Friday, February 4, 2011
2/04/2011 03:07:00 AM Publicado por Alquimia
Want to build a really tough robot? Forget about Terminator. Instead, watch a tadpole turn into a frog.
Or at least that’s not too far off from what University of Vermont roboticist Josh Bongard has discovered, as he reports in the January 10 online edition of the Proceedings of the National Academy of Sciences.
In a first-of-its-kind experiment, Bongard created both simulated and actual robots that, like tadpoles becoming frogs, change their body forms while learning how to walk. And, over generations, his simulated robots also evolved, spending less time in “infant” tadpole-like forms and more time in “adult” four-legged forms.
These evolving populations of robots were able to learn to walk more rapidly than ones with fixed body forms. And, in their final form, the changing robots had developed a more robust gait -- better able to deal with, say, being knocked with a stick -- than the ones that had learned to walk using upright legs from the beginning.
“This paper shows that body change, morphological change, actually helps us design better robots,” Bongard says. “That’s never been attempted before.”
Bongard’s research, supported by the National Science Foundation, is part of a wider venture called evolutionary robotics. “We have an engineering goal,” he says “to produce robots as quickly and consistently as possible.” In this experimental case: upright four-legged robots that can move themselves to a light source without falling over.
“But we don’t know how to program robots very well,” Bongard says, because robots are complex systems. In some ways, they are too much like people for people to easily understand them.
“They have lots of moving parts. And their brains, like our brains, have lots of distributed materials: there’s neurons and there’s sensors and motors and they’re all turning on and off in parallel,” Bongard says, “and the emergent behavior from the complex system which is a robot, is some useful task like clearing up a construction site or laying pavement for a new road.” Or at least that’s the goal.
But, so far, engineers have been largely unsuccessful at creating robots that can continually perform simple, yet adaptable, behaviors in unstructured or outdoor environments.
Which is why Bongard, an assistant professor in UVM’s College of Engineering and Mathematical Sciences, and other robotics experts have turned to computer programs to design robots and develop their behaviors -- rather than trying to program the robots’ behavior directly.
His new work may help.
Using a sophisticated computer simulation, Bongard unleashed a series of synthetic beasts that move about in a 3-dimensional space. “It looks like a modern video game,” he says. Each creature -- or, rather, generations of the creatures -- then run a software routine, called a genetic algorithm, that experiments with various motions until it develops a slither, shuffle, or walking gait -- based on its body plan -- that can get it to the light source without tipping over.
“The robots have 12 moving parts,” Bongard says. “They look like the simplified skeleton of a mammal: it’s got a jointed spine and then you have four sticks -- the legs -- sticking out.”
Some of the creatures begin flat to the ground, like tadpoles or, perhaps, snakes with legs; others have splayed legs, a bit like a lizard; and others ran the full set of simulations with upright legs, like mammals.
And why do the generations of robots that progress from slithering to wide legs and, finally, to upright legs, ultimately perform better, getting to the desired behavior faster?
“The snake and reptilian robots are, in essence, training wheels,” says Bongard, “they allow evolution to find motion patterns quicker, because those kinds of robots can’t fall over. So evolution only has to solve the movement problem, but not the balance problem, initially. Then gradually over time it’s able to tackle the balance problem after already solving the movement problem.”
Sound anything like how a human infant first learns to roll, then crawl, then cruise along the coffee table and, finally, walk?
“Yes,” says Bongard, “We’re copying nature, we’re copying evolution, we’re copying neural science when we’re building artificial brains into these robots.” But the key point is that his robots don’t only evolve their artificial brain -- the neural network controller -- but rather do so in continuous interaction with a changing body plan. A tadpole can’t kick its legs, because it doesn’t have any yet; it’s learning some things legless and others with legs.
And this may help to explain the most surprising -- and useful -- finding in Bongard’s study: the changing robots were not only faster in getting to the final goal, but afterward were more able to deal with new kinds of challenges that they hadn’t before faced, like efforts to tip them over.
Bongard is not exactly sure why this is, but he thinks it’s because controllers that evolved in the robots whose bodies changed over generations learned to maintain the desired behavior over a wider range of sensor-motor arrangements than controllers evolved in robots with fixed body plans. It seem that learning to walk while flat, squat, and then upright, gave the evolving robots resilience to stay upright when faced with new disruptions. Perhaps what a tadpole learns before it has legs makes it better able to use its legs once they grow.
“Realizing adaptive behavior in machines has to date focused on dynamic controllers, but static morphologies,” Bongard writes in his PNAS paper “This is an inheritance from traditional artificial intelligence in which computer programs were developed that had no body with which to affect, and be affected by, the world.”
“One thing that has been left out all this time is the obvious fact that in nature it’s not that the animal’s body stays fixed and its brain gets better over time,” he says, “in natural evolution animals bodies and brains are evolving together all the time.” A human infant, even if she knew how, couldn’t walk: her bones and joints aren’t up to the task until she starts to experience stress on the foot and ankle.
That hasn’t been done in robotics for an obvious reason: “it’s very hard to change a robot’s body,” Bongard says, “it’s much easier to change the programming inside its head.”
Still, Bongard gave it a try. After running 5000 simulations, each taking 30 hours on the parallel processors in UVM’s Vermont Advanced Computing Center -- “it would have taken 50 or 100 years on a single machine,” Bongard says—he took the task into the real world.
“We built a relatively simple robot, out of a couple of Lego Mindstorm kits, to demonstrate that you actually could do it,” he says. This physical robot is four-legged, like in the simulation, but the Lego creature wears a brace on its front and back legs. “The brace gradually tilts the robot,” as the controller searches for successful movement patterns, Bongard says, “so that the legs go from horizontal to vertical, from reptile to quadruped.
“While the brace is bending the legs, the controller is causing the robot to move around, so it’s able to move its legs, and bend its spine,” he says, “it’s squirming around like a reptile flat on the ground and then it gradually stands up until, at the end of this movement pattern, it’s walking like a coyote.”
“It’s a very simple prototype,” he says, “but it works; it’s a proof of concept.”
(Photo: University of Vermont)
University of Vermont
2/04/2011 03:06:00 AM Publicado por Alquimia
The eyes of moths, which allow them to see well at night, are also covered with a water-repellent, antireflective coating that makes their eyes among the least reflective surfaces in nature and helps them hide from predators in the dark. Mimicking the moth eye's microstructure, a team of researchers in Japan has created a new film, suitable for mass-production, for covering solar cells that can cut down on the amount of reflected light and help capture more power from the sun.
In a paper appearing in Energy Express (www.OpticsInfoBase.org/ee), a bi-monthly supplement to Optics Express, the open-access journal published by the Optical Society (OSA), the team describes how this film improves the performance of photovoltaic modules in laboratory and field experiments, and they calculate how the anti-reflection film would improve the yearly performance of solar cells deployed over large areas in either Tokyo, Japan or Phoenix, Ariz.
"Surface reflections are an essential loss for any type of photovoltaic module, and ultimately low reflections are desired," says Noboru Yamada, a scientist at Nagaoka University of Technology Japan, who led the research with colleagues at Mitsubishi Rayon Co. Ltd. and Tokyo Metropolitan University.
The team chose to look at the effect of deploying this antireflective moth-eye film on solar cells in Phoenix and Tokyo because Phoenix is a "sunbelt" city, with high annual amount of direct sunlight, while Tokyo is well outside the sunbelt region with a high fraction of diffuse solar radiation.
They estimate that the films would improve the annual efficiency of solar cells by 6 percent in Phoenix and by 5 percent in Tokyo.
"People may think this improvement is very small, but the efficiency of photovoltaics is just like fuel consumption rates of road vehicles," says Yamada. "Every little bit helps."
Yamada and his colleagues found the inspiration for this new technology a few years ago after they began looking for a broad-wavelength and omnidirectional antireflective structure in nature. The eyes of the moth were the best they found.
The difficulty in making the film, says Yamada, was designing a seamless, high-throughput roll-to-roll process for nanoimprinting the film. This was ultimately solved by Hideki Masuda, one of the authors on the Energy Express paper, and his colleagues at Mitsubishi Rayon Co. Ltd.
The team is now working on improving the durability of the film and optimizing it for many different types of solar cells. They also believe the film could be applied as an anti-reflection coating to windows and computer displays.
2/04/2011 03:04:00 AM Publicado por Alquimia
The discovery of an ancient fossil, nicknamed 'Mrs T', has allowed scientists for the first time to sex pterodactyls – flying reptiles that lived alongside dinosaurs between 220-65 million years ago.
Pterodactyls featured prominently in Spielberg's Jurassic Park III and are a classic feature of many dinosaur movies where they are often depicted as giant flying reptiles with a crest.
The discovery of a flying reptile fossilised together with an egg in Jurassic rocks (about 160 million years old) in China provides the first direct evidence for gender in these extinct fliers. This fossil shows that females were crestless, solving the long-standing problem of what some pterosaurs did with their spectacular head crests: showy displays by males.
The find was made by an international team of researchers from the Universities of Leicester, Lincoln and the Geological Institute, Beijing. Details of the unique new find are published (January 21) in the journal Science.
David Unwin, a palaeobiologist in the Department of Museum Studies at the University of Leicester, was part of the research team that studied the fossil. He said:
"Pterosaurs, flying reptiles, also known as pterodactyls, dominated the skies in the Mesozoic Era, the age of dinosaurs, 220-65 million years ago. Many pterosaurs have head crests. In the most spectacular cases these can reach five times the height of the skull. Scientists have long suspected that these crests were used for some kind of display or signalling and may have been confined to males, while females were crestless. But, in the absence of any direct evidence for gender this idea remained speculative and crested and crestless forms were often separated into completely different species."
"The fossil we have discovered, an individual of Darwinopterus (a pterosaur first described by the same team of scientists in 2009) is preserved together with an egg showing that it must be female. This type of discovery, in which gender can be determined with certainty, is extremely rare in the fossil record, and the first to be reported for pterosaurs."
The new discovery, christened "Mrs T" (a contraction of "Mrs Pterodactyl") by the research team, was made in Jurassic rocks of Liaoning Province in northeast China and seems to represent a tragic accident. The well developed shell shows that Mrs T was just about ready to lay her egg when she was killed in an accident that broke her left forearm, possibly the result of a storm, or perhaps even a volcanic eruption, which were common in this part of China around 160 million years old.
Dr Unwin said: "Mrs T shows two features that distinguish her from male individuals of Darwinopterus. She has relatively large hips, to accommodate the passage of eggs, but no head crest. Males, on the other hand, have relatively small hips and a well developed head crest. Presumably they used this crest to intimidate rivals, or to attract mates such as Mrs T.
"Mrs T is a once in ten lifetime's discovery. As long as the skull or hips are preserved we can now confidently identify males and females of Darwinopterus and, even more importantly, we can use this technique to sex other pterosaurs because they often show differences in head crests and hips just as in Darwinopterus".
Dr Unwin added: "Gender is one of the most fundamental of biological attributes, but extremely difficult to pinpoint with any certainty in the fossil record. Being able to sex pterosaurs is a major step forward. Finally, we have a good explanation for pterosaur head crests, a problem that has puzzled scientists for more than 100 years. Now, we can exploit our knowledge of pterosaur gender to research entirely new areas such as population structure and behaviour. We can also play matchmaker for pterosaurs bringing back together long separated males and females in the single species to which they both belong".
Apart from gender the new find also has much to tell us about pterosaur reproduction. Said Dr Unwin: "Mrs T's egg is relatively small and had a soft shell. This is typical of reptiles, but completely different from birds which lay relatively large hard-shelled eggs. This discovery is not surprising though, because a small egg would require less investment in terms of materials and energy – a distinct evolutionary advantage for active energetic fliers such as pterosaurs and perhaps an important factor in the evolution of gigantic species such as the 10 meter wingspan Quetzalcoatlus."
(Photo: Mark Witton)
University of Leicester