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7 4 STRESS RELIEF

TEAM BUILDING WITH HUMANS AND ROBOTS Constructionworkers on some sites are getting new, non-union help. SAM—short for semi-automated mason—is a robotic bricklayer being used to increase productivity as it works with humans. In this scenario, the robot is responsible for tasks such as picking up bricks, applying mor- tar, and brick placement while humans handle more nuanced activities, like setting up the worksite, laying bricks in tricky areas such as corners, and handling aesthetic details, like cleaning up excess mortar. SAM can complete precise and level work while being mounted on a scaffold that sways slightly in the wind. The robot can correct for differences between theoretical building specifications and what is actually on site, says Scott Peters, cofounder of Construction Robotics, Victor, N.Y., which designed SAM as its debut product. Peters says SAM’s purpose is to leverage human jobs, not entirely replace them. A human mason can lay 300 to 500 bricks a day, while SAM can lay 800 to 1200. One human plus one SAM equals the productivity of having four or more masons on the job. construction-robotics.com. SAM repetitively lays bricks while human masons handle the finishing touches.

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CONCRETE 3D PRINTING GETS SUPERSIZED Eindhoven University of Technology, the Netherlands, is using a concrete printer that enables objects up to 11 × 5 × 4 m to be printed. The printer looks a bit like an overhead hoisting crane in a production hall, but instead of a hoisting cable it features a swivel printer head for concrete. Attached to this via a hose is a concrete mixing and pump unit. The Dutch company ROHACO built the printer, the first of its kind. A complete wall can be printed with every required functionality— fiber-reinforced concrete to make it strong, an active insulation layer to retain heat, dirt-repelling exterior concrete to keep it clean, and a layer on the inside to enhance acoustics. www.tue.nl/en.

Top view of concrete printer. Courtesy of Eindhoven University of Technology/Rien Meulman.

KETCHUP OFFERS INSIGHTS INTO SOFT MATTER Soft matter consists of a huge class of materials that can behave either as liquids or sol- ids depending on circumstances. Soft matter can be found in everything from laptop screens and advanced batteries to ketchup, mayonnaise, and toothpaste. Cambridge University, UK, researchers developed new mathematical models to describe why these materials behave the way they do, which could help improve them for both domestic and high-tech applications. Professor Michael Cates discovered that mathematical models can explain how soft mate- rials can suddenly convert from liquid-like to solid-like behavior—through a process resembling an internal traffic jam. Cates discussed the jamming behavior of colloids and dense suspen- sions. Both are types of soft matter with an internal structure something like tiny ping-pong balls dispersed in a liquid. Researchers recently created active colloids in which the ping-pong balls are self-propelled, like tiny rockets. When their propulsion is switched on, these particles form tight clusters, despite having no attractive forces between them.

Heinz ketchup. Courtesy of Jeremy Brooks/Flickr.

“The question in this case is what causes the clustering?” wonders Cates. He concluded that each cluster is effectively a sort of traffic jam. When a dense suspension flows in response to stress, particles must push past each other. As long as the stress is low, they easily slide past with little friction between them. But when stress is increased, friction between particles also increases. www.cam.ac.uk.