Caltech researchers Lulu Qian and Erik Winfree have managed to coax 130 strands of DNA into performing what is unquestionably a calculation: taking the square root of a number. (Ars Technica post; Science paper behind paywall; open-access background paper.) Not a big number: we’re talking about four-digit binary numbers, so 15 at the biggest. And not very efficiently: with prodding, the calculation took eight hours. Moore’s Law isn’t really in danger here.
“We found that ants almost always made networks that minimised the total amount of trail, consistent with optimisation at a colony level, rather than at an individual level,” Latty told iTnews. “In many cases, they did a remarkable job of making networks that looked almost exactly like the mathematical shortest path, called a ‘Steiner tree’.”
The Steiner tree problem is superficially similar to the minimum spanning tree problem: given a set V of points (vertices), interconnect them by a network (graph) of shortest length, where the length is the sum of the lengths of all edges. The difference between the Steiner tree problem and the minimum spanning tree problem is that, in the Steiner tree problem, extra intermediate vertices and edges may be added to the graph in order to reduce the length of the spanning tree.
The incredible woodland construction is a staggering 2,790 feet in length — more than half a mile long.
It is thought that several beaver families joined forces to create the massive dam, containing thousands of trees, and took many months to complete it.
Je ne suis pas certain de comprendre ce que montre l’image.