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Metasurface Optics for Better Cellphone Cameras and 3-D Displays

Engineers at the California Institute of Technology have created a metasurface out of tiny pillars of silicon that act as waveguides for light. The way they arrange the pillars allows them to control the phase of light passing through the surface; this ability gives them control over how the light is focused, as well as its polarization, which is important for uses such as liquid crystal displays and 3-D glasses. Metasurfaces are structured planes so thin that they count as being two-dimensional; their periodic designs manipulate light in unusual ways.

“We're trying to create kind of a new platform for optics,” says Amir Arbabi, a postdoc in Andrei Faraon's Nanoscale and Quantum Optics Lab. The team described their work in the latest issue of Nature Nanotechnology.

The silicon pillars have to be somewhat shorter than the wavelength of light they're designed to manipulate. In the case of the metasurface described in the paper, the pillars are 715 nanometers tall, to handle infrared light with a wavelength of 915 nm. But they could easily be made shorter for visible light, Arbabi says. The pillars range in diameter from 65 to 455 nm, and they're elliptical in shape. The ellipses are not all oriented in the same direction; the pillars’ thickness and orientation determine how they focus and polarize the light passing through them.

Many of the same effects can be achieved with traditional optics, but that requires lining up multiple components such as lenses and prisms and beam splitters. The metasurface gets the job done with less bulk, allowing, among other things, thinner, lighter-weight cell phone camera lenses and better systems for directing the beams of industrial cutting lasers. It could also lead to novel applications. Using one of these devices, a display could switch between two polarizations and display two different holographic images. Or with an intermediate polarization, it could superimpose one image on the other. The metasruface could provide the optics for an LCD to create a 3-D display viewable from many angles without glasses.

What’s more, all of this can be done using the same lithography techniques used to build computer chips, doing away with individual fabrication and manual alignment of components. “We're trying to take these free-space components that are bulky and large and put them on a chip,” Arbabi says.

It shouldn't take much effort to move these metasurfaces from the lab to the marketplace, says Faraon. It's mainly a question of figuring out which optical system applications could benefit from the kind of mass production this technology makes possible. The array of potential applications is vast, Faraon says. “It gives you a unified framework, so you can design whatever optical component you would like.”


Say Hello to MIAOW, the First Open Source Graphics Processor

While open-source hardware is already available for CPUs, researchers from the Vertical Research Group at the University of Wisconsin-Madison have announced at the Hot Chips Event in Cupertino, Calif., that they have created the first open source general-purpose graphics processor (GPGPU). 

Called MIAOW, which stands for Many-core Integrated Accelerator Of the Waterdeep, the processor is a resistor-transistor logic implementation of AMD's open source Southern Islands instruction set architecture. The researchers published a white paper on the device. 

The creation of MIAOW is the latest in a series of steps meant to keep processor development in step with Moore's Law, explains computer scientist Karu Sankaralingham, who leads the Wisconsin research group. 

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Europe Mismanages 10 Times the Amount of E-Waste It Exports

Broken electronics shipped off to foreign shores can lead to environmental damage and health risks for scavenging workers. But a European Union-funded report has found that mismanagement and illegal trading of electronic waste within Europe itself can involve 10 times the amount of e-waste that ends up as undocumented exports to other countries.

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New Sensor Predicts Which Lung Transplants Will Fail

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With a tiny chip-based sensor and 30 minutes of time, surgeons could evaluate a lung destined for transplantation and predict whether that donated organ is likely to fail or whether it will save a life. 

In lung transplant surgery, the clock is ticking. Once surgeons remove the donor lung they have about 7 hours before it’s too damaged to be used, and transplant teams often rush the organ via helicopter to the hospital where a desperate recipient is waiting. People who need lung transplants are typically in the final stages of a lung disease such as emphysema or cystic fibrosis, and have exhausted all other treatment options. 

Sometimes, despite the doctors’ best efforts, the transplanted lung begins to malfunction in the recipient’s body. This disorder, called primary graft dysfunction, is the leading cause of death for patients in the immediate aftermath of surgery. 

The new sensor can predict, before transplantation, which donated lungs will malfunction. Biomedical engineer Shana Kelley and her colleagues at the University of Toronto created a tiny electrochemical device that detects several biomarkers associated with graft dysfunction, and can do so within half an hour. The researchers describe the experimental device in the journal Science


Their technical advance is the creation of a “fractal circuit sensor,” on which nanoscale gold particles form spiky lines along a glass chip. These protrusions increase the sensor’s surface area, and produce more accurate readings. On these gold electrodes are genetic “probes,” strands of DNA that register the presense of genetic biomarkers associated with graft dysfunction. For example, one probe indicates that the lung cells are producing interleukin-6, a molecule linked to the body’s inflammatory response. When the genetic probes detect and bind to their targets, the electrodes register a tiny change in voltage. 

This new tech is still far from real clinical use, but Kelley and her colleagues think it could offer a big improvement over current procedures. Today, transplant teams do basic checks of a donated lung’s viability, but they don’t have time to do sophisticated tests. Genetic tests of the lung tissue currently require “6 to 12 hours in a typical hospital workflow,” the researchers write, and they require highly trained personnel and contamination-free laboratories—which may not be available at the critical transplant moment.

The new sensor can do the same genetic testing in less than 30 minutes. In addition to preventing graft dyfunction by recognizing problematic lungs, the sensor could also be used to evaluate questionable lungs that are currently discarded out of an abundance of caution. “It is estimated that 40 percent of the discarded lungs may actually be suitable for clinical transplantation,” the researchers write. Salvaging those organs would be a great benefit, because a lung is a terrible thing to waste. 

How to Build a Space Elevator From Scratch

Even with innovations like SpaceX’s reusable robotic boosters, chemical rockets remain an expensive, dangerous and unreliable way to reach orbit. How much easier it would be if astronauts could simply step into an elevator, press O for Orbit, and ascend gracefully to outer space.

This is the dream of the collection of scientists, engineers, and entrepreneurs in the International Space Elevator Consortium (ISEC) who got together for its annual conference last week in Seattle.

The idea of a space elevator has been around for over a century. The basic concept is simple: a tether descends from a spacecraft in geostationary orbit to a floating platform at the equator, probably in the eastern Pacific Ocean. Because of a counterweight that would extend far into space, the space elevator’s tether would be gravitationally stable, allowing electric elevator cars to make the week-long climb to orbit powered by solar panels and ground-based lasers.

Such a system, ISEC researchers believe, could eventually slash the cost of raising a kilogram of payload into geosynchronous orbit from roughly US $25,000 to $300 or less. The key word, of course, is “eventually.” Technical challenges are legion, including building the aircraft carrier–size floating platform, designing safe, speedy climbers, and avoiding space debris and other satellites. But the truly fundamental obstacle is the lack of a material strong and resilient enough to form the elevator’s tether.

In current designs, the space elevator’s tether is not a thick round cable as originally proposed, but a paper-thin ribbon, a meter wide and 100,000 kilometers long. Even with such a slimmed-down approach, the strain of simply keeping its own mass aloft would instantly shred any tether made from steel, Kevlar, carbon composites, or even the best carbon nanotubes we can currently make.

In the ISEC conference’s keynote address, Mark Haase, a materials engineer from the University of Cincinnati, talked about how a tether at least ten times stronger than anything existing today might be made. His idea started with carbon nanotubes, which still hold tremendous promise for the manufacturing of superstrong materials. Discovered in 1991, carbon nanotubes are cylindrical structures formed by sheets of single carbon atoms. They are already being manufactured in bulk, mostly as an additive to other materials in order to boost their strength and thermal or electrical conductivity.

But while individual carbon nanotubes can be immensely strong, they are awkward to tease into macroscopic-scale objects. They can’t be melted and extruded like Kevlar, nor sorted and aligned like natural fibers. The longest carbon nanotube made so far, if stood on its end, would barely reach a child’s knee, let alone one-quarter of the way to the Moon. Haase believes that the way forward is to cross-link nanotube molecules using minuscule amounts of polymer glue.

ISEC is not putting all of its eggs in a basket made from carbon nanotubes, however. Graphene, a single-atom-thick sheet of carbon, is also a promising material, although it does not respond as well as nanotubes to the kind of twisting and bending that a 100,000-km-long tether moving back and forth through the atmosphere would certainly experience.

More exotic still are boron nitride nanotubes. Similar in form to carbon nanotubes but made up of alternating boron and nitrogen atoms, this ceramic is incredibly chemically stable. That quality should help it survive long periods situated high in Earth’s atmosphere where highly reactive atomic oxygen would likely degrade a carbon nanotube tether. (Engineers on the nanotube track say they have devised a solution to this cosmic erosion: a gold coating for vulnerable sections of the tether.) Boron nitride nanotubes could also cope well with solar and cosmic radiation beyond the magnetosphere.

“As we gain more knowledge about these materials, we have a real chance to improve strengths,” says Haase. He predicts that the most promising candidates, nanotube-polymer composites, will reach the minimum strength needed for a space elevator tether “in about 20 years.”

Bryan Laubscher, a director at ISEC, believes that the search for a tether material will have an impact long before then. Laubscher, who left his job as an engineer at Lockheed Martin in 2010 to form a company developing high strength materials for use in aviation and space applications, says, “Imagine a Boeing 797 made from carbon nanotubes. It would have one-tenth of the mass of today’s aircraft, and an airframe that won’t come apart in a crash.” 

In fact, ISEC is relying on the private sector for every dime of the space elevator’s estimated $18 billion price-tag. In a position paper published earlier this year, ISEC noted, “To this point, we have found no needed capability within the government that must be incorporated in the space elevator architecture.”

That might be a swipe at NASA, which in 2012 abandoned a $2 million competition aimed at creating ultra-strong tether materials. But when even the world’s richest and most visionary space agency can’t help with your moonshot, you might want to at least consider that your lofty ambitions for a space elevator seem destined to stay firmly on the ground floor.

Developmental Gaming System for Autistic Children

To help children with autistic spectrum disorder improve their social skills, researchers from the University of Kentucky have developed a prototype of a social narrative and gaming system, called MEBook.

A Microsoft Kinect camera wired to a PC tracks a child’s facial expressions, body movements and other behavioral patterns. The system’s current instantiation uses video self-modeling (VSM), an evidence-based approach in which kids watch videos of themselves successfully performing social behaviors, such as waving or smiling, during the intervention. Video footage of the successful moments are spliced together and reviewed with the child afterward. Researchers hope to release a free, downloadable version of MEBook for parents to use at home by the end of this year.

“The incorporation of the gaming system encourages the child to practice what s/he has learned in the social narrative by rewarding the correct behaviors with points and praises,” says Sen-ching Samson Cheung, an associate professor of electrical and computer engineering at the University of Kentucky.

Inspired by his own son’s autism spectrum disorder, Cheung is leading this project and searching for ways to help others affected by the same disorder. “Since his diagnosis six years ago, I have been thinking of different ways to apply my research to improve autism diagnosis and interventions,” he says.

The problem with teaching autistic children using social narratives such as animated stories illustrating social situations, Cheung says, is that kids on the autism spectrum have difficulty relating the social behavior in fictitious scenarios to those that occur in real life. The researchers believe that showing “real” videos of the child himself, as the main character, performing precise behavioral patterns, will help him or her relate those patterns to real life. Eventually, this helps the child build confidence for similar social environments.

Nkiruka Uzuegbunam, a Ph.D. student collaborating with Cheung on this project, talks about the system in the video below.

The system uses computer vision and signal processing algorithms to separate the subject from the background and to identify when certain behaviors emerge. Some of these algorithms are based on the researchers’ previous work, in which a video surveillance system protected the privacy of certain individuals by detecting them and erasing them from the video footage.

Cheung says they’ve already finished a preliminary clinical study utilizing the prototype system with three autistic children. “The results are very encouraging; all of our subjects showed an increase of social greeting skills after the intervention,” he says. His team is currently summarizing the results for an IEEE journal.

His team of collaborators in education, psychology, and medicine are also in the early alpha stage of developing a virtual-mirror system. They are looking to start clinical studies on it in 2016. With that system, the child’s behavior is captured and modified in real-time, and the image is rendered on a mirror-like display. This is part of a four-year NSF grant to apply advanced multimedia technology to enhance “self-model and mirror feedback imageries” for behavior therapies for children with autism.

Electric Glue Can Set Anywhere

Glue is playing an increasingly important role in manufacturing and technology—for example, in cars and airplanes, new and lighter materials, such as carbon composites and plastics are now an important constituant. And with such material, instead of bolts, screws and welds to hold things together, manufacturers are increasingly using high-quality glues.

The glues most of us are familier with are hardened and become adhesive by chemical means.  For example superglue hardens due to a chemical interaction with the water vapour in air.  Other ways glues rely on chemical changes induced by heat or  light.  However, these glues usually  don't work in wet environments:  Superglue will preferentially stick to water molecules instead of solid surfaces, for example.

Now a research group led by chemist Terry Steele at Nanyang Technological University (NTU) in Singapore has developed a glue that  hardens when a low voltage is applied to it.  They recently reported their research with the new adhesive, nicknamed “Voltaglue,” in Nature Communications.

“We had to find a way to make glue which cures (hardens) when we want it to without being affected by environmental conditions, so electricity was the best approach for us. The hardness of our glue can be adjusted by the amount of time we apply a voltage to it, which we call electrocuring,” says Steele in a NTU press release.

Steele cited two applications that highlighted the advantage of a glue whose hardness was easily adjustable: joining materials immersed in water or replacing sutures during surgery in human tissue. “For example, if we are gluing metal panels underwater, we want it hard enough to stick for a long time. However, for medical applications we want the glue to be more rubber-like so it wouldn’t cause any damage to the surrounding soft tissues,”  Steele also says  in the press release

The glue consists of a layer of hydrogel, a water based gel into which are dissolved carbon molecules called carbenes that are attached to plastic dendrimers, which are typically spherical large molecules.  Using electrodes to apply two volts across the glue causes the carbenes to start bonding with other dendrimers and nearby surfaces.  Once the voltage is removed, the bonding activity stops. 

The researchers have patented Voltaglue through NTUitive, NTU's innovation and enterprise company.

The new glue may also make recycling easier.  Cars could be designed in such a way that their components could become unglued and so more easily dissassembled.  Steele and his colleagues are now researching ways to make the action of the glue reversible by, for example, changing the polarity of the applied voltage.  

Estimate: Human Brain 30 Times Faster than Best Supercomputers

An artificial intelligence project recently funded by Silicon Valley pioneer Elon Musk aims to find a new way to compare supercomputers to the human brain. Instead of trying measure how quickly wetware or hardware can do calculations, the project measures how quickly the brain or a computer can send communication messages within its own network. That benchmark could provide a useful way of measuring AI’s progress toward a level comparable with human intelligence.

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Li-Fi in the ER

Imagine if you could eliminate the tangle of wires that snake across a hospital patient’s body so machines can monitor his or her vital signs. Sounds like a great idea. But wirelessly transmitting data from the patient to the machines cluttering hospital rooms creates the risk of electromagnetic interference. So one group of researchers in South Korea is proposing that some machines use Li-Fi instead.

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Gigantic Antarctic Instrument, IceCube, Finds Mysterious Cosmic Neutrinos

In a research published last week in Physical Review Letters, an Antarctic detector has managed to confirm the existence of a small handful of cosmic neutrinos: ultra high energy particles that likely originated from unknown sources far outside of our galaxy. These particles are nearly impossible to detect—it took a specially designed system of sensors burried in a cubic kilometer of ice. But the few we've seen have energies up to a thousand times greater than what the Large Hadron Collider can generate, and we're just starting to be able to get a sense of where they might be coming from.

(Go here for the incredible story of the engineering of the detector, called IceCube.)

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