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Thursday, August 29th, 2019
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| 12:00a | MIT’s fleet of autonomous boats can now shapeshift MIT’s fleet of robotic boats has been updated with new capabilities to “shapeshift,” by autonomously disconnecting and reassembling into a variety of configurations, to form floating structures in Amsterdam’s many canals. The autonomous boats — rectangular hulls equipped with sensors, thrusters, microcontrollers, GPS modules, cameras, and other hardware — are being developed as part of the ongoing “Roboat” project between MIT and the Amsterdam Institute for Advanced Metropolitan Solutions (AMS Institute). The project is led by MIT professors Carlo Ratti, Daniela Rus, Dennis Frenchman, and Andrew Whittle. In the future, Amsterdam wants the roboats to cruise its 165 winding canals, transporting goods and people, collecting trash, or self-assembling into “pop-up” platforms — such as bridges and stages — to help relieve congestion on the city’s busy streets. In 2016, MIT researchers tested a roboat prototype that could move forward, backward, and laterally along a preprogrammed path in the canals. Last year, researchers designed low-cost, 3-D-printed, one-quarter scale versions of the boats, which were more efficient and agile, and came equipped with advanced trajectory-tracking algorithms. In June, they created an autonomous latching mechanism that let the boats target and clasp onto each other, and keep trying if they fail. In a new paper presented at the last week’s IEEE International Symposium on Multi-Robot and Multi-Agent Systems, the researchers describe an algorithm that enables the roboats to smoothly reshape themselves as efficiently as possible. The algorithm handles all the planning and tracking that enables groups of roboat units to unlatch from one another in one set configuration, travel a collision-free path, and reattach to their appropriate spot on the new set configuration.
“We’ve enabled the roboats to now make and break connections with other roboats, with hopes of moving activities on the streets of Amsterdam to the water,” says Rus, director of the Computer Science and Artificial Intelligence Laboratory (CSAIL) and the Andrew and Erna Viterbi Professor of Electrical Engineering and Computer Science. “A set of boats can come together to form linear shapes as pop-up bridges, if we need to send materials or people from one side of a canal to the other. Or, we can create pop-up wider platforms for flower or food markets.” Joining Rus on the paper are: Ratti, director of MIT’s Senseable City Lab, and, also from the lab, first author Banti Gheneti, Ryan Kelly, and Drew Meyers, all researchers; postdoc Shinkyu Park; and research fellow Pietro Leoni. Collision-free trajectories For their work, the researchers had to tackle challenges with autonomous planning, tracking, and connecting groups of roboat units. Giving each unit unique capabilities to, for instance, locate each other, agree on how to break apart and reform, and then move around freely, would require complex communication and control techniques that could make movement inefficient and slow. To enable smoother operations, the researchers developed two types of units: coordinators and workers. One or more workers connect to one coordinator to form a single entity, called a “connected-vessel platform” (CVP). All coordinator and worker units have four propellers, a wireless-enabled microcontroller, and several automated latching mechanisms and sensing systems that enable them to link together. Coordinators, however, also come equipped with GPS for navigation, and an inertial measurement unit (IMU), which computes localization, pose, and velocity. Workers only have actuators that help the CVP steer along a path. Each coordinator is aware of and can wirelessly communicate with all connected workers. Structures comprise multiple CVPs, and individual CVPs can latch onto one another to form a larger entity. During shapeshifting, all connected CVPs in a structure compare the geometric differences between its initial shape and new shape. Then, each CVP determines if it stays in the same spot and if it needs to move. Each moving CVP is then assigned a time to disassemble and a new position in the new shape. Each CVP uses a custom trajectory-planning technique to compute a way to reach its target position without interruption, while optimizing the route for speed. To do so, each CVP precomputes all collision-free regions around the moving CVP as it rotates and moves away from a stationary one. After precomputing those collision-free regions, the CVP then finds the shortest trajectory to its final destination, which still keeps it from hitting the stationary unit. Notably, optimization techniques are used to make the whole trajectory-planning process very efficient, with the precomputation taking little more than 100 milliseconds to find and refine safe paths. Using data from the GPS and IMU, the coordinator then estimates its pose and velocity at its center of mass, and wirelessly controls all the propellers of each unit and moves into the target location. In their experiments, the researchers tested three-unit CVPs, consisting of one coordinator and two workers, in several different shapeshifting scenarios. Each scenario involved one CVP unlatching from the initial shape and moving and relatching to a target spot around a second CVP. Three CVPs, for instance, rearranged themselves from a connected straight line — where they were latched together at their sides — into a straight line connected at front and back, as well as an “L.” In computer simulations, up to 12 roboat units rearranged themselves from, say, a rectangle into a square or from a solid square into a Z-like shape.
Scaling up Experiments were conducted on quarter-sized roboat units, which measure about 1 meter long and half a meter wide. But the researchers believe their trajectory-planning algorithm will scale well in controlling full-sized units, which will measure about 4 meters long and 2 meters wide. In about a year, the researchers plan to use the roboats to form into a dynamic “bridge” across a 60-meter canal between the NEMO Science Museum in Amsterdam’s city center and an area that’s under development. The project, called RoundAround, will employ roboats to sail in a continuous circle across the canal, picking up and dropping off passengers at docks and stopping or rerouting when they detect anything in the way. Currently, walking around that waterway takes about 10 minutes, but the bridge can cut that time to around two minutes. “This will be the world’s first bridge comprised of a fleet of autonomous boats,” Ratti says. “A regular bridge would be super expensive, because you have boats going through, so you’d need to have a mechanical bridge that opens up or a very high bridge. But we can connect two sides of canal [by using] autonomous boats that become dynamic, responsive architecture that float on the water.” To reach that goal, the researchers are further developing the roboats to ensure they can safely hold people, and are robust to all weather conditions, such as heavy rain. They’re also making sure the roboats can effectively connect to the sides of the canals, which can vary greatly in structure and design. |
| 12:00a | New science blooms after star researchers die, study finds The famed quantum physicist Max Planck had an idiosyncratic view about what spurred scientific progress: death. That is, Planck thought, new concepts generally take hold after older scientists with entrenched ideas vanish from the discipline. “A great scientific truth does not triumph by convincing its opponents and making them see the light, but rather because its opponents eventually die, and a new generation grows up that is familiar with it,” Planck once wrote. Now a new study co-authored by MIT economist Pierre Azoulay, an expert on the dynamics of scientific research, concludes that Planck was right. In many areas of the life sciences, at least, the deaths of prominent researchers are often followed by a surge in highly cited research by newcomers to those fields. Indeed, when star scientists die, their subfields see a subsequent 8.6 percent increase, on average, of articles by researchers who have not previously collaborated with those star scientists. Moreover, those papers published by the newcomers to these fields are much more likely to be influential and highly cited than other pieces of research. “The conclusion of this paper is not that stars are bad,” says Azoulay, who has co-authored a new paper detailing the study’s findings. “It’s just that, once safely ensconsed at the top of their fields, maybe they tend to overstay their welcome.” The paper, “Does Science Advance one Funeral at a Time?” is co-authored by Azoulay, the International Programs Professor of Management at the MIT Sloan School of Management; Christian Fons-Rosen, an assistant professor of economics at the University of California at Merced; and Joshua Graff Zivin, a professor of economics at the University of California at San Diego and faculty member in the university’s School of Global Policy and Strategy. It is forthcoming in the American Economic Review. To conduct the study, the researchers used a database of life scientists that Azoulay and Graff Zivin have been building for well over a decade. In it, the researchers chart the careers of life scientists, looking at accomplishments that include funding awards, published papers and the citations of those papers, and patent statistics. In this case, Azoulay, Graff Zivin, and Fons-Rosen studied what occurred after the unexpected deaths of 452 life scientists, who were still active in their disciplines. In addition to the 8.6 percent increase in papers by new entrants to those subfields, there was a 20.7 percent decrease in papers by the rather smaller number of scientists who had previously co-authored papers with the star scientists. Overall, Azoulay notes, the study provides a window into the power structures of scientific disciplines. Even if well-established scientists are not intentionally blocking the work of researchers with alternate ideas, a group of tightly connected colleagues may wield considerable influence over journals and grant awards. In those cases, “it’s going to be harder for those outsiders to make a mark on the domain,” Azoulay notes. “The fact that if you’re successful, you get to set the intellectual agenda of your field, that is part of the incentive system of science, and people do extraordinary positive things in the hope of getting to that position,” Azoulay notes. “It’s just that, once they get there, over time, maybe they tend to discount ‘foreign’ ideas too quickly and for too long.” Thus what the researchers call “Planck’s Principle” serves as an unexpected — and tragic — mechanism for diversifying bioscience research. The researchers note that in referencing Planck, they are extending his ideas to a slightly different setting than the one he himself was describing. In his writing, Planck was discussing the birth of quantum physics — the kind of epochal, paradigm-setting shift that rarely occurs in science. The current study, Azoulay notes, examines what happens in everyday “normal science,” in the phrase of philosopher Thomas Kuhn. The process of bringing new ideas into science, and then hanging on to them, is only to be expected in many areas of research, according to Azoulay. Today’s seemingly stodgy research veterans were once themselves innovators facing an old guard. “They had to hoist themselves atop the field in the first place, when presumably they were [fighting] the same thing,” Azoulay says. “It’s the circle of life.” Or, in this case, the circle of life science. The research received support from the National Science Foundation, the Spanish Ministry of Economy and Competitiveness, and the Severo Ochoa Programme for Centres of Excellence in R&D. |
| 11:59p | For first time, astronomers catch asteroid in the act of changing color Last December, scientists discovered an “active” asteroid within the asteroid belt, sandwiched between the orbits of Mars and Jupiter. The space rock, designated by astronomers as 6478 Gault, appeared to be leaving two trails of dust in its wake — active behavior that is associated with comets but rarely seen in asteroids. While astronomers are still puzzling over the cause of Gault’s comet-like activity, an MIT-led team now reports that it has caught the asteroid in the act of changing color, in the near-infrared spectrum, from red to blue. It is the first time scientists have observed a color-shifting asteroid, in real-time. “That was a very big surprise,” says Michael Marsset, a postdoc in MIT’s Department of Earth, Atmospheric and Planetary Sciences (EAPS). “We think we have witnessed the asteroid losing its reddish dust to space, and we are seeing the asteroid’s underlying, fresh blue layers.” Marsset and his colleagues have also confirmed that the asteroid is rocky — proof that the asteroid’s tail, though seemingly comet-like, is caused by an entirely different mechanism, as comets are not rocky but more like loose snowballs of ice and dust. “It’s the first time to my knowledge that we see a rocky body emitting dust, a little bit like a comet,” Marsset says. “It means that probably some mechanism responsible for dust emission is different from comets, and different from most other active main-belt asteroids.” Marsset and his colleagues, including EAPS Research Scientist Francesca DeMeo and Professor Richard Binzel, have published their results today in the journal Astrophysical Journal Letters. A rock with tails Astronomers first discovered 6478 Gault in 1988 and named the asteroid after planetary geologist Donald Gault. Until recently, the space rock was seen as relatively average, measuring about 2.5 miles wide and orbiting along with millions of other bits of rock and dust within the inner region of the asteroid belt, 214 million miles from the sun. In January, images from various observatories, including NASA’s Hubble Space Telescope, captured two narrow, comet-like tails trailing the asteroid. Astronomers estimate that the longer tail stretches half a million miles out, while the shorter tail is about a quarter as long. The tails, they concluded, must consist of tens of millions of kilograms of dust, actively ejected by the asteroid, into space. But how? The question reignited interest in Gault, and studies since then have unearthed past instances of similar activity by the asteroid. “We know of about a million bodies between Mars and Jupiter, and maybe about 20 that are active in the asteroid belt,” Marsset says. “So this is very rare.” He and his colleagues joined the search for answers to Gault’s activity in March, when they secured observation time at NASA’s Infrared Telescope Facility (IRTF) on Mauna Kea, Hawaii. Over two nights, they observed the asteroid and used a high-precision spectrograph to divide the asteroid’s incoming light into various frequencies, or colors, the relative intensities of which can give scientists an idea of an object’s composition. From their analysis, the team determined that the asteroid’s surface is composed mainly of silicate, a dry, rocky material, similar to most other asteroids, and, more importantly, not at all like most comets. Comets typically come from the far colder edges of the solar system. When they approach the sun, any surface ice instantly sublimates, or vaporizes into gas, creating the comet’s characteristic tail. Since Marsset’s team has found 6478 Gault is a dry, rocky body, this means it likely is generating dust tails by some other active mechanism. A fresh change As the team observed the asteroid, they discovered, to their surprise, that the rock was changing color in the near-infrared, from red to blue. “We've never seen such a dramatic change like this over such a short period of time,” says co-author DeMeo. The scientists say they are likely seeing the asteroid’s surface dust, turned red over millions of years of exposure to the sun, being ejected into space, revealing a fresh, less irradiated surface beneath, that appears blue at near-infrared wavelengths. “Interestingly, you only need a very thin layer to be removed to see a change in the spectrum,” DeMeo says. “It could be as thin as a single layer of grains just microns deep.” So what could be causing the asteroid to turn color? The team and other groups studying 6478 Gault believe the reason for the color shift, and the asteroid’s comet-like activity, is likely due to the same mechanism: a fast spin. The asteroid may be spinning fast enough to whip off layers of dust from its surface, through sheer centrifugal force. The researchers estimate it would need to have about a two-hour rotation period, spinning around every couple of hours, versus Earth’s 24-hour period. “About 10 percent of asteroids spin very fast, meaning with a two- to three-hour rotation period, and it’s most likely due to the sun spinning them up,” says Marsset. This spinning phenomenon is known as the YORP effect (or, the Yarkovsky-O’Keefe-Radzievskii-Paddack effect, named after the scientists who discovered it), which refers to the effect of solar radiation, or photons, on small, nearby bodies such as asteroids. While asteroids reflect most of this radiation back into space, a fraction of these photons is absorbed, then reemitted as heat, and also momentum. This creates a small force that, over millions of years, can cause the asteroid to spin faster. Astronomers have observed the YORP effect on a handful of asteroids in the past. To confirm a similar effect is acting on 6478 Gault, researchers will have to detect its spin through light curves — measurements of the asteroid’s brightness over time. The challenge will be to see through the asteroid’s considerable dust tail, which can obscure key portions of the asteroid’s light. Marsset’s team, along with other groups, plan to study the asteroid for further clues to activity, when it next becomes visible in the sky. “I think [the group’s study] reinforces the fact that the asteroid belt is a really dynamic place,” DeMeo says. “While the asteroid fields you see in the movies, all crashing into each other, is an exaggeration, there is definitely a lot happening out there every moment.” This research was funded, in part, by the NASA Planetary Astronomy Program. |
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