Superconductors – the magic of meissner effect

 

Some lovely footage of superconductors weaving their magical levitation spell

One from the archives from Eurofusion.

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Space technology for a world of problems

The benefits of satellites are far-reaching and versatile. They can improve productivity on farms, locate people stranded in disaster zones, and even track sports performance.

Naohiko Kohtake’s research area of space once seemed among the least practical realms. But his work solves real-world problems for everyday people working on the land, looking for safety, or scoring their next try.

Kohtake is a system design scientist at Keio University, who thinks big about how satellites can collect, analyze, and even send out data. “The key is a holistic view,” says Kohtake, who is also an adjunct associate professor at the School of Engineering, Asian Institute of Technology. “Many people focus on specific areas, but we focus on optimization, system thinking, and modeling to design a sophisticated, merged system.”

A striking example of this is Kohtake’s disaster management systems. He has used location data collected from mobile phones and taxi GPS to analyze how people behave during disasters across Asia, such as the 2011 Tohoku earthquake and resulting tsunami. “Data is useful for finding social issues,” he says. “We can understand the program underneath — the human mind.”

While developing these systems, Kohtake realized that satellites could also help with communication in the confusion of a natural catastrophe. “After a disaster it is difficult to maintain contact and communicate messages to people,” he says.

Taking advantage of the fact that Japanese navigation satellites can broadcast messages directly to the GPS receiver built into mobile phones, Kohtake and students designed an app to get location information about designated meeting points or safe routes to people in disaster zones. Already, the system has been successfully trialed for bushfires in Australia and for tsunami warnings in several Asian countries.

This example, like many of Kohtake’s diverse research areas, grew out of his passion to broaden the uses of satellite data.

“Nearly every university has a program on how to build rockets and satellites, but few have courses on how to use satellite technology,” he says. To address this, Kohtake leads the Geospatial and Space Technology Consortium for Innovative Social Services (GESTISS), a collaboration set up in 2012 between several universities in Asia, including Keio University’s Graduate School of System Design and Management. Every year, GESTISS organizes tutorials, seminars and summer camps for 100 students across Asia and inspires them to think about how to employ satellites for social good.

Kohtake’s GESTISS students, in collaboration with Malaysian researchers, traveled to palm plantations in Malaysia, where they revolutionized the labor-intensive planting practices. Using satellite and drone data to create three-dimensional maps, they developed an app that enables a single person to calculate the optimal planting position — far more efficient than the traditional team method using long wires.

A team of students trained by Naohiko Kohtake have used satellite and drone data to improve the productivity of palm farmers in Malaysia.

 A team of students trained by Naohiko Kohtake have used satellite and drone data to improve the productivity of palm farmers in Malaysia.

© Naohiko Kohtake, Keio University

As well as rural settings, Kohtake is working in the most densely populated areas of the world. The obstacle of tall buildings can cause errors in navigation systems of several meters, which could lead to disaster for driverless cars. Kohtake’s solution is to develop a navigation app that uses data from multiple satellite networks — the Japanese Quasi-Zenith Satellite System, the Chinese BeiDou and the United States Global Positioning System (GPS) — and is accurate to within a meter.

Kohtake’s positioning system is so precise that he is now using it to benefit his favorite pastime, rugby. Each player is equipped with a small tracking device, enabling them to download a record of their every movement on the field, to analyze and improve their performance.

Wearable sensor technology (black vests) can be used to track a player's movement on the field.

Wearable sensor technology (black vests) can be used to track a player’s movement on the field.

© Keio University Rugby Football Club

This revolution in sport science, believes Kohtake, who is an adviser at the Japan Sport Council, will also give professionals a career path when they retire from sport.

“Top athletes interested in their performance data develop analytical skills, which are good not only for sport but also can help them move to other domains.”

References

  1. Choy, S. et al. Application of satellite navigation system for emergency warning and alerting. Computers, Environment and Urban Systems. 58, 12–18 (2016). | article
  2. Okami, S. & Kohtake, N. Fine-scale mapping by spatial risk distribution modeling for regional malaria endemicity and its implications under the low-to-moderate transmission setting in western Cambodia. 11, PLOS ONE e0158737 (2016). | article

A new spin on data storage

Seems physicists are inventing particles faster’n I can write about em. Who ever knew you could call a twisted magnetic field a particle?

First published here: http://www.research.a-star.edu.sg/research/7691/a-new-spin-on-data-storage, 8 May 2017.

2skyrmions

Magnetic field patterns in two types of skyrmions (Wikimedia)

Study into spirals of magnetic spin showcases potential of layered materials for future data storage

Tiny spirals of magnetism called skyrmions could be used as ultrahigh density energy-efficient data carriers.

Jarvis Loh, Gan Chee Kwan and Khoo Khoong Hong from the A*STAR Institute of High Performance Computing have modeled these minute spin spirals in nanoscopic crystal layers. They found that alternating layers of manganese silicide (MnSi) and cobalt silicide (CoSi) forms a promising material architecture.

“Skyrmions are nanosized entities, only tens of nanometers, so they hold the promise of higher storage density than the current technology,” said Gan.

Storage based on skyrmions would represent binary data such as ‘1’s and ‘0’s as clockwise and anticlockwise spin spirals, respectively. Skyrmions can improve energy efficiency as they can be created and manipulated with currents significantly smaller than those required for conventional magnetic hard disk technology.

Skyrmions had been experimentally observed in manganese silicide, prompting the team to explore simulations of manganese silicide in its pristine form and in combination with similar materials.

The team selected cobalt silicide because cobalt sits close to manganese in the periodic table, and its similar lattice characteristics mean it should combine well with manganese silicide. Cobalt also has strong magnetic properties — it is ferromagnetic.

The team’s simulations showed that coupling cobalt silicide to manganese silicide enables the spin spirals in manganese silicide to be engineered. “What’s interesting is that we can now vary the size of skyrmions in an easy and elegant way,” Loh said.

In the skyrmion’s center the magnetic spin of the atoms is flipped 180 degrees relative to the spin on its outside edge; between the edge and the center the spins progressively tilt between the two extremes. Critical in the size of skyrmions is the ability of the material to support high relative tilt between neighboring atoms in the lattice, which enables the skyrmion to be packed into a smaller spiral.

The team found that adding cobalt silicide layers to the manganese silicide layers increased the possible relative tilt. However there is an upper limit — for cobalt silicide layers double the thickness of the manganese silicide, the material ceased to support skyrmions and transitioned to a more conventional ferromagnetic behavior.

One of the attractions of skyrmions as a data storage medium is their robustness, says Loh. “Unlike current magnetic storage, skyrmions are resistant to defects in the lattice. They are topologically protected.”

The team plans to apply their successful approach to other potential architectures, such as nanowires.

The A*STAR-affiliated researchers contributing to this research are from the Institute of High Performance Computing.

Reference

  1. Loh, G. C., Khoo, K. H. & Gan, C. K. Helimagnetic order in bulk MnSi and CoSi/MnSi superlattices Journal of Magnetism and Magnetic Materials 421, 31–38 (2017). | Article

A magic cloak of earthquake protection

 

The editor thought Harry Potter was so last decade, so this Cosmos article got majorly changed.  Thought the original wasn’t bad though…

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Harry Potter’ invisibility cloak might just have been trumped by a French team, who aim to make entire buildings invisible. Scientists from the Institut Fresnel in Marseilles are teaming up with geo-engineering company Ménard for an experiment in the shape of a circle, two hundred metres across – enough to protect the whole of Hogwarts School (or more realistically a sensitive site such as a nuclear plant).

The team are not striving for invisibility to human eyes: instead of light waves they will divert the waves that travel through the surface of the earth during earthquakes and other seismic disturbances. As they reported in last month’s Physics Review Letters they have already succeeded with an area the size of Harry Potter’s Gryffindor common room.

“We managed to stop the propagation of the waves,” says the leader of the team, physicist Sebastien Guenneau. “This is the first proof of concept of a seismic metamaterial, a structure which can scatter and deflect wave trajectories. You can build on this knowledge to create an invisibility cloak which will actually protect a specific site from seismic waves.”

Metamaterials were first developed in the optics domain. They are substances comprised of an array of small elements, whose regular pattern leads to unusual behaviour on a large scale. Guenneau studied at Imperial College London with the pioneer of metamaterials, Sir John Pendry; Pendry shook the optics world in the early 2000s when he proposed an invisibility cloak based on metamaterials, and then, in collaboration with David Smith from Duke University, built such a device that operated at microwave wavelengths.

The strange effects that metamaterials have on waves rely on geometric structures that are smaller than the waves they are influencing. For Pendry’s centimeter-scale microwaves the patterns were millimetres in size,  but for Guenneau’s team, dealing with earthquake wavelengths of around a metre and a half, the structures were 30cm wide boreholes, spaced roughly a metre apart.

However, unlike metamaterials based on pure, man-made substances, the earth is much less homogeneous.

“Soil is a different story,” says Guenneau. “Its properties are difficult to characterise, and depend on different things, such as the weather! It makes the mathematical models much more difficult.”

Overcoming more than just mathematical hurdles – other scientists initially ridiculed the theory – Guenneau fortuitously met geo-engineer at Ménard, Stephane Brûlé, who was open minded and influential enough to persuade his company to collaborate on the idea – albeit during the summer holiday period.

So it was that the team of twenty people studied the weather forecasts carefully and chose three sunny days in August 2012, to take the measurements at a site near Grenoble.

Using a seismic source vibrating the ground at 50 times a second they first measured the propagation of the waves in the undisturbed soil. Then after carefully drilling three rows of five metre deep holes, they repeated the experiment. Sure enough, as the model predicted, most of the energy was reflected by the hole pattern; behind the array the detectors only measured one fifth of the energy that had reached the detector before the holes were drilled.

“It’s interesting because these are the first experimental results on this topic,” says University of Sydney physicist, Professor Boris Kuhlmey, who studies electromagnetic metamaterials that function at the nanometer wavelengths of light. “It’s the very beginning of the field: the modelling is quite extensive, but the experiment is quite limited in scope. The structure they have explored will only work over a narrow band of frequencies, but if your aim is to stop an earthquake you don’t get to choose the frequency.”

However Kuhlmey says Guenneau’s mathematical models offer the possibility of a phenomenon known as a zero stop band, which can cut out a wide range of earthquake waves. “These exist in electromagnetic metamaterials – the paper suggests that for seismic waves they are possible too. That would be really key to get it to work well. Maybe it’s possible, on the scale of a city, to diminish the impact of an earthquake considerably.”

Guenneau’s next experiment will certainly push back the boundaries. The team will inflict earthquakes measuring six on the Richter scale, with frequencies of between 2 and 12 vibrations per second on their test site, protected by a ring of boreholes 200 metres in diameter.

“It would be a dream for me to see this done for real one day, not just tests,” muses Guenneau. But he is not precious about his idea. “I am sure that the civil engineers will come up with better ways to make it work, I don’t have the expertise,” he says.

In the meantime he is already turning his considerable skills to other problems, such as tsunami control. “Imagine some columns of wood, 200 m from the sea shore, arranged in a similar fashion to the bore holes in the seismic experiments. The effect will be that you deflect or guide the tsunami to a nonsensitive coastal area.”

“Also, I’d like to do some work in biology…” he throws in.


Originally published in Cosmos Magazine 28/4/14