructing bioelectronics out of materials with moduli matching those of the biological tissues suggests a promising route towards next-generational bioelectronics and biosensors that do not have a hard-soft interface for the heart and other organs,” the researchers write.
Details of the implant are reported in Nature Electronics.


physicsworld--2020-12-02--Lightning ‘superbolts’ have a unique formation mechanism, satellite studies suggest

Superbolts – the rare and most extreme form of lightning — can be more than a thousand times brighter than regular lightning flashes and have a distinct formation mechanism – according to a new study done in the US .
As well as shining new light on the origins of this impressive phenomenon , this latest research could also help inform lightning safety efforts .
Superbolts were first reported in 1977 , following observations made by the satellite constellation of Project Vela , which was a US programme to monitor the globe for nuclear explosions .
Vela spotted flashes that @ @ @ @ @ @ @ than typical lightning and lasted about 1 ms. Superbolts were spotted across the globe , although more frequently over the North Pacific in regions of strong convective activity and in association with severe thunderstorms .
Since then , the superbolt mechanism and whether superbolts are a distinct form of lightning has remained a subject of debate .
One argument , for example , suggests that the detection of apparent superbolts by Vela and other satellites may simply be an artefact of these observatories having a good vantage point .
Normally when lightning is @ @ @ @ @ @ @ it appear dimmer than it would appear on the ground .
However , Michael Peterson , an atmospheric scientist at the Los Alamos National Laboratory in New Mexico points out that “ sometimes the satellite is in just the right place to see the source with little-to-no cloud in the way , and this causes the flash to appear brighter than normal .
This usually happens when the satellite is closer to the horizon and can see below the upper anvil cloud surrounding the storm core.
” In two new studies done at @ @ @ @ @ @ @ and Matt Kirkland analysed data collected by optical sensors aboard the Fast On-Orbit Detection of Transient Events ( FORTE ) and GOES-16 satellites to determine the brightness of superbolt events .
FORTE provided twelve years of lightning observations , while two years of data gathered by the Geostationary Lightning Mapper ( GLM ) aboard GOES-16 were analysed .
The GLM recorded 2,021,554 superbolt events with a magnitude of at least 100 times that of the average for regular lightning , while FORTE detected 20,283 .
The team found that the global distribution of @ @ @ @ @ @ @ regular lightning .
The most extreme events , however , had a unique distribution , with those seen by GLM ( which views the Americas ) concentrated over the central US and South America ’ s La Plata basin .
The team determined that the brightest superbolt events typically arise from rarer positively charged cloud-to-ground flashes , rather than the negatively charged phenomena that characterize most lightning .
“ There is a link between superbolts and high-current positive polarity strokes in the long horizontal lightning flashes that stretch for hundreds of kilometres known @ @ @ @ @ @ @ Peterson .
This is unlike regular lightning , which originates in the main , negatively charged region in the mid-levels of thunderstorms – and thus carries a net negative charge to the ground .
“ Positive-polarity lightning comes from a positive charge region .
The most prominent of these is usually located above the main negative charge region , so positive-polarity lightning tends to travel over longer distances to reach the ground , ” Peterson adds .
“ This is more difficult to do , and you often see this occur outside of @ @ @ @ @ @ @ as a bolt from the blue.
” The team often saw superbolts in clouds as part of larger flashes involving extensive networks of ionized lightning channels .
These networks move larger amounts of charge than normal and have more compact , lightning bolts .
They therefore produce considerably more intense optical emissions than normal lightning .
“ One lightning stroke even exceeded 3 TW of power – thousands of times stronger than ordinary lightning detected from space , ” notes Peterson .
“ Understanding these extreme events is important because it tells us @ @ @ @ @ @ @ Many of the [ superbolts ] occur over the oceans which deserves to be considered in lightning protection guidance , as the number of wind farms rapidly increases , ” observes Martin Fullekrug , a physicist at the University of Bath .
University of Washington physicist Robert Holzworth , meanwhile , is sceptical that “ true ” superbolts are only associated with positive charge events – which he notes disagrees with the findings of his previous work .
The Los Alamos work , he said , “ brings up the question about the @ @ @ @ @ @ @ systems , as compared to optical satellite systems .
I think this may be a red herring.
” Much remains to be learnt about superbolts , megaflashes and how lightning illuminates storm clouds in general .
Peterson says , “ We have only recently – in the past few years – started taking the continuous space-based measurements from geostationary orbit that permit these exceptionally-rare cases to be routinely identified , ” he explained .
“ The launch of the Meteosat Third Generation satellite next year will be an important milestone for space-based lightning @ @ @ @ @ @ @ hotspot region for lightning activity – the Congo Basin in Africa – and also a critical hotspot region for superbolts – the Mediterranean Sea.
” The research is described in two papers in the Journal of Geophysical Research : Atmospheres .

Tri-state area: this megaflash contained a superbolt that was 1000 times brighter than normal lightning. It was observed by the Geostationary Lightning Mapper and covers much of Tennessee, extending into Alabama and North Carolina.
Superbolts – the rare and most extreme form of lightning — can be more than a thousand times brighter than regular lightning flashes and have a distinct formation mechanism – according to a new study done in the US. As well as shining new light on the origins of this impressive phenomenon, this latest research could also help inform lightning safety efforts.
Superbolts were first reported in 1977, following observations made by the satellite constellation of Project Vela, which was a US programme to monitor the globe for nuclear explosions. Vela spotted flashes that were at least 100 times more intense than typical lightning and lasted about 1 ms. Superbolts were spotted across the globe, although more frequently over the North Pacific in regions of strong convective activity and in association with severe thunderstorms.
Since then, the superbolt mechanism and whether superbolts are a distinct form of lightning has remained a subject of debate. One argument, for example, suggests that the detection of apparent superbolts by Vela and other satellites may simply be an artefact of these observatories having a good vantage point.
Good views
Normally when lightning is viewed from space, cloud cover makes it appear dimmer than it would appear on the ground. However, Michael Peterson, an atmospheric scientist at the Los Alamos National Laboratory in New Mexico points out that “sometimes the satellite is in just the right place to see the source with little-to-no cloud in the way, and this causes the flash to appear brighter than normal. This usually happens when the satellite is closer to the horizon and can see below the upper anvil cloud surrounding the storm core.”
In two new studies done at Los Alamos, Peterson, Erin Lay and Matt Kirkland analysed data collected by optical sensors aboard the Fast On-Orbit Detection of Transient Events (FORTE) and GOES-16 satellites to determine the brightness of superbolt events. FORTE provided twelve years of lightning observations, while two years of data gathered by the Geostationary Lightning Mapper (GLM) aboard GOES-16 were analysed.
The GLM recorded 2,021,554 superbolt events with a magnitude of at least 100 times that of the average for regular lightning, while FORTE detected 20,283. The team found that the global distribution of the least radiant superbolts mirrored that of regular lightning. The most extreme events, however, had a unique distribution, with those seen by GLM (which views the Americas) concentrated over the central US and South America’s La Plata basin.
The team determined that the brightest superbolt events typically arise from rarer positively charged cloud-to-ground flashes, rather than the negatively charged phenomena that characterize most lightning. “There is a link between superbolts and high-current positive polarity strokes in the long horizontal lightning flashes that stretch for hundreds of kilometres known as ‘megaflashes’,” says Peterson. This is unlike regular lightning, which originates in the main, negatively charged region in the mid-levels of thunderstorms – and thus carries a net negative charge to the ground.
Bolt from the blue
“Positive-polarity lightning comes from a positive charge region. The most prominent of these is usually located above the main negative charge region, so positive-polarity lightning tends to travel over longer distances to reach the ground,” Peterson adds. “This is more difficult to do, and you often see this occur outside of the thunderstorm core where it can strike as a bolt from the blue.”
The team often saw superbolts in clouds as part of larger flashes involving extensive networks of ionized lightning channels. These networks move larger amounts of charge than normal and have more compact, lightning bolts. They therefore produce considerably more intense optical emissions than normal lightning.
“One lightning stroke even exceeded 3 TW of power – thousands of times stronger than ordinary lightning detected from space,” notes Peterson. “Understanding these extreme events is important because it tells us what lightning is capable of.”
Protecting wind farms
“Many of the [superbolts] occur over the oceans which deserves to be considered in lightning protection guidance, as the number of wind farms rapidly increases,” observes Martin Fullekrug, a physicist at the University of Bath.
University of Washington physicist Robert Holzworth, meanwhile, is sceptical that “true” superbolts are only associated with positive charge events – which he notes disagrees with the findings of his previous work. The Los Alamos work, he said, “brings up the question about the details of strong lightning detected by RF systems, as compared to optical satellite systems. I think this may be a red herring.”
Much remains to be learnt about superbolts, megaflashes and how lightning illuminates storm clouds in general. Peterson says, “We have only recently – in the past few years – started taking the continuous space-based measurements from geostationary orbit that permit these exceptionally-rare cases to be routinely identified,” he explained. “The launch of the Meteosat Third Generation satellite next year will be an important milestone for space-based lightning research because it will cover a key hotspot region for lightning activity – the Congo Basin in Africa – and also a critical hotspot region for superbolts – the Mediterranean Sea.”
The research is described in two papers in the Journal of Geophysical Research: Atmospheres.