Wednesday, February 19, 2014

Robotic Construction Crew Needs No Foreman

The TERMES robots can carry bricks, build staircases, and climb them to add bricks to a structure, following low-level rules to independently complete a construction project.
Credit: Eliza Grinnell, Harvard SEAS
On the plains of Namibia, millions of tiny termites are building a mound of soil -- an 8-foot-tall "lung" for their underground nest. During a year of construction, many termites will live and die, wind and rain will erode the structure, and yet the colony's life-sustaining project will continue.

Inspired by the termites' resilience and collective intelligence, a team of computer scientists and engineers at the Harvard School of Engineering and Applied Sciences (SEAS) and the Wyss Institute for Biologically Inspired Engineering at Harvard University has created an autonomous robotic construction crew. The system needs no supervisor, no eye in the sky, and no communication: just simple robots -- any number of robots -- that cooperate by modifying their environment.

Harvard's TERMES system demonstrates that collective systems of robots can build complex, three-dimensional structures without the need for any central command or prescribed roles. The results of the four-year project were presented this week at the AAAS 2014 Annual Meeting and published in the February 14 issue of Science.

The TERMES robots can build towers, castles, and pyramids out of foam bricks, autonomously building themselves staircases to reach the higher levels and adding bricks wherever they are needed. In the future, similar robots could lay sandbags in advance of a flood, or perform simple construction tasks on Mars.

"The key inspiration we took from termites is the idea that you can do something really complicated as a group, without a supervisor, and secondly that you can do it without everybody discussing explicitly what's going on, but just by modifying the environment," says principal investigator Radhika Nagpal, Fred Kavli Professor of Computer Science at Harvard SEAS. She is also a core faculty member at the Wyss Institute, where she co-leads the Bioinspired Robotics platform.

Most human construction projects today are performed by trained workers in a hierarchical organization, explains lead author Justin Werfel, a staff scientist in bioinspired robotics at the Wyss Institute and a former SEAS postdoctoral fellow.

"Normally, at the beginning, you have a blueprint and a detailed plan of how to execute it, and the foreman goes out and directs his crew, supervising them as they do it," he says. "In insect colonies, it's not as if the queen is giving them all individual instructions. Each termite doesn't know what the others are doing or what the current overall state of the mound is."

Instead, termites rely on a concept known as stigmergy, a kind of implicit communication: they observe each others' changes to the environment and act accordingly. That is what Nagpal's team has designed the robots to do, with impressive results. Supplementary videos published with the Science paper show the robots cooperating to build several kinds of structures and even recovering from unexpected changes to the structures during construction.

Each robot executes its building process in parallel with others, but without knowing who else is working at the same time. If one robot breaks, or has to leave, it does not affect the others. This also means that the same instructions can be executed by five robots or five hundred. The TERMES system is an important proof of concept for scalable, distributed artificial intelligence.

Nagpal's Self-Organizing Systems Research Group specializes in distributed algorithms that allow very large groups of robots to act as a colony. Close connections between Harvard's computer scientists, electrical engineers, and biologists are key to her team's success. They created a swarm of friendly Kilobots a few years ago and are contributing artificial intelligence expertise to the ongoing RoboBees project, in collaboration with Harvard faculty members Robert J. Wood and Gu-Yeon Wei.

"When many agents get together -- whether they're termites, bees, or robots -- often some interesting, higher-level behavior emerges that you wouldn't predict from looking at the components by themselves," says Werfel. "Broadly speaking, we're interested in connecting what happens at the low level, with individual agent rules, to these emergent outcomes."

Coauthor Kirstin Petersen, a graduate student at Harvard SEAS with a fellowship from the Wyss Institute, spearheaded the design and construction of the TERMES robots and bricks. These robots can perform all the necessary tasks -- carrying blocks, climbing the structure, attaching the blocks, and so on -- with only four simple types of sensors and three actuators.

"We co-designed robots and bricks in an effort to make the system as minimalist and reliable as possible," Petersen says. "Not only does this help to make the system more robust; it also greatly simplifies the amount of computing required of the onboard processor. The idea is not just to reduce the number of small-scale errors, but more so to detect and correct them before they propagate into errors that can be fatal to the entire system."

In contrast to the TERMES system, it is currently more common for robotic systems to depend on a central controller. These systems typically rely on an "eye in the sky" that can see the whole process or on all of the robots being able to talk to each other frequently. These approaches can improve group efficiency and help the system recover from problems quickly, but as the numbers of robots and the size of their territory increase, these systems become harder to operate. In dangerous or remote environments, a central controller presents a single failure point that could bring down the whole system.

"It may be that in the end you want something in between the centralized and the decentralized system -- but we've proven the extreme end of the scale: that it could be just like the termites," says Nagpal. "And from the termites' point of view, it's working out great."

This research was supported by the Wyss Institute for Biologically Inspired Engineering at Harvard University.

What can a TERMES robot do?

- Move forward, backward, and turn in place
- Climb up or down a step the height of one brick
- Pick up a brick, carry it, and deposit it directly in front of itself
- Detect other bricks and robots in immediate vicinity
- Keep track of its own location with respect to a "seed" brick

What instructions do the TERMES robots follow?

- Obey predetermined traffic rules
- Circle the growing structure to find the first, "seed" brick (for orientation)
- Climb onto the structure
- Obtain a brick
- Attach the brick at any vacant point that satisfies local geometric requirements
- Climb off the structure
- Repeat

Sunday, February 16, 2014

JBC NOAA Green Roof Profiled

The NOAA Southwest Fisheries Green Roof in La Jolla, California designed by Jeffrey L. Bruce & Company is profiled on "A Growing Passion" hosted by Nan Sterman

Study Proves Organic Farming Boosts Biodiversity

Organic farms have around a third more species than conventionally-farmed ones, according to new research.

English countryside

There's been lots of investigation of how different agricultural methods affect the diversity of life present on farms, but the results vary between studies and from place to place. So a group of scientists analysed 94 earlier studies, concluding that organic farming methods increased the number of species on average by 34 per cent - an effect that's been stable over three decades and shows no sign of diminishing.

But this is only true of farms in temperate climates. Until more research is done we won't know if we're increasing biodiversity at all by paying more for organic versions of products like bananas and chocolate that grow in warmer climates. 'Our study shows that organic farming can yield significant long-term benefits for biodiversity,' says Sean Tuck, a PhD student at the University of Oxford and lead author of the paper, which appears in Journal of Applied Ecology. 'Organic methods could go some way towards halting the continued loss of diversity in industrialised nations.'

Some organisms benefit more than others. Plants underwent the greatest increase, with the number of species present increasing by around 70 per cent. Pollinators came second, with half as many species again on organic farms, while birds, arthropods and microbes also did well. Organisms that decompose dead matter showed little effect, although this may be partly because they are comparatively little-studied.

The benefit to biodiversity seems to be greater in intensively-farmed regions, particularly on organic farms surrounded by arable land. So it could be that having a few organic farms scattered around the landscape could benefit the intensively-cultivated farms in between by providing islands of biodiversity to nurture valuable organisms like bees, which pollinate crops, and predators, which help keep pests under control.

But Tuck argues the situation is more complex. It's true that many of the organisms that find refuge on organic farms can benefit surrounding intensively-cultivated ones. But on the other hand, intensive farming methods may damage the biodiversity nurtured on the organic farm. For instance, if neighbouring farms receive large doses of pesticide, bees and other pollinators from the organic farm may be badly harmed as well. 'The effect goes both ways,' he says. 'It depends on the scale you are looking at - a single isolated organic farm is likely to see more species, but at the landscape level the overall impact is much less clear.'

The study's results apply only to species richness, or the number of species present; they don't tell us anything about how many individuals of each species there were. There aren't as many studies of this abundance as of species richness, so Tuck says including it in the analysis would have reduced the amount of evidence that could be used and weakened the study's conclusions.

The concept of intensive farming is itself more complex than it might seem. 'Some conventional farms will intensively spray pesticides and fertilisers whereas others will use mixed methods of crop rotation and organic fertilisers with minimal chemical pesticides,' says Dr Lindsay Turnbull, also of Oxford, the paper's senior author.

She adds that existing research has been biased towards temperate UK and European climates, and that more studies of the impact of organic farming in tropical, subtropical and Mediterranean climates are needed.

'There are also regional differences in farming practices, and the majority of the studies in our data were in developed nations with long histories of farming such as those in Western Europe,' she explains. 'There, some wildlife have thrived in extensively managed farmland but are threatened by agricultural intensification. However, in developing nations there is often great pressure on the land to provide enough food for local people, resulting in the conversion of natural habitat to farmland. In such cases the benefits of organic farming are less clear, as this may require more land to achieve the same yield as conventional farming.'

Organic products like bananas and chocolate that are grown in hot climates are often marketed as being better for the environment, but without more research we don't know if this is true. 'At present, we simply cannot say whether buying organic bananas or chocolate has a clear environmental benefit,' Turnbull says.

Land-use intensity and the effects of organic farming on biodiversity: a hierarchical meta-analysis. Sean L. Tuck, Camilla Winqvist, Flávia Mota, Johan Ahnström, Lindsay A. Turnbull, Janne Bengtsson, DOI: 10.1111/1365-2664.12219