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.”


  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:, 8 May 2017.


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.


  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

Silicon brings more colour to holograms

Silicon holograms harness the full visible spectrum to bring holographic projections one step closer

We can’t yet send holographic videos to Obi-Wan Kenobi on our droid, but A*STAR researchers have got us a little bit closer by creating holograms from an array of silicon structures that work throughout the visible spectrum1.

Many recent advances in hologram technology use reflected light to form an image; however the hologram made by Dong Zhaogang and Joel Yang from the A*STAR Institute of Materials Research and Engineering uses transmitted light. This means the image is not muddled up with the light source.

The team demonstrated the hologram of three flat images at wavelengths ranging from blue (480 nanometers) to red (680 nanometers). The images appeared in planes 50 microns apart for red and higher spacings for shorter wavelengths.

“In principle, it can be tuned to any wavelength,” says Yang.

Holograms can record three-dimensional images, which mean they can store large amounts of information in increasingly thin layers.

Recently, holograms that are mere hundredths of the thickness of a human hair have been made from metal deposited onto materials such as silicon. The holograms are created by nanoscale patterns of metal that generate electromagnetic waves that travel at the metal–silicon interface; a field called plasmonics.

Silicon holograms are slightly thicker than the metal-based ones, but have the advantage of being broadband. Plasmonic holograms only operate in the red wavelengths because they undergo strong absorption at blue wavelengths.

A disadvantage of the silicon holograms is their poor efficiency at only three per cent; however Dong estimates this could easily be tripled.

“The losses can be lowered by optimizing the growth method to grow polycrystalline silicon instead of amorphous silicon,” he says.

The hologram is an array of tiny silicon skyscrapers, 370 nanometers tall with footprints 190 nanometers by 100 nanometers. Unlike a city grid, however, the tiny towers are not laid out in neat squares but at varying angles.

The hologram operates with circularly polarized light, and the information is encoded on to the light beam by the varied angles of the skyscrapers. These alter the phase of the transmitted light through the ‘Pancharatnam–Berry effect’.

“What’s interesting about this hologram is that it controls only the phase of the light by varying the orientation of the silicon nanostructures. The amplitude is the same everywhere; in principle you can get a lot of light transmitted,” says Yang.

The A*STAR researchers focused on nanofabrication and measurements and collaborated with Cheng-Wei Qiu from National University of Singapore, whose team specializes in hologram design.

The A*STAR-affiliated researchers contributing to this research are from the Institute of Materials Research and Engineering and the Data Storage Institute


  1. Huang, K., Dong, Z., Mei, S., Zhang, L., Liu, Y. et al. Silicon multi-meta-holograms for the broadband visible light. Laser & Photonics Reviews 10, 500–509 (2016)| Article


Original on A*STAR journal website, published by Nature Group.

Shooting Star collides with star

I wrote this as a writing test in a job interview for CSIRO. Thought it was OK – but i didn’t get the job….


Have you ever wondered what would happen if a shooting star collided with a star? Well, scientists at CSIRO think they have discovered just that! Unfortunately the collision is too far away to see, but the scientists have discovered that Star PSR J0738-4042 is bombarded – regularly!

Shooting stars are actually pieces of spacerock that burn up as they fall into our atmosphere. Spacerocks are falling into PSR J0738-4042 as a result of it exploding in the past, flinging out debris that is now falling back in on itself.

In the explosion the star became a pulsar that shoots out radio waves as it spins, at nearly three turns per second. The falling debris gets zapped by the radio waves, turning it into plasma, which then affects the star’s regular pulses. By measuring changes in the pulses the scientists calculated the mass of one of the rocks at around a billion tonnes!


How twisting a belt explains the Universe

Quantum physics is all about the simplest things in the universe. Matter – electrons and quarks (which make up neutrons and protons), and interactions – photons, forces etc.

The difference between the two is a simple rotation. It’s secret quantum mechanics knowledge, says head of ANU Dept of Quantum Physics, Professor Craig Savage.

Here he is proving it:

Filmed at Physics in the Pub ACT, 2016, August 17 at Smiths Alternative Bookshop