Things aren’t always what they seem . . . or are they? Extreme close-ups often obscure the full picture. Cloaked in mystery, this new video series introduces a variety of objects and moments — found at MIT — that invite you to take a second look.
A team of engineers at MIT have developed a novel method to mass-produce tiny robots, no bigger than a cell, quickly, easily and accurately with little to no external stimulus.
The Massachusetts Institute of Technology is an independent, coeducational, privately endowed university in Cambridge, Massachusetts. Our mission is to advance knowledge; to educate students in science, engineering, and technology; and to tackle the most pressing problems facing the world today. We are a community of hands-on problem-solvers in love with fundamental science and eager to make the world a better place
MIT's Cheetah 3 robot can now leap and gallop across rough terrain, climb a staircase littered with debris, and quickly recover its balance when suddenly yanked or shoved, all while essentially blind.
The Massachusetts Institute of Technology is an independent, coeducational, privately endowed university in Cambridge, Massachusetts. Our mission is to advance knowledge; to educate students in science, engineering, and technology; and to tackle the most pressing problems facing the world today. We are a community of hands-on problem-solvers in love with fundamental science and eager to make the world a better place.
System allows drones to cooperatively explore terrain under thick forest canopies where GPS signals are unreliable.
Finding lost hikers in forests can be a difficult and lengthy process, as helicopters and drones can’t get a glimpse through the thick tree canopy. Recently, it’s been proposed that autonomous drones, which can bob and weave through trees, could aid these searches. But the GPS signals used to guide the aircraft can be unreliable or nonexistent in forest environments.
In a paper being presented at the International Symposium on Experimental Robotics conference next week, MIT researchers describe an autonomous system for a fleet of drones to collaboratively search under dense forest canopies. The drones use only onboard computation and wireless communication — no GPS required.
Each autonomous quadrotor drone is equipped with laser-range finders for position estimation, localization, and path planning. As the drone flies around, it creates an individual 3-D map of the terrain. Algorithms help it recognize unexplored and already-searched spots, so it knows when it’s fully mapped an area. An off-board ground station fuses individual maps from multiple drones into a global 3-D map that can be monitored by human rescuers.
In a real-world implementation, though not in the current system, the drones would come equipped with object detection to identify a missing hiker. When located, the drone would tag the hiker’s location on the global map. Humans could then use this information to plan a rescue mission.
“Essentially, we’re replacing humans with a fleet of drones to make the search part of the search-and-rescue process more efficient,” says first author Yulun Tian, a graduate student in the Department of Aeronautics and Astronautics (AeroAstro).
The researchers tested multiple drones in simulations of randomly generated forests, and tested two drones in a forested area within NASA’s Langley Research Center. In both experiments, each drone mapped a roughly 20-square-meter area in about two to five minutes and collaboratively fused their maps together in real-time. The drones also performed well across several metrics, including overall speed and time to complete the mission, detection of forest features, and accurate merging of maps.
Co-authors on the paper are: Katherine Liu, a PhD student in MIT’s Computer Science and Artificial Intelligence Laboratory (CSAIL) and AeroAstro; Kyel Ok, a PhD student in CSAIL and the Department of Electrical Engineering and Computer Science; Loc Tran and Danette Allen of the NASA Langley Research Center; Nicholas Roy, an AeroAstro professor and CSAIL researcher; and Jonathan P. How, the Richard Cockburn Maclaurin Professor of Aeronautics and Astronautics.
Exploring and mapping
On each drone, the researchers mounted a LIDAR system, which creates a 2-D scan of the surrounding obstacles by shooting laser beams and measuring the reflected pulses. This can be used to detect trees; however, to drones, individual trees appear remarkably similar. If a drone can’t recognize a given tree, it can’t determine if it’s already explored an area.
The researchers programmed their drones to instead identify multiple trees’ orientations, which is far more distinctive. With this method, when the LIDAR signal returns a cluster of trees, an algorithm calculates the angles and distances between trees to identify that cluster. “Drones can use that as a unique signature to tell if they’ve visited this area before or if it’s a new area,” Tian says.
This feature-detection technique helps the ground station accurately merge maps. The drones generally explore an area in loops, producing scans as they go. The ground station continuously monitors the scans. When two drones loop around to the same cluster of trees, the ground station merges the maps by calculating the relative transformation between the drones, and then fusing the individual maps to maintain consistent orientations.
“Calculating that relative transformation tells you how you should align the two maps so it corresponds to exactly how the forest looks,” Tian says.
In the ground station, robotic navigation software called “simultaneous localization and mapping” (SLAM) — which both maps an unknown area and keeps track of an agent inside the area — uses the LIDAR input to localize and capture the position of the drones. This helps it fuse the maps accurately.
The end result is a map with 3-D terrain features. Trees appear as blocks of colored shades of blue to green, depending on height. Unexplored areas are dark but turn gray as they’re mapped by a drone. On-board path-planning software tells a drone to always explore these dark unexplored areas as it flies around. Producing a 3-D map is more reliable than simply attaching a camera to a drone and monitoring the video feed, Tian says. Transmitting video to a central station, for instance, requires a lot of bandwidth that may not be available in forested areas.
More efficient searching
A key innovation is a novel search strategy that let the drones more efficiently explore an area. According to a more traditional approach, a drone would always search the closest possible unknown area. However, that could be in any number of directions from the drone’s current position. The drone usually flies a short distance, and then stops to select a new direction.
“That doesn’t respect dynamics of drone [movement],” Tian says. “It has to stop and turn, so that means it’s very inefficient in terms of time and energy, and you can’t really pick up speed.”
Instead, the researchers’ drones explore the closest possible area, while considering their current direction. They believe this can help the drones maintain a more consistent velocity. This strategy — where the drone tends to travel in a spiral pattern — covers a search area much faster. “In search and rescue missions, time is very important,” Tian says.
In the paper, the researchers compared their new search strategy with a traditional method. Compared to that baseline, the researchers’ strategy helped the drones cover significantly more area, several minutes faster and with higher average speeds.
One limitation for practical use is that the drones still must communicate with an off-board ground station for map merging. In their outdoor experiment, the researchers had to set up a wireless router that connected each drone and the ground station. In the future, they hope to design the drones to communicate wirelessly when approaching one another, fuse their maps, and then cut communication when they separate. The ground station, in that case, would only be used to monitor the updated global map.
Innovative approach to controlling magnetism could lead to next-generation memory and logic devices.
A new approach to controlling magnetism in a microchip could open the doors to memory, computing, and sensing devices that consume drastically less power than existing versions. The approach could also overcome some of the inherent physical limitations that have been slowing progress in this area until now.
Researchers at MIT and at Brookhaven National Laboratory have demonstrated that they can control the magnetic properties of a thin-film material simply by applying a small voltage. Changes in magnetic orientation made in this way remain in their new state without the need for any ongoing power, unlike today’s standard memory chips, the team has found.
The new finding is being reported today in the journal Nature Materials, in a paper by Geoffrey Beach, a professor of materials science and engineering and co-director of the MIT Materials Research Laboratory; graduate student Aik Jun Tan; and eight others at MIT and Brookhaven.
As silicon microchips draw closer to fundamental physical limits that could cap their ability to continue increasing their capabilities while decreasing their power consumption, researchers have been exploring a variety of new technologies that might get around these limits. One of the promising alternatives is an approach called spintronics, which makes use of a property of electrons called spin, instead of their electrical charge.
Because spintronic devices can retain their magnetic properties without the need for constant power, which silicon memory chips require, they need far less power to operate. They also generate far less heat — another major limiting factor for today’s devices.
But spintronic technology suffers from its own limitations. One of the biggest missing ingredients has been a way to easily and rapidly control the magnetic properties of a material electrically, by applying a voltage. Many research groups around the world have been pursuing that challenge.
Previous attempts have relied on electron accumulation at the interface between a metallic magnet and an insulator, using a device structure similar to a capacitor. The electrical charge can change the magnetic properties of the material, but only by a very small amount, making it impractical for use in real devices. There have also been attempts at using ions instead of electrons to change magnetic properties. For instance, oxygen ions have been used to oxidize a thin layer of magnetic material, causing a extremely large changes in magnetic properties. However, the insertion and removal of oxygen ions causes the material to swell and shrink, causing mechanical damage that limits the process to just a few repetitions — rendering it essentially useless for computational devices.
The new finding demonstrates a way around that, by using hydrogen ions instead of the much larger oxygen ions used in previous attempts. Since the hydrogen ions can zip in and out very easily, the new system is much faster and provides other significant advantages, the researchers say.
Because the hydrogen ions are so much smaller, they can enter and exit from the crystalline structure of the spintronic device, changing its magnetic orientation each time, without damaging the material. In fact, the team has now demonstrated that the process produces no degradation of the material after more than 2,000 cycles. And, unlike oxygen ions, hydrogen can easily pass through metal layers, which allows the team to control properties of layers deep in a device that couldn’t be controlled in any other way.
“When you pump hydrogen toward the magnet, the magnetization rotates,” Tan says. “You can actually toggle the direction of the magnetization by 90 degrees by applying a voltage — and it’s fully reversible.” Since the orientation of the poles of the magnet is what is used to store information, this means it is possible to easily write and erase data “bits” in spintronic devices using this effect.
Beach, whose lab discovered the original process for controlling magnetism through oxygen ions several years ago, says that initial finding unleashed widespread research on a new area dubbed “magnetic ionics,” and now this newest finding has “turned on its end this whole field.”
“This is really a significant breakthrough,” says Chris Leighton, the Distinguished McKnight University Professor in the Department of Chemical Engineering and Materials Science at the University of Minnesota, who was not involved in this work. “There is currently a great deal of interest worldwide in controlling magnetic materials simply by applying electrical voltages. It’s not only interesting from the fundamental side, but it’s also a potential game-changer for applications, where magnetic materials are used to store and process digital information.”
Leighton says, “Using hydrogen insertion to control magnetism is not new, but being able to do that in a voltage-driven way, in a solid-state device, with good impact on the magnetic properties — that is pretty significant!” He adds, “this is something new, with the potential to open up additional new areas of research. … At the end of the day, controlling any type of materials function by literally flipping a switch is pretty exciting. Being able to do that quickly enough, over enough cycles, in a general way, would be a fantastic advance for science and engineering.”
Essentially, Beach explains, he and his team are “trying to make a magnetic analog of a transistor,” which can be turned on and off repeatedly without degrading its physical properties.
Just add water
The discovery came about, in part, through serendipity. While experimenting with layered magnetic materials in search of ways of changing their magnetic behavior, Tan found that the results of his experiments varied greatly from day to day for reasons that were not apparent. Eventually, by examining all the conditions during the different tests, he realized that the key difference was the humidity in the air: The experiment worked better on humid days compared to dry ones. The reason, he eventually realized, was that water molecules from the air were being split up into oxygen and hydrogen on the charged surface of the material, and while the oxygen escaped to the air, the hydrogen became ionized and was penetrating into the magnetic device — and changing its magnetism.
The device the team has produced consists of a sandwich of several thin layers, including a layer of cobalt where the magnetic changes take place, sandwiched between layers of a metal such as palladium or platinum, and with an overlay of gadolinium oxide, and then a gold layer to connect to the driving electrical voltage.
The magnetism gets switched with just a brief application of voltage and then stays put. Reversing it requires no power at all, just short-circuiting the device to connect its two sides electrically, whereas a conventional memory chip requires constant power to maintain its state. “Since you’re just applying a pulse, the power consumption can go way down,” Beach says.
The new devices, with their low power consumption and high switching speed, could eventually be especially useful for devices such mobile computing, Beach says, but the work is still at an early stage and will require further development.
“I can see lab-based prototypes within a few years or less,” he says. Making a full working memory cell is “quite complex” and might take longer, he says.
The work was supported by the National Science Foundation through the Materials Research Science and Engineering Center (MRSEC) Program.
Neuroscientists discover a circuit that helps redirect attention to focus on potential threats.
Imagine a herd of deer grazing in the forest. Suddenly, a twig snaps nearby, and they look up from the grass. The thought of food is forgotten, and the animals are primed to respond to any threat that might appear.
MIT neuroscientists have now discovered a circuit that they believe controls the diversion of attention away from everyday pursuits, to focus on potential threats. They also found that dopamine is key to the process: It is released in the brain’s prefrontal cortex when danger is perceived, stimulating the prefrontal cortex to redirect its focus to a part of the brain that responds to threats.
“The prefrontal cortex has long been thought to be important for attention and higher cognitive functions — planning, prioritizing, decision-making. It’s as though dopamine is the signal that tells the router to switch over to sending information down the pathway for escape-related behavior,” says Kay Tye, an MIT associate professor of brain and cognitive sciences and a member of MIT’s Picower Institute for Learning and Memory.
When this circuit is off-balance, it could trigger anxious and paranoid behavior, possibly underlying some of the symptoms seen in schizophrenia, anxiety, and depression, Tye says.
Tye is the senior author of the study, which appears in the Nov. 7 issue of Nature. The lead authors are former graduate student Caitlin Vander Weele, postdoc Cody Siciliano, and research scientist Gillian Matthews.
One major role of the prefrontal cortex, which is the seat of conscious thought and other complex cognitive behavior, is to route information to different parts of the brain.
In this study, Tye identified two populations of neurons in the prefrontal cortex, based on other brain regions that they communicate with. One set of neurons sends information to the nucleus accumbens, which is involved in motivation and reward, and the other group relays information to the periaqueductal gray (PAG), which is part of the brainstem. The PAG is involved in defensive behavior such as freezing or running.
When we perceive a potentially dangerous event, a brain region called the ventral tegmental area (VTA) sends dopamine to the prefrontal cortex, and Tye and her colleagues wanted determine how dopamine affects the two populations they had identified. To achieve that, they designed an experiment where rats were trained to recognize two visual cues, one associated with sugar water and one with a mild electrical shock. Then, they explored what happened when both cues were presented at the same time.
They found that if they stimulated dopamine release at the same time that the cues were given, the rats were much more likely to freeze (their normal response to the shock cue) than to head for the port where they would receive the sugar water. If they stimulated dopamine when just one of the cues was given, the rats’ behavior was not affected, suggesting that dopamine’s role is to enhance the escape response when the animals receive conflicting information.
“The reward-associated neurons drop their spiking by a substantial amount, making it harder for you to pay attention to a reward,” Tye says.
Further experiments suggested that dopamine acts by adjusting the signal-to-noise ratio in neurons of the prefrontal cortex. “Noise” is random firing of neurons, while the “signal” is the meaningful input coming in, such as sensory information. When neurons that connect to the PAG receive dopamine at the same time as a threatening stimulus, their signal goes up and the noise decreases. The researchers aren’t sure how this happens, but they suspect that dopamine may activate other neurons that help to amplify the signals already coming into the PAG-connected neurons, and suppress the activity of neurons that project to the nucleus accumbens.
Adapted for survival
This brain circuit could help give animals a better chance of surviving a threatening situation, Tye says. Any kind of danger sign, such as the snapping twig that startles a herd of deer, or a stranger roughly bumping into you on the sidewalk, can produce a surge of dopamine in the prefrontal cortex. This dopamine then promotes enhanced vigilance.
“You would be on the defensive,” Tye says. “There may be some times that you run when you don’t need to, but more often than not, it might make sense to turn your attention to a potential threat.”
Dysregulation of this dopamine-controlled switching may contribute to neuropsychiatric disorders such as schizophrenia, Tye says. Among other effects, too much dopamine could lead the brain to weigh negative inputs too highly. This could result in paranoia, often seen in schizophrenia patients, or anxiety.
Tye now hopes to determine more precisely how dopamine affects other neurotransmitters involved in the modulation of the signal-to-noise ratio. She also plans to further explore the role of this kind of modulation in anxiety and phobias.
The research was funded by the JPB Foundation, the Picower Institute Innovation Fund, the Picower Neurological Disorders Research Fund, the Junior Faculty Development Program, the Klingenstein Foundation, a NARSAD Young Investigator Award, the New York Stem Cell Foundation, the National Institutes of Health, the NIH Director’s New Innovator Award, and the NIH Pioneer Award.