System Bits: May 15

Navigating with GPS and sensors
According to MIT Computer Science and Artificial Intelligence Laboratory (CSAIL) researchers, navigating roads less traveled in self-driving cars is a difficult task mainly because self-driving cars are usually only tested in major cities where countless hours have been spent meticulously labeling the exact 3D positions of lanes, curbs, off-ramps, and stop signs.

MapLite uses perception sensors to plan a safe path, including LIDAR to determine the approximate location of the edges of the road.

Source: MIT

Daniela Rus, director of CSAIL said, “The cars use these maps to know where they are and what to do in the presence of new obstacles like pedestrians and other cars. The need for dense 3D maps limits the places where self-driving cars can operate.”

Further, the millions of miles of U.S. roads that are unpaved, unlit, or unreliably marked are often much more complicated to map, and get a lot less traffic, so companies aren’t incentivized to develop 3D maps for them anytime soon meaning that there are huge swaths of America that self-driving cars simply aren’t ready for.

One way around this is to create systems advanced enough to navigate without these maps, therefore Rus and her team at CSAIL have developed MapLite, a framework that allows self-driving cars to drive on roads they’ve never been on before without 3D maps.

MapLite combines simple GPS data that is found on Google Maps with a series of sensors that observe the road conditions. Together, these elements allowed the team to autonomously drive on multiple unpaved country roads in Devens, Massachusetts, and reliably detect the road more than 100 feet in advance.

CSAIL graduate student Teddy Ort, who was a lead author on a related paper about the system said the reason this kind of ‘map-less’ approach hasn’t really been done before is because it is generally much harder to reach the same accuracy and reliability as with detailed maps. “A system like this that can navigate just with on-board sensors shows the potential of self-driving cars being able to actually handle roads beyond the small number that tech companies have mapped.”

Theory for one type of superconductor solves puzzle in another
A 2017 theory proposed by Rice University physicists to explain the contradictory behavior of an iron-based high-temperature superconductor is helping solve a puzzle in a different type of unconventional superconductor: the ‘heavy fermion’ compound known as CeCu2Si2.

An international team from the U.S., China, Germany and Canada recently reported their findings which focused on a cerium, copper and silicon composite whose strange behavior in 1979 helped usher in the multidisciplinary field of quantum materials, they said.

Stable levitation of a magnet atop an unconventional high-temperature superconductor.
Source: Rice University/LPS Orsay, France

That year, a team led by Max Planck Institute’s Frank Steglich, found that CeCu2Si2 became a superconductor at extremely cold temperatures. The mechanism of superconductivity couldn’t be explained by existing theory, and the finding was so unexpected and unusual that many physicists initially refused to accept it. The 1986 discovery of superconductivity at even higher temperatures in copper ceramics crystalized interest in the field and came to dominate the career of theoretical physicists like Rice’s Qimiao Si, a PNAS study co-author and the Harry C. and Olga K. Wiess Professor of Physics and Astronomy.

Si and Steglich have collaborated for decades, and their work has led to almost two dozen peer-reviewed studies. “In my wildest dreams, I had not thought that the theory that we proposed for the iron-based superconductors would come back to the other part of my life, which is the heavy-fermion superconductors,” Si said.

Like high-temperature superconductors, heavy fermions are what physicists call quantum materials because of the key role that quantum forces play in their behavior. In high-temperature superconductors, for example, electrons form pairs and flow without resistance at temperatures considerably warmer than those needed for conventional superconductivity. In heavy fermions, electrons appear to be thousands of times more massive than they should.

In 2001, Si offered a pioneering theory that these phenomena arise at critical transition points, tipping points where changes in pressure or other conditions bring about a transition from one quantum state to another. At the tipping point, or “quantum critical point,” electrons can develop a kind of split personality as they attempt to straddle the line between states.

Superconductivity illustrates how this can play out. In a normal copper wire, electrical resistance arises when flowing electrons jostle and bump against atoms in the wire. Each bump costs a small amount of energy, which is lost to heat. In superconductors, the electrons avoid this loss by pairing up and flowing in unison, without any bumps. And because electrons are among the most antisocial of subatomic particles, they repel one another and pair up only in extraordinary circumstances. In the case of conventional superconductors, tiny variations in the spacing between atoms in a supercooled wire can coax the electrons into a marriage of convenience. The mechanism in unconventional superconductors is different.

Si said the unifying understanding is that if two electrons work really hard to repel one other, there can still be an attractive force. “If I am moving because I don’t like being close to you, and you are doing the same, and yet we cannot be too far apart, it becomes a kind of dance. The pairs in high-temperature superconductors move in relation to one another, not unlike two dance partners that spin, even as they move together across the dance floor.”

Brainstem implant can preserve human hearing
Patients with rare brain tumors on the auditory nerve now have an option to prevent complete deafness at UC San Diego Health. The device, called an auditory brainstem implant (ABI), fits behind the ear and connects directly to the brainstem. The device enables patients with the inherited disorder neurofibromatosis type 2 (NF2) who develop bilateral hearing nerve tumors to be aware of environmental sounds, such as a door opening, a phone ringing or a car approaching.

An auditory brainstem implant has two parts: a sound processor, worn behind the ear, and an implant that connects below the skin.
Source: UC San Diego

Marc Schwartz, MD, neurosurgeon at UC San Diego Health said, “An auditory brainstem implant can have a profoundly positive impact on a patient’s quality of life. The device helps patients to perceive sound and communicate more effectively through lip reading. It was designed for patients with NF2 who may not benefit from traditional hearing devices. The highest performing patients with ABIs may develop the ability to understand some speech.”